Das Zettabyte Era Trends und Analysen Cisco Enhanced PDF Dieses Dokument ist Teil des Cisco Reg Visual Networking Index (VNI), einer laufenden Initiative zur Verfolgung und Prognose der Auswirkungen von visuellen Netzwerkanwendungen. Das Dokument stellt einige der wichtigsten Ergebnisse der globalen IP-Verkehrsprognose von Ciscos dar und untersucht die Auswirkungen des IP-Verkehrswachstums für Dienstanbieter. Für einen genaueren Blick auf die Prognose und die Methodik dahinter, besuchen Sie Cisco VNI: Forecast and Methodology, 20152020. Der jährliche globale IP-Verkehr wird bis Ende 2016 die Zettabyte (ZB 1000 Exabytes EB) überschreiten und bis 2020 2,3 ZB pro Jahr erreichen. Bis Ende 2016 erreicht der globale IP-Verkehr 1,1 ZB pro Jahr oder 88,7 EB pro Monat, und bis 2020 wird der weltweite IP-Verkehr 2,3 ZB pro Jahr erreichen bzw. 194 EB pro Monat. Der globale IP-Verkehr wird sich in den nächsten fünf Jahren fast verdoppeln. Insgesamt wird der IP-Verkehr mit einer jährlichen jährlichen Wachstumsrate (CAGR) von 22 Prozent von 2015 bis 2020 wachsen. Der monatliche IP-Verkehr wird bis 2020 auf 25 GB pro Kopf und bis 2015 auf 10 GB pro Kopf steigen Wächst schneller als der durchschnittliche Internetverkehr. Busy-Stunde (oder die verkehrsreichsten 60minute an einem Tag) Internet-Verkehr stieg um 51 Prozent im Jahr 2015, verglichen mit 29-Prozent-Wachstum im durchschnittlichen Verkehr. Busy-Stunden-Internet-Verkehr wird um den Faktor 4,6 zwischen 2015 und 2020 zu erhöhen, und durchschnittliche Internet-Verkehr wird um den Faktor 2 zu erhöhen. Der Smartphone-Verkehr wird bis zum Jahr 2020 den PC-Verkehr überschreiten. Im Jahr 2015 machten PCs 53 Prozent des gesamten IP-Verkehrs aus, aber bis 2020 werden PCs nur noch 29 Prozent des Verkehrs ausmachen. Smartphones werden 30 Prozent des gesamten IP-Traffic im Jahr 2020 ausmachen, von 8 Prozent im Jahr 2015. PC-gestarteten Verkehr wird bei einem CAGR von 8 Prozent und TVs, Tabletten, Smartphones und Machine-to-Machine (M2M) Module wachsen Werden Verkehrswachstumsraten von 17 Prozent, 39 Prozent, 58 Prozent und 44 Prozent haben. Der Verkehr von drahtlosen und mobilen Geräten wird bis zum Jahr 2020 zwei Drittel des gesamten IP-Verkehrs ausmachen. Bis 2020 werden kabelgebundene Geräte 34 Prozent des IP-Traffic ausmachen, und Wi-Fi und mobile Geräte werden für 66 Prozent des IP-Traffic verantwortlich sein. Im Jahr 2015, verkabelt Geräte für die Mehrheit der IP-Verkehr, mit 52 Prozent. Content Delivery Networks (CDNs) tragen bis zum Jahr 2020 fast zwei Drittel des Internet-Verkehrs. Vierundsechzig Prozent des gesamten Internetverkehrs werden die CDNs bis 2020 weltweit steigern, von 45 Prozent im Jahr 2015. Die Zahl der Geräte, die an IP-Netze angeschlossen sind, wird mehr als das Dreifache der Weltbevölkerung bis 2020 betragen. Es werden bis 2020 3,4 vernetzte Geräte pro Kopf und bis 2015 von 2,2 vernetzten Geräten pro Kopf kommen. Im Jahr 2020 werden es 26,3 Milliarden Netzwerkgeräte sein, von 16,3 Milliarden im Jahr 2015. Breitbandgeschwindigkeiten werden sich bis 2020 nahezu verdoppeln. Bis 2020 werden globale feste Breitband-Geschwindigkeiten erreichen 47,7 Mbps, von 24,7 Mbps im Jahr 2015. Globale Internet-Video-und Gaming-Highlights Es würde mehr als 5 Millionen Jahre dauern, um die Menge an Video, das globale IP-Netzwerke jeden Monat im Jahr 2020 zu überwachen. Jeder zweite, eine Million Minuten Videoinhalt wird das Netzwerk bis 2020 zu überqueren. Weltweit wird IP-Video-Verkehr 82 Prozent aller IP-Verkehr (sowohl für Unternehmen und Verbraucher) bis 2020 sein, von 70 Prozent im Jahr 2015. Global-IP-Video-Verkehr wird dreimal von 2015 bis 2020 wachsen, ein CAGR von 26 Prozent. Internet-Video-Verkehr wird vierfach von 2015 bis 2020 wachsen, ein CAGR von 31 Prozent. Internet Videoüberwachung Verkehr fast verdoppelt im Jahr 2015. Von 272 Petabyte pro Monat am Ende 2014 bis 516 Petabyte pro Monat im Jahr 2015. Internet Videoüberwachung Verkehr wird sich verzehnfacht zwischen 2015 und 2020. Weltweit werden 3,9 Prozent aller Internet-Video-Verkehr durch Videoüberwachung im Jahr 2020, von bis zu werden 1,5 Prozent im Jahr 2015. Virtual Reality Verkehr vervierfacht im Jahr 2015. Von 4,2 Petabyte (PB) pro Monat im Jahr 2014 auf 17,9 PB pro Monat im Jahr 2015. Weltweit wird die virtuelle Realität Verkehr 61-fach zwischen 2015 und 2020, ein CAGR von 127 Prozent zu erhöhen. Internet Video zu TV wuchs um 50 Prozent im Jahr 2015. Dieser Verkehr wird in einem rasanten Tempo wachsen und sich bis zum Jahr 2020 um das 3,6fache steigern. Internet Video to TV wird im Jahr 2020 26 Prozent des Internet-Videoverkehrs im Internet sein. Der VoIP-Verkehr wird sich bis 2020 nahezu verdoppeln . Die Menge des VoD-Verkehrs im Jahr 2020 entspricht 7,2 Milliarden DVDs pro Monat. Internet-Gaming-Verkehr wird siebenfach von 2015 bis 2020 wachsen. Ein CAGR von 46 Prozent. Weltweit wird der Internet-Gaming-Verkehr im Jahr 2020 4 Prozent des Internet-Verbrauchs im Internet sein - von 2 Prozent im Jahr 2015. Global Mobile Highlights Weltweit wird der mobile Datenverkehr zwischen 2015 und 2020 um das Achtfache zunehmen. Der mobile Datenverkehr wird zwischen 2015 und 2020 bei einem CAGR von 53 Prozent wachsen und bis 2020 30,6 Exabyte pro Monat erreichen. Der globale mobile Datenverkehr wird von 2015 bis 2020 fast dreimal so schnell wachsen wie der feste IP-Verkehr. Der feste IP-Verkehr wird zwischen 2015 und 2020 bei einem CAGR von 19 Prozent wachsen, während der mobile Datenverkehr bei einem CAGR von 53 Prozent wächst. Der globale mobile Datenverkehr belief sich im Jahr 2015 auf 5 Prozent des gesamten IP-Verkehrs und wird bis 2020 16 Prozent des gesamten IP-Verkehrs ausmachen. Der IP-Verkehr wächst am schnellsten im Nahen Osten und Afrika, gefolgt von Asien-Pazifik. Der Verkehr im Nahen Osten und Afrika wird zwischen 2015 und 2020 bei einem CAGR von 41 Prozent wachsen. Zusammenfassung der regionalen Wachstumsraten: Der IP-Verkehr in Nordamerika wird bis 2020 59,1 EB pro Monat erreichen und bei einem CAGR von 19 Prozent wachsen. IP-Verkehr in Westeuropa wird bis 2020 28,0 EB pro Monat erreichen und wächst mit einem CAGR von 20 Prozent. IP-Verkehr im asiatisch-pazifischen Raum erreicht 67,8 EB pro Monat bis zum Jahr 2020 und wächst mit einem CAGR von 22 Prozent. IP-Verkehr in Lateinamerika erreichen 11,6 EB pro Monat bis 2020 und wächst mit einem CAGR von 21 Prozent. IP-Verkehr in Mittel - und Osteuropa wird bis 2020 17,0 EB pro Monat erreichen und wächst mit einem CAGR von 27 Prozent. IP-Verkehr im Nahen Osten und Afrika wird 10,9 EB pro Monat bis 2020 erreichen, wächst mit einem CAGR von 41 Prozent. Hinweis: Mehrere interaktive Tools stehen zur Verfügung, um benutzerdefinierte Highlights und Prognose-Diagramme nach Regionen, Ländern, Applikationen und Endnutzersegmenten zu erstellen (siehe Cisco VNI Forecast Highlights und das Cisco VNI Forecast Widget-Tool). Global Business Highlights Business IP-Verkehr wird von einem CAGR von 18 Prozent von 2015 bis 2020 wachsen. Die zunehmende Akzeptanz von fortschrittlichen Videokommunikationen im Unternehmenssegment wird dazu führen, dass der Unternehmens-IP-Verkehr zwischen 2015 und 2020 um den Faktor 2 wächst. Der Geschäftsverkehr im Internet wird schneller wachsen als das IP-WAN. IP-WAN-Verkehr wächst bei einem CAGR von 6 Prozent, verglichen mit einem CAGR von 21 Prozent für feste Business-Internet und 47 Prozent für mobile Business Internet-Verkehr. Business-IP-Verkehr wird am schnellsten im Nahen Osten und Afrika. Business IP-Verkehr im Nahen Osten und Afrika wird bei einem CAGR von 21 Prozent wachsen, ein schnelleres Tempo als der globale Durchschnitt von 18 Prozent. In Volumen, Asien-Pazifik wird die größte Menge an Business-IP-Verkehr im Jahr 2019, bei 11,4 EB pro Monat. Nordamerika wird an zweiter Stelle sein, bei 9,1 EB pro Monat. Die aktuelle Prognose von Cisco Visual Networking Index (VNI) prognostiziert, dass der globale IP-Verkehr von 2015 bis 2020 nahezu verdreifachen wird. Anhang A enthält eine detaillierte Zusammenfassung. Der gesamte IP-Verkehr wird voraussichtlich bis 2020 auf 194 EB pro Monat ansteigen, von 72,5 EB pro Monat im Jahr 2015, einem CAGR von 22 Prozent (Abbildung 1). Dieses Wachstum stellt nur eine leichte Verjüngung aus der vergangenen Jahre prognostizierten Wachstumsrate für 2014 bis 2019, die 23 Prozent. Es scheint, dass das globale IP-Verkehrswachstum im 2025-Prozentbereich stabilisiert. Abbildung 1. Cisco VNI prognostiziert 194 EB pro Monat IP-Verkehr bis 2020 Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Für weitere Details über Ciscos Prognose-Methodik, siehe das Papier Cisco VNI: Prognose und Methodik, 20152020. Um das Ausmaß zu verstehen Des IP-Verkehrsvolumens, hilft es, die Zahlen in vertrauteren Ausdrücken zu betrachten: Bis 2020 wird das Gigabyte (GB) Äquivalent aller Filme jemals das globale Internet alle 2 Minuten überqueren. Weltweit erreicht IP-Verkehr im Jahr 2020 511 Terabits pro Sekunde (Tbps), das entspricht 142 Millionen Menschen, die täglich High-Definition - (HD-) Video gleichzeitig streamen. Der globale IP-Verkehr im Jahr 2020 entspricht 504 Milliarden DVDs pro Jahr, 42 Milliarden DVDs pro Monat oder 58 Millionen DVDs pro Stunde. Der Internet-Verkehr hat in den letzten zwei Jahrzehnten ein dramatisches Wachstum erfahren. Vor mehr als 20 Jahren, 1992, führten globale Internetnetze rund 100 GB Verkehr pro Tag. Zehn Jahre später, im Jahr 2002, belief sich der globale Internetverkehr auf 100 Gigabytes pro Sekunde (GBPS). Im Jahr 2015 erreichte der globale Internet-Verkehr mehr als 20.000 GBP. Tabelle 1 gibt einen Überblick über die historischen Benchmarks für den gesamten Internetverkehr. Tabelle 1: Cisco VNI ForecastHistorischer Internet-Kontext Quelle: Cisco VNI, 2016 Das Wachstum der Pro-Kopf-IP und des Internetverkehrs hat in den letzten zehn Jahren eine ähnlich steile Wachstumskurve verfolgt. Weltweit wird der monatliche IP-Verkehr bis 2020 25 GB pro Kopf erreichen, von 10 GB pro Kopf im Jahr 2015 und Internet-Verkehr wird bis 2020 21 GB pro Kopf erreichen, von 7 GB pro Kopf im Jahr 2015. Vor nicht langer Zeit im Jahr 2008 , Pro Kopf Internet-Verkehr betrug 1 GB pro Monat. Im Jahr 2000 betrug die Pro-Kopf-Internet-Verkehr 10 Megabyte (MB) pro Monat. Die folgenden Abschnitte erkunden die Trends, die zum weiteren Wachstum des globalen IP-Verkehrs beitragen. Trend 1: Fortschritte im Mix von Geräten und Verbindungen Abbildung 2 zeigt, dass weltweit Geräte und Verbindungen (10 Prozent CAGR) schneller wachsen als sowohl die Bevölkerung (1,1 Prozent CAGR) als auch Internetbenutzer (6,5 Prozent CAGR). Dieser Trend beschleunigt den Anstieg der durchschnittlichen Anzahl von Geräten und Verbindungen pro Haushalt und pro Internetbenutzer. Jedes Jahr werden verschiedene neue Geräte in verschiedenen Formfaktoren mit erhöhten Fähigkeiten und Intelligenz eingeführt und auf dem Markt angenommen. Eine wachsende Zahl von M2M-Anwendungen, wie Smart Meter, Videoüberwachung, Überwachung des Gesundheitswesens, Transport und Paket - oder Asset-Tracking, tragen wesentlich zum Wachstum von Geräten und Verbindungen bei. Bis 2020 werden M2M-Verbindungen 46 Prozent der gesamten Geräte und Verbindungen sein. Abbildung 2. Global Devices und Connections Growth Figures (n) beziehen sich auf 2015, 2020 Geräte-Aktie. Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 M2M-Verbindungen werden die am schnellsten wachsende Kategorie, wächst fast 2,5-fach im Prognosezeitraum, bei 20percent CAGR, auf 12,2 Milliarden Verbindungen bis 2020. Smartphones wird die zweite am schnellsten wachsen, mit 13 Prozentiger CAGR (Anstieg um den Faktor 1,8). Verbundene Fernsehgeräte (einschließlich Flachbildschirme, Set-Top-Boxen, digitale Medienadapter DMAs, Blu-ray Disc-Player und Spielekonsolen) werden mit 12 Prozent CAGR nahezu am schnellsten wachsen, bis auf 3,1 Milliarden bis 2020 (Über einen 2-prozentigen Rückgang) über den Prognosezeitraum zurückgehen. Allerdings wird es mehr PCs als Tabletten bis zum Ende des Jahres 2020 (1,35 Milliarden PCs vs 785 Millionen Tabletten). Bis 2020 wird der Konsumentenanteil der gesamten Geräte, einschließlich der festen und mobilen Geräte, 74 Prozent sein, wobei das Unternehmen die restlichen 26 Prozent beansprucht. Der Konsumentenanteil wird mit einer geringfügig niedrigeren Rate bei 9,5 Prozent CAGR im Verhältnis zum Geschäftssegment wachsen, das bei 12 Prozent CAGR wachsen wird. Weitere Einzelheiten zum Wachstum von Geräten und Verbindungen in Wohn-, Konsumenten - und Geschäftsbereichen finden Sie im Cisco VNI Service Adoption Forecast Highlights-Tool. Weltweit wächst die durchschnittliche Anzahl der Geräte und Verbindungen pro Kopf von 2 im Jahr 2015 auf 3,2 im Jahr 2020 (Tabelle 2). Tabelle 2. Durchschnittliche Anzahl der Geräte und Verbindungen pro Kopf Quelle: Cisco VNI, 2016 Unter den Ländern, die den höchsten Durchschnitt der Pro-Kopf-Geräte und Verbindungen bis 2020 haben, sind die USA (12,3), Südkorea (12,2) und Japan (11,9). Die veränderte Mischung von Geräten und Verbindungen und das Wachstum in Multidevice-Besitz wirkt sich auf den Verkehr aus und kann in dem sich ändernden Gerätebeitrag zum gesamten IP-Verkehr gesehen werden. Am Ende des Jahres 2015 stammten 47 Prozent des IP-Verkehrs und 37 Prozent des privaten Internet-Verkehrs aus Nicht-PC-Geräten. Bis 2020 werden 71 Prozent der IP-Verkehr und 71 Prozent der Verbraucher Internet-Verkehr von Nicht-PC-Geräten stammen (Abbildung 3). Abbildung 3. Globaler IP-Verkehr nach Geräten Figuren (n) beziehen sich auf 2015, 2020 Geräte-Freigabe. Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Wie im Fall von Mobilfunknetzen können Videogeräte einen Multiplikatoreffekt auf den Verkehr haben. Ein Internet-fähiges HD-Fernsehen, das 45 Minuten Inhalt pro Tag aus dem Internet zieht, würde so viel Internet-Verkehr generieren wie ein gesamter Haushalt heute. Mit dem Wachstum der Video-Betrachtung auf Smartphones und Tablets wächst der Verkehr von diesen Geräten als Prozentsatz der gesamten Internet-Verkehr. Tablets werden bis 2020 15 Prozent des gesamten weltweiten Internetverkehrs ausmachen, von 9 Prozent im Jahr 2015. Smartphones werden bis 2020 37 Prozent des globalen Internetverkehrs ausmachen, von 11 Prozent im Jahr 2015 (Abbildung 4). Abbildung 4. Globaler Internet-Verkehr nach Gerätetypen Die Zahlen (n) beziehen sich auf 2015, 2020 Gerätefreigabe. Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Die Videoauswirkung der Geräte auf den Datenverkehr ist aufgrund der Einführung von Ultra-High-Definition (UHD) oder 4K, Video-Streaming ausgeprägter. Diese Technologie hat einen solchen Effekt, weil die Bitrate für 4K-Video bei etwa 18 Mbps mehr als doppelt so hoch ist wie die HD-Video-Bitrate und neunmal mehr als die Standard-Definition (SD) - Video-Bitrate. Wir schätzen, dass bis 2020 40 Prozent der installierten Flachbildschirm-TV-Geräte UHD werden, von 8 Prozent im Jahr 2015 (Abbildung 5). Abbildung 5: Erhöhung der Video-Definition: Bis 2020 wird mehr als 40 Prozent der angeschlossenen Flachbildschirme 4K Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 UHD (oder 4K) IP VoD wird für 21 Prozent des weltweiten VoD-Verkehr Im Jahre 2020 (Fig. 6). Abbildung 6. Globale 4K-Video-Verkehrszahlen (n) beziehen sich auf 2015, 2020 Verkehrswerte. Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 2: IPv6-Adoption ermöglicht Internet von allem Konnektivität Der Übergang von einer IPv4-Umgebung zu einer IPv6-Umgebung macht hervorragende Fortschritte, mit einer Erhöhung der IPv6-Gerätekapazitäten, der Content-Aktivierung und der Implementierung von IPv6 Ihre Netzwerke. Diese Entwicklungen sind besonders wichtig, weil Asien, Europa, Nordamerika und Lateinamerika ihre IPv4-Allotments bereits ausgeschöpft haben und Afrika voraussichtlich bis 2018 ihre Anteile ausschöpfen wird. Tabelle 3 zeigt die prognostizierten Erschöpfungsdaten per Mai 2016 nach Angaben der Region Internet-Registrierungen (RIR). Tabelle 3. IPv4-Adressen-Erschöpfungstermine Regionale Internetregistrierungen Auf der Grundlage der VNI-IPv6-fähigen Geräteanalyse schätzt die Prognose, dass weltweit bis 2020 fast 13 Milliarden IPv6fähige feste und mobile Geräte bis zu fast 4 Milliarden im Jahr 2015 eine CAGR von 27 Prozent. 48 Prozent aller Festnetz - und Mobilfunknetze werden bis 2020 IPv6-fähig sein (von 23 Prozent im Jahr 2015) (Abbildung 7). Diese Schätzung basiert auf der Fähigkeit des Geräts und der Netzwerkverbindung, IPv6 zu unterstützen, und ist keine Projektion aktiver IPv6-Verbindungen. Die IPv6-Fähigkeit des mobilen Geräts wird basierend auf der OS-Unterstützung von IPv6 und den Schätzungen der Mobilfunk-Infrastrukturtypen, mit denen das Gerät eine Verbindung herstellen kann (3.5-Generation 3.5G oder höher), bewertet IPv6 und eine Einschätzung der Fähigkeit der privaten Kundenanlagen (CPE) oder Business Router zur Unterstützung von IPv6, abhängig vom Endgerät-Endgerät. Abbildung 7. Globale IPv6-fähige Geräte und Verbindungen Vorhersage 20152020 Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Weltweit werden 90 Prozent der Smartphones und Tablets bis 2020 IPv6-fähig sein, von 60 Prozent im Jahr 2015. Weltweit wird es sein 5,8 Milliarden IPv6-fähige Smartphones und Tablets bis 2020 von 2,1 Milliarden im Jahr 2015. Bis 2020 werden 30 Prozent der M2M-Verbindungen IPv6-fähig sein und 3,7 Milliarden erreichen, ein 67 Prozent CAGR. Laut der Weltweiten IPv6-Launch-Organisation im Mai 2016 setzen Festnetz - und Mobilfunknetzbetreiber weltweit IPv6 ein und berichten über eine bemerkenswerte IPv6-Datenverkehrsgenerierung. Rumänien RCS amp RDS berichtet fast 12 Prozent, berichtet Frances Free Telecom 22 Prozent, berichtet KDDI fast 28 Prozent, berichtete Comcast 45 Prozent, sagte ATampT 59 Prozent, und Verizon Wireless berichtete 69 Prozent Bereitstellung. Nach Google, im Mai 2016 der Prozentsatz der Nutzer, die Zugriff auf Google über IPv6 ist etwa 11 Prozent. Unter diesen Branchenentwicklungen ist die VNI-Prognose eine Bemühung, den potenziellen IPv6-Netzwerkverkehr zu schätzen, der erzeugt werden könnte, wenn ein Prozentsatz von IPv6-fähigen Geräten aktiv an ein IPv6-Netzwerk angeschlossen wird, da der geschätzte globale Durchschnitt für den monatlichen Datenverkehr pro Gerätetyp liegt . Wenn bis zu 2020 60 Prozent der IPv6-fähigen Geräte aktiv mit einem IPv6-Netzwerk verbunden sind, schätzt die Prognose, dass der weltweite IPv6-Verkehr 55 EB pro Monat oder 34 Prozent des gesamten Internetverkehrs betragen würde (Abbildung 8). Diese erste Einschätzung des potenziellen IPv6-Datenverkehrs basiert auf den Annahmen, dass die IPv6-Gerätefähigkeit, die IPv6-Content-Aktivierung und die IPv6-Netzwerk-Implementierung Schritt halten werden. Abbildung 8: Projizierte globale feste und mobile IPv6-Verkehrsprognose 20152020 Quelle: Cisco VNI Global IP Traffic Forecast, Mit aktuellen Trends, und kann sogar beschleunigen während der Prognosezeitraum. In Anbetracht der Interdependenz dieser Variablen könnten Prognoseannahmen einer Verfeinerung unterworfen sein, wie unsere Analyse fortsetzt. Content Provider sind auch in Bewegung, um die IPv6-Aktivierung ihrer Websites und Dienste zu erhöhen. Laut Cisco IPv6 Labs. Bis zum Jahr 2020 die Inhalte über IPv6 werden etwa 35 Prozent. Es kann jedoch variieren je nach der Popularität von Websites über Regionen und Länder. Darüber hinaus haben spezifische Länderinitiativen und Content-Provider-Implementierungen die lokale Erreichbarkeit der IPv6-Inhalte positiv beeinflusst. Insgesamt ist die Wahrscheinlichkeit, dass ein erheblicher Teil des Internet-Datenverkehrs über IPv6-Netzwerke generiert wird, für Netzbetreiber, Inhaltsanbieter und Endbenutzer eine große Chance, die Skalierbarkeit und Leistungsvorteile von IPv6 zu erlangen und das Internet von Everything (IoE) zu ermöglichen. Trend 3: M2M-Anwendungen über viele Branchen beschleunigen IoE-Wachstum Das IoE-Phänomen, in dem Menschen, Prozesse, Daten und Dinge mit dem Internet und miteinander verbunden sind, zeigt konkretes Wachstum. Weltweit werden die M2M-Verbindungen um das 2,5-fache wachsen, von 4,9 Milliarden im Jahr 2015 auf 12,2 Milliarden bis 2020 (Abbildung 9). Für jedes Mitglied der Weltbevölkerung werden bis 2020 1.6 M2M-Verbindungen vorhanden sein. Abbildung 9. Globale M2M-Verbindungswachstum Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Verbundene Heimanwendungen wie Heimautomation, Heimsicherheit und Videoüberwachung, verbunden weiß Produkte und Tracking-Anwendungen, wird bis 2020 47 Prozent oder nahezu die Hälfte der gesamten M2M-Verbindungen repräsentieren (Abbildung 10). Verbundenes Gesundheitswesen, mit Anwendungen wie Gesundheitsmonitoren, Medizinspendern, First-Responder-Konnektivität und Telemedizin, wird das am schnellsten wachsende Branchensegment mit 49 Prozent CAGR sein. Verbundene Autoanwendungen haben das zweitschnellste Wachstum bei 37 Prozent CAGR. Chips für Haustiere und Viehbestand, digitale Gesundheitsmonitore und zahlreiche andere M2M-Dienste der nächsten Generation fördern dieses Wachstum. Abbildung 10. Globales M2M-Anschlusswachstum nach Industrien Andere umfassen Landwirtschaft, Bau und Notdienste. Obwohl die Zahl der Verbindungen um das Dreifache wächst, wird der globale M2M-IP-Verkehr im gleichen Zeitraum von einem EB pro Monat (1,4 Prozent des weltweiten IP-Verkehrs) auf 6,3 EB um sechs Mal sinken 2020 (3,2 Prozent des globalen IP-Verkehrs siehe Abbildung 11). Aufgrund des zunehmenden Einsatzes von Videoanwendungen auf M2M-Verbindungen und des verstärkten Einsatzes von Anwendungen wie Telemedizin und intelligente Fahrzeugnavigationssysteme, die eine höhere Bandbreite und geringere Latenz erfordern, steigt der Verkehrsaufkommen schneller als die Anzahl der Verbindungen. Abbildung 4: Dienstleistungs-Adoptionstendenzen: Residential, Consumer Mobile und Business Services Global Residential Services: Video wächst weiter zwischen 2014 und 2015 Das höchste Wachstum geschah auf der Internetseite im Online-Gaming mit einem 15-prozentigen Wachstum im Jahresvergleich (YoY). Social Networking war der am weitesten verbreitete Wohn-Internet-Service mit einem Wachstum von 8,5 Prozent und wuchs von 1,3 Milliarden Nutzern im Jahr 2014 auf 1,4 Milliarden Nutzer im Jahr 2015. Bis 2020 werden digitales Fernsehen und soziale Netzwerke die beiden Dienste mit den höchsten Durchdringungsraten sein , Mit 87 Prozent bzw. 76 Prozent. Das schnellste Wachstum wird aus zeitverzögerten TV-Diensten wie dem Personal Video Recorder (PVR) und digitalen Videorekordern (DVR) mit 7 Prozent CAGR kommen. Online-Gaming (5,3 Prozent CAGR) wird die am schnellsten wachsende Internet-Internet-Service. Das Wachstum von Online-Spielen wird vor allem durch technische Verbesserungen in PCs wie Grafik, Bewegungssensorik, Gestenerkennung usw. beschleunigt (Abbildung 12). Abbildung 12. Global Residential Services Annahme und Wachstum Hinweis. Bis 2020 wird die globale Wohn-feste Internet-Bevölkerung 2,4 Milliarden werden die Zahl der globalen TV-Haushalte werden 1,8 Milliarden sein. Quelle: Cisco VNI Service Adoption Forecast, 20152020 Global Consumer Mobile Services Zwischen 2014 und 2015 stiegen alle Mobilfunkdienste für Mobilfunk, mit Ausnahme von einem, mit mehr als 10 Prozent YoY. Der stärkste Zuwachs erzielten LBS mit einem Zuwachs von 38 Prozent von einer Basis von 585 Millionen Nutzern im Jahr 2014 auf 807 Millionen im Jahr 2015. Auch im Mobile Banking und im Handel (37 Prozent) , Gefolgt von mobilen Video (35 Prozent). Regionen wie Lateinamerika (62 Prozent YoY-Wachstum) und der Mittlere Osten und Afrika (52 Prozent YoY Wachstum) hatten das schnellste Wachstum in der Verbraucher mobilen LBS. Mobile Banking und Commerce wuchs auch die schnellste in Lateinamerika, mit 49 Prozent YoY Wachstum. Mobile Video-Wachstum wurde von Mittleren Osten und Afrika, bei 43 Prozent YoY Wachstum geführt. Von 2015 bis 2020 werden sechs von acht Konsumenten-Mobilfunkdiensten mit mehr als 14 Prozent CAGR wachsen, drei werden bei mehr als 20 Prozent CAGR wachsen, und einer wird sinken. Am schnellsten wächst die Konsumenten-LBS (3,9 Prozent), gefolgt von dem mobilen Handel (22,7 Prozent). Regionen mit besonders hohen Wachstumsraten bei den mobilen Handelsdiensten sind der Mittlere Osten und Afrika, Mittel - und Osteuropa, Lateinamerika und der Asien-Pazifik, die traditionsgemäß von traditionellen Finanzinstituten des Brickand-Mortars historisch unterversorgt wurden (oder nicht erreicht wurden) (Abbildung 13 ). Abbildung 13. Global Consumer Mobile Services Annahme und Wachstum Hinweis. Bis 2020 wird die globale Konsumenten mobile Bevölkerung 5 Milliarden sein. Quelle: Cisco VNI Service Adoption Forecast, 20152020 Global Business Services Zwischen 2014 und 2015 lag das höchste Wachstum im YoY-Bereich im Geschäftsfeld LBS mit einem Anstieg um 32 Prozent von 92 Millionen Nutzern im Jahr 2014 auf 121 Millionen im Jahr 2015 In Desktop-Videokonferenzen (25 Prozent siehe Abbildung 14). Business LBS umfasst Dienstleistungen, die von Firmenkunden verwendet werden, in denen das Abonnement in der Regel vom Arbeitgeber gezahlt wird. Diese Dienstleistungen umfassen Salesforce und Field-Force-Automatisierung, Flottenmanagement usw. Wir sehen, dass Personal - oder Desktop-Videokonferenzen zunehmend raumgestützte Konferenzen ersetzen, da das Video vereinfacht und in Unified Communications-Business-Service-Angebote integriert wird. Von 2015 bis 2020 wird erwartet, dass der am schnellsten wachsende Business-Service Desktop - oder persönliche Videokonferenzen sein wird. Das Wachstum der persönlichen Videokonferenzen, insbesondere der vereinheitlichten Kommunikationsbasierten Videokonferenzen, hat sich vor kurzem aufgrund der höheren Qualität und des niedrigeren Preises neuer Dienste und Produkte beschleunigt. Es ist auch durch die Verfügbarkeit von Desktop-Video-Conferencing-Angebote, die Standalone oder integriert werden können verursacht. Darüber hinaus wird das Wachstum der mobilen Clients Video-Conferencing-Wachstum zu unterstützen. Umgekehrt zeigt die Verwendung von Web-Conferencing ohne Video einen Rückgang von 4 Prozent CAGR über den Prognosezeitraum (Abbildung 14). Abbildung 14. Global Business Services Annahme und Wachstum Hinweis. Bis 2020 wird die globale Business-Internet-Bevölkerung 2,2 Milliarden der Zahl der Business-Nutzer werden 577 Millionen werden. Quelle: Cisco VNI Service Adoption Forecast, 20152020 Für Details über alle Aspekte der Service Adoptionsstudie, verwenden Sie das Cisco VNI Service Adoption Highlights Tool. Trend 5: Anwendungen Traffic Growth Die Summe aller Formen von IP-Video, einschließlich Internet Video, IP VoD, Videodateien, die über File Sharing, Video-Streaming Gaming und Videokonferenzen ausgetauscht werden, liegt weiterhin im Bereich von 80 bis 90 Prozent des gesamten IP-Verkehrs. Weltweit wird der IP-Videoverkehr bis 2020 82 Prozent des Verkehrs ausmachen (Abbildung 15). Abbildung 15. Globaler IP-Verkehr nach Anwendungen Kategorie Zahlen (n) beziehen sich auf 2015, 2020 Verkehr Aktien. Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Die Auswirkungen der Video-Wachstum sind schwer zu übertreiben. Mit dem Video-Wachstum entwickelt sich der Internet-Verkehr aus einem relativ stabilen Verkehr (charakteristisch für Peer-to-Peer-P2P-Verkehr) zu einem dynamischeren Verkehrsmuster. Im vergangenen Jahr haben Dienstleister eine deutliche Zunahme des Verkehrs im Zusammenhang mit Gaming-Downloads beobachtet. Neuere Konsolen wie die Xbox One und PlayStation 4 verfügen über ausreichend Onboard-Speicher, um Spielern zu ermöglichen, neue Spiele herunterzuladen, anstatt sie auf Disc zu kaufen. Diese grafisch intensiven Spiele sind große Dateien, und Gaming-Downloads sind bereits 2 Prozent der Verbraucher festen Internet-Verkehr, und wird bis 4 Prozent der Verbraucher festen Internet-Verkehr bis 2020 zu erreichen. Darüber hinaus treten diese Downloads während der Peak-Nutzung Perioden auftreten, mit Gaming-Downloads erreichen Bis zu 10 Prozent des Verkehrsaufkommens. Auswirkungen von Video auf Traffic Symmetry Mit Ausnahme von Kurzform Video-und Video-Aufruf haben die meisten Formen der Internet-Video nicht über eine große Upstream-Komponente. Infolgedessen wird Verkehr nicht mehr symmetrisch, eine Situation, die viele erwarteten, als Benutzer - erzeugter Inhalt zuerst populär wurde. Die Entstehung von Abonnenten als Content-Produzenten ist ein äußerst wichtiges soziales, wirtschaftliches und kulturelles Phänomen, aber die Abonnenten verbrauchen noch viel mehr Video als sie produzieren. Der vorgelagerte Verkehr ist seit einigen Jahren leicht rückläufig. Es scheint wahrscheinlich, dass der private Internet-Verkehr für die nächsten Jahre asymmetrisch bleibt. Allerdings könnten zahlreiche Szenarien zu einer Erhöhung der Symmetrie führen, zum Beispiel: Content Provider und Distributoren könnten P2P als Distributionsmechanismus annehmen. Seit vielen Jahren ist P2P ein kostengünstiges Content Delivery System (CDS), doch die meisten Anbieter und Distributoren haben sich für den Direktvertrieb entschieden, mit Ausnahme von Anwendungen wie PPStream und PPLive in China Bieten Live-Video-Streaming über P2P und haben großen Erfolg gehabt. Wenn Content-Anbieter in anderen Regionen folgen, könnte der Verkehr schnell hochsymmetrisch werden. High-End-Video-Kommunikation könnte beschleunigen, erfordert symmetrische Bandbreite. PC-to-PC-Video-Aufruf gewinnt an Dynamik, und die naszierende mobile Video-Calling-Markt scheint zu versprechen. Wenn High-End-Video-Anrufe populär werden, könnte der Verkehr auf größere Symmetrie zu bewegen. Wenn Dienstanbieter weitreichende Upstream-Bandbreite bereitstellen, werden Anwendungen, die Upstream-Kapazität verwenden, angezeigt. Trend 6: Cord-Cutting-Analyse Im Zusammenhang mit der VNI-Prognose bezieht sich Cord-Cutting auf die Tendenz, in der herkömmliche und abonnierte Fernsehsendungen zunehmend durch andere Videobetrachtungen wie Online - und mobiles Video, die verfügbar sind, ersetzt werden Zu den Zuschauern durch feste und mobile Internetverbindungen. Wir sehen eine Tendenz, in der das Wachstum des digitalen Fernsehdienstes, der das Fernsehen auf allen digitalen Plattformen anzeigt (Kabel, IPTV, Satellit usw.), im Vergleich zum mobilen Video deutlich langsamer wächst (Abbildung 16). Dieser Trend ist stärker ausgeprägt in Regionen wie Nordamerika und Westeuropa, wo die Durchdringung des digitalen Fernsehens bereits hoch ist. Online-Video, das wir gefunden haben, war schneller wachsen, bis zum letzten Jahr, wächst jetzt fast auf Augenhöhe mit digitalen Fernsehen. Auch in aufstrebenden Regionen sind mobile Video-Wachstumsraten sogar noch höher, da diese Regionen über feste Konnektivität überspringen. Abbildung 16. Mobile Video wächst schnellste Online-Video und Digital-TV wachsen ähnlich Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Ein weiterer Faktor, der diesen Trend unterstützt, ist, dass die insgesamt adressierbaren Märkte für diese DiensteWohn-Internet-Nutzer, Verbraucher mobile Nutzer und insgesamt TV - Für Digital-TV-Haushalte) zeigen signifikant unterschiedliche Wachstumsmuster (Abbildung 17). Internetnutzern wird erwartet, dass sie bei einem CAGR von fast 3,2 Prozent und Konsumenten mobile Nutzer mit 2,8 Prozent, während gleichzeitig die Zahl der TV-Haushalte ist Flattening mit einem mageren 1,8 Prozent prognostiziert CAGR. Abbildung 17. Wachstum der weltweiten Internetnutzer im Vergleich zum Wachstum der globalen TV-Haushalte Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Auch wenn wir uns an Internetgeräten wie digitalen Medienadaptern (DMAs) anschauen, finden wir das, obwohl sie nur repräsentieren 9 Prozent aller mit dem Internet verbundenen Set-Top-Boxen (STBs), darunter Dienstanbieter-STBs, Spielekonsolen und direkt verbundene Internet-TV-Geräte bis 2020 werden 32 Prozent des weltweiten Internet-STB-Verkehrs ausmachen. Diese Tendenz zeigt erneut, dass die STBs, die von den Dienstanbietern für den Internet-Zugang im Allgemeinen und für Video-spezifisch verwaltet werden, zunehmend weniger stark vertreten sind (Abbildung 18). Abbildung 18. Wachstum in globalen digitalen Medien Adaptern DMAs umfassen Geräte wie Roku, Apple TV, Chromecast, etc. Quelle: Cisco VNI Global IP Traffic Forecast, 20152020 Aus der Verkehrssituation erwarten wir, dass im Durchschnitt ein Haushalt, der noch auf linear ist TV wird viel weniger Verkehr erzeugen als ein Haushalt, der das Kabel abgeschnitten hat und auf Internet-Video angewiesen ist (Abbildung 19). Ein kabelschneidender Haushalt erzeugt im Jahr 2016 102 GB pro Monat, verglichen mit 49 GB pro Monat für einen durchschnittlichen Haushalt. Dieser Unterschied tritt auf, weil lineares Fernsehen viel weniger Verkehr erzeugt (ein Strom von Video, der über zahlreiche lineare TV-Haushalte gemeinsam genutzt wird) als Internet-Video, das Unicast zu jedem Internet-Videogerät ist. Figure 19. Global Cord Cutting Generates Double the Traffic Source: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 7: Security Analysis Users expect their online experience to be always available and always secureand for their personal and business assets to be safe. Annual security reports for 2016 from industry giants in the security space highlight the need for increased focus on cybercrimes, data breaches and espionage, and mitigation strategies (Figure 20). Figure 20. SecurityIndustry Top of Mind The last several years have been easily the most eventful period from a security threat perspective, with many serious data breaches that have been discussed widely in the media. There were a total of 780 breaches with a total of nearly 178 million records stolen in 2015. The number of records stolen per data breach averaged 228 thousand in 2015, according to 2015 data breach statistics from IDT911. The average cost paid for each sensitive lost or stolen record increased 6 percent from 2015 to 2016, according to a joint study by IBM and Ponemon Institute. More secure Internet servers leads to a large footprint of security and authentication, better serving end users with secure transactions and communication. The percentage of secure Internet servers that conduct encrypted transactions over the Internet using Secure Sockets Layer (SSL) compared to the total number of web-facing servers depicts the nature of the secure footprint. Western Europe led with the number of secure Internet servers per 1 million people with 50 percent, followed by Central and Eastern Europe with 29 percent, North America with 27 percent, and Asia Pacific with around 23 percent. The average number of breaches was highest in Asia Pacific organizations and lowest in U. K. and U. S. enterprises in 2015, according to a recent study published by McAfee. Sixty percent of data stolen was through web protocols, file transfer and tunneling protocols, or email. Two-thirds of breaches involved traditional corporate networks, and cloud break-ins accounted for the remaining one-third, according to McAfee and LemonFish (Figure 21). Figure 21. How Is Data being Breached Source: McAfee, Lemonfish, Cisco VNI 2016 Frequency of distributed denial-of-service (DDoS) attacks has increased more than 2.5 times over the last 3 years, according to Arbor Networks. DDoS attacks are increasing at roughly the same rate as traffic. Peak DDoS attack size (Gbps) is increasing in a linear trajectory, with peak attacks reaching 300, 400, and 500 Gbps respectively, in 2013, 2014, and 2015, at about 10 to 15 percent per year. DDoS attacks can represent up to 10 percent of a countrys total Internet traffic while they are occurring. The average size of DDoS attacks is increasing steadily and approaching 1 Gbps, enough to take most organizations completely off line. In 2015 the top motivation behind DDoS attacks was criminals demonstrating attack capabilities, with gaming and criminal extortion attempts in second and third place, respectively. DDoS attacks account for more than 5 percent of all monthly gaming-related traffic and more than 30 percent of gaming traffic while they are occurring. The events from 2015 and the first quarter of 2016 once again demonstrated that the attackers are increasing their computing resources to perform DDoS attacks. Amplification attackers, who have tools for carrying out a DDoS attack, exploit vulnerabilities in the network and compute resources. With the growth of the IoE and spread of vulnerable devices and traditional PCs, the abundance of configuration drawbacks with applications can be targeted. Security vendors continue to ensure these attacks are financially unviable for the cybercriminals. Globally the number of DDoS attacks grew 25 percent in 2015 and will increase 2.6-fold to 17 million by 2020 (Figure 22). Figure 22. Global DDoS Attacks Forecast, 2015-2020 Figures (n) refer to 2015, 2020 traffic shares. Source: Cisco VNI Global IP Traffic Forecast, 2015-2020 Trend 8: Impact of Accelerating Speeds on Traffic Growth Broadband speed is a crucial enabler of IP traffic. Broadband-speed improvements result in increased consumption and use of high-bandwidth content and applications. The global average broadband speed continues to grow and will nearly double from 2015 to 2020, from 24.7 Mbps to 47.7 Mbps. Table 4 shows the projected broadband speeds from 2015 to 2020. Several factors influence the fixed broadband-speed forecast, including the deployment and adoption of fiber to the home (FTTH), high-speed DSL, and cable broadband adoption, as well as overall broadband penetration. Among the countries covered by this study, Japan, South Korea, and Sweden lead within the VNI countries in terms of broadband speed largely because of their wide deployment of FTTH. Table 4. Fixed Broadband Speeds (in Mbps), 20152020 Source: Cisco VNI, 2016 Consider how long it takes to download an HD movie at these speeds: at 10 Mbps, it takes 20 minutes at 25 Mbps, it takes 9 minutes but at 100 Mbps, it takes only 2 minutes. High-bandwidth speeds will be essential to support consumer cloud storage, making the download of large multimedia files as fast as a transfer from a hard drive. Table 5 shows the percentage of broadband connections that will be faster than 10 Mbps, 25 Mbps, and 100 Mbps by region. Table 5. Broadband Speed Greater Than 10 Mbps, 20152020 Greater Than 10 Mbps Greater Than 25 Mbps Greater Than 100 Mbps Central and Eastern Europe Middle East and Africa Source: Cisco VNI, 2016 There is a strong correlation between experienced speeds and number of video minutes viewed per viewer (Figure 23). As speeds increase in each country covered in the study, the number of video minutes per viewer also increases. Figure 23. Increase in Experienced Speeds (Mbps) Increases Internet Video Viewership (Minutes)2016 Source: Cisco VNI Global IP Traffic Forecast, 20152020 Globally, the average mobile network connection speed in 2015 was 2.0 Mbps. The average speed will more than double and will be 6.5 Mbps by 2020. Smartphone speeds, generally third-generation (3G) and later, are currently nearly three times higher than the overall average. Smartphone speeds will nearly double by 2020, reaching 12.5 Mbps. Anecdotal evidence supports the idea that overall use increases when speed increases, although there is often a delay between the increase in speed and the increased use, which can range from a few months to several years. The reverse can also be true with the burstiness associated with the adoption of tablets and smartphones, where there is a delay in experiencing the speeds that the devices can support. The Cisco VNI Forecast relates application bit rates to the average speeds in each country. Many of the trends in the resulting traffic forecast can be seen in the speed forecast, such as the high growth rates for developing countries and regions relative to more developed areas (Table 6). Table 6. Projected Average Mobile Network Connection Speeds (in Mbps) by Region and Country Source: Cisco VNI Mobile, 2016 Current and historical speeds are based on data from Ooklas Speedtest. Forward projections for mobile data speeds are based on third-party forecasts for the relative proportions of 2G, 3G, 3.5G, and 4G among mobile connections through 2020. A crucial factor promoting the increase in mobile speeds over the forecast period is the increasing proportion of fourth-generation (4G) mobile connections. The impact of 4G connections on traffic is significant, because 4G connections, which include mobile WiMAX and Long-Term Evolution (LTE), generate a disproportionate amount of mobile data traffic. Wi-Fi Speeds from Mobile Devices Globally, Wi-Fi connection speeds originated from dual-mode mobile devices will nearly double by 2020. The average Wi-Fi network connection speed (10.6 Mbps in 2015) will exceed 18.5 Mbps in 2020. North America will experience the highest Wi-Fi speeds, 29 Mbps, by 2020 (Table 7). Wi-Fi speeds inherently depend on the quality of the broadband connection to the premises. The speed also depends on the Wi-Fi standard in the CPE device. The latest standard, IEEE 802.11ac, is considered a true wired complement and can enable higher-definition video streaming and services that require higher data rates. Also an important factor in the use of Wi-Fi technology is the number and availability of hotspots. Table 7. Projected Average Wi-Fi Network Connection Speeds (in Mbps) by Region and Country Source: Cisco VNI, 2016 Trend 9: Mobility (Wi-Fi) Continues to Gain Momentum Globally, there will be nearly 433 million public Wi-Fi hotspots by 2020, up from 64 million hotspots in 2015, a sevenfold increase. By 2020, China will lead in total number of hotspots, followed by the United States and France. Western Europe had 45 percent of the worlds Wi-Fi hotspots share in 2015. By 2020, public Wi-Fi along with community hotspots are accounted for as well. Community hotspots or homespots are just emerging as a potentially significant element of the public Wi-Fi landscape. In this model, subscribers allow part of the capacity of their residential gateway to be open to casual use. The homespot may be provided by a broadband or other provider directly or through a partner. Asia Pacific will lead in adoption of homespots. By 2020, China will lead in total number of homespots, followed by France and Japan. Adoption of homespots has been led by Western Europe and then North America in 2015, but Asia Pacific will lead by 2020. Critical enablers of Hotspot 2.0 adoption are higher-speed Wi-Fi gateways and the adoption of the IEEE 802.11ac and 802.11n standards. Globally, the prevalence of IEEE 802.11ac, the latest Wi-Fi standard, will gain momentum from 2015 through 2020. In 2015, 59.5 percent of all home Wi-Fi routers shipped globally were 802.11ac-enabled. By 2020, 96.6 percent of all home Wi-Fi routers will be equipped with 802.11ac. IEEE 802.11n, which was ratified in 2007, provides a range of speeds that allow users to view medium-resolution video streaming because of the higher throughput. The latest standard, IEEE 802.11ac, with very high theoretical speeds, is considered a true wired complement and can enable higher-definition video streaming and services with use cases that require higher data rates (Figure 24). Figure 24. Future of Wi-Fi as Wired Complement The rapid growth of mobile data traffic has been widely recognized and reported. The trend toward mobility carries over into the realm of fixed networks as well, in that an increasing portion of traffic will originate from portable or mobile devices. Figure 25 shows the growth in Wi-Fi and mobile traffic in relation to traffic from wired devices. By 2020, wired networks will account for 34 percent of IP traffic, and Wi-Fi and mobile networks will account for 66 percent of IP traffic. In 2015, wired networks accounted for the majority of IP traffic, at 52 percent Wi-Fi accounted for 43 percent and mobile or cellular networks accounted for 5 percent of total global IP traffic. Figure 25. Global IP Traffic, Wired and Wireless Wireless traffic includes Wi-Fi and mobile. Source: Cisco VNI Global IP Traffic Forecast, 20152020 Narrowing the focus to Internet traffic and excluding managed IP traffic yields a more pronounced trend. By 2020, wired devices will account for 22 percent of Internet traffic, and Wi-Fi and mobile devices will account for 78 percent of Internet traffic (Figure 26). In 2015, wired devices accounted for less than half of Internet traffic, at 38 percent. Figure 26. Global Internet Traffic, Wired and Wireless Source: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 10: Traffic-Pattern Analysis (Peak Compared to Average and CDN Uptake) Although average Internet traffic has settled into a steady growth pattern, busy-hour traffic (or traffic in the busiest 60minute period of the day) continues to grow more rapidly. Service providers plan network capacity according to peak rates rather than average rates. In 2015, busy-hour Internet traffic grew 51 percent, and average traffic grew at 29 percent. Between 2015 and 2020, global busy-hour Internet use will grow at a CAGR of 36 percent, compared with 25 percent for average Internet traffic (Figure 27). Video is the underlying reason for accelerated busy-hour traffic growth. Unlike other forms of traffic, which are spread evenly throughout the day (such as web browsing and file sharing), video tends to have a prime time. Because of video consumption patterns, the Internet now has a much busier busy hour. Because video has a higher peak-to-average ratio than data or file sharing, and because video is gaining traffic share, peak Internet traffic will grow faster than average traffic. The growing gap between peak and average traffic is amplified further by the changing composition of Internet video. Real-time video such as live video, ambient video, and video calling has a peak-to-average ratio that is higher than on-demand video. Figure 27. Busy-Hour Compared with Average Internet Traffic Growth Source: Cisco VNI Global IP Traffic Forecast, 20152020 Changes in traffic topology are being brought about by the increasing role of content delivery networks (CDNs) in data delivery. CDNs will carry 64.5 percent of total Internet traffic by 2020 (Figure 28). Although network performance is usually attributed to the speeds and latencies offered by the service provider, the delivery algorithms used by CDNs have an equal if not more significant bearing on video quality. Figure 28. Global Content Delivery Network Internet Traffic, 2015 and 2020 Source: Cisco VNI Global IP Traffic Forecast, 20152020 Speed is a critical factor in Internet traffic. When speed increases, users stream and download greater volumes of content, and adaptive bit-rate streaming increases bit rates automatically according to available bandwidth. Service providers find that users with greater bandwidth generate more traffic. In 2015, households with high-speed fiber connectivity generated 58 percent more traffic than households connected by DSL or cable broadband, globally (Figure 29). The average FTTH household generated 68 GB per month in 2015 and will generate 138 GB per month in 2020. Figure 29. Fiber-Connected Households Generate More Traffic Than Households with Other Sources of Broadband Source: Cisco VNI Global IP Traffic Forecast, 20152020 To limit the volume of traffic, service providers can institute use-based tiered pricing and data caps. On mobile networks, by looking at the use of more than 33,000 lines from Tier-1 mobile operators from 2010 to 2015, we found that monthly traffic from the top 1 percent of users is down to 18 percent of overall use compared to 52 percent in 2010, showing the effects of tiered pricing. With mobile penetration reaching a saturation point in many countries across all regions, the trend has been toward tiered plans as a way to monetize data and effectively manage or throttle the top users of traffic. On the fixed networks, data caps continue to increase to match subscribers growing appetite for video. In the United States, Tier-1 carriers are offering a variety of fair usage limits today, as high as 1 TB per month. A large provider in Japan has a 30-GB-per-day upload cap. In several countries, Netflix has a sizable percentage of the Internet video minutes and traffic. Wildcard traffic generators such as Twitch. TV, a live streaming service in which video gamers watch each other play, has established itself on many fixed networks around the world. Data caps affect a larger percentage of mobile users than fixed users. With Tier-1 carriers, approximately 12 percent of mobile users consume more than 2 GB per month (a common mobile data cap), whereas only 1.4 percent of fixed users consume more than 500 GB per month (a common fixed data cap). Other Trends to Watch Ciscos approach to forecasting IP traffic is conservative, and certain emerging trends have the potential to increase the traffic outlook significantly. Growth of smartphones as the communications hub for social media, video consumption, tracking IoEdigitization applications (et al.), as well as traditional voice. This trend demonstrates the impact that smartphones have on how consumers and businesses users access and use the Internet and IP networks. Internet gaming is seeing a resurgencethe traffic nearly doubled in 2015 and will grow seven-fold by 2020. Gaming on demand and streaming gaming platforms have been in development for several years, with many newly released in 2014 and 2015. With traditional gaming, graphical processing is performed locally on the gamers computer or console. With cloud gaming, game graphics are produced on a remote server and transmitted over the network to the gamer. If cloud gaming becomes popular, gaming could quickly become one of the largest Internet traffic categories. Virtual reality . With new hardware available to individuals, and a growing body of content to consume, virtual reality has experienced high growth in recent years. Traffic associated with virtual and augmented reality applications quadrupled in 2015 and is poised to grow 61-fold by 2020. This growth stems mainly from the download of large virtual reality content files and applications, but a significant wild card is the potential adoption of virtual reality streaming, which could raise our prediction of high-growth even higher. Immersive video . This emerging traffic type can cause significant new network design implications as it is a high-bandwidth consuming application. Social media platforms such as Facebook have launched support for spherical, or immersive video that integrates multiple camera angles to form a single video stream and can be watched from the viewers preferred perspective. It can generate bit rates 3 to 10 times greater than non-immersive HD bit rates. Video surveillance . New Internet-connected video surveillance cameras upload a constant video stream to the cloud for remote viewing. With a steady flow of video traffic from each camera, video surveillance is already having an impact on overall Internet traffic and accounts for 1.5 percent of total Internet traffic today, growing to nearly 4 percent by 2020. If such devices become mass market in the next five years, we could see video cameras generating a significantly higher volume of traffic, since Internet-enable cameras can produce up to 300 GB per camera per month for full HD-resolution monitoring of high-activity areas. For More Information For more information about the Cisco IP traffic forecast, refer to Cisco VNI: Forecast and Methodology, 20152020 and visit the other resources and updates at ciscogovni. Several interactive tools allow you to create custom highlights and forecast charts by region, country, application, and end-user segment. Refer to the Cisco VNI Highlights tool and the Cisco VNI Forecast Widget tool. For regional details about the VNI service adoption forecast, please visit the Cisco VNI SA highlights tool and Cisco VNI SA Graphing tool. Inquiries can be directed to trafficinquiriescisco . Appendix A: Cisco Global IP Traffic Forecast Table 8 shows a summary of the Cisco global IP traffic forecast. For more information and additional tables, refer to Cisco VNI: Forecast and Methodology, 20152020. Table 8. Global IP Traffic, 20152020Background photo courtesy NSSL. Last modified 29 Mar 2016 This list of Frequently Asked Questions (FAQ) has been compiled from questions asked of the SPC as well as basic tornado research information and countless scientific resources. More material will be added, time permitting. If you find a link not working or an error of any sort, please e-mail the FAQ author. The Tornado FAQ is not intended to be a comprehensive guide to tornadoes. Instead, it is a quick-reference summary of tornado knowledge, which will link you to more detailed information if you desire. Recent books from your local library or a major university library are still the deepest resource for learning about tornadoes and other severe storms so if you are doing your own research or school reports, please visit the library in person. There are many good websites with tornado information, but also, many inaccurate and unreliable ones. As with any other subject, please proceed with great caution online when investigating tornadoes. Some of the trustworthy sites are linked from the answers below. None of the links to outside websites implies any kind of commercial endorsement on the part of the SPC. The intent here is to direct you to the best tornado info available, regardless of domain. There is also a partial list of technical scientific references related to tornadoes for those with some meteorological education and training. HINWEIS . All images found in FAQ pages on this site must be public domain and not copyrighted by regulation. However, credit should be given to NOAA for use of images, unless labeled otherwise. THE BASICS ABOUT TORNADOES What is a tornado According to the Glossary of Meteorology (AMS 2000), a tornado is a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud. Literally, in order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base. Weather scientists havent found it so simple in practice, however, to classify and define tornadoes (per this essay by Doswell ). For example, the difference is unclear between an strong mesocyclone (parent thunderstorm circulation) on the ground, and a large, weak tornado. There is also disagreement as to whether separate ground contacts of the same funnel constitute separate tornadoes. Meteorologists also can disagree on precisely defining large, intense, messy multivortex circulations, such as the El Reno tornado of 2013. compared to the parent mesocyclone and surrounding winds of damaging intensity. It is well-known that a tornado may not have a visible funnel. Mobile radars also have showed that tornadoes often extend outside an existing, visible funnel. At what wind speed of the cloud-to-ground vortex does a tornado begin How close must two or more different tornadic circulations become to qualify as a one multiple-vortex tornado. instead of separate tornadoes There are no firm answers. BACK UP TO THE TOP How do tornadoes form The classic answer--warm moist Gulf air meets cold Canadian air and dry air from the Rockies--is a gross oversimplification. Most thunderstorms that form under those conditions (near warm fronts, cold fronts and drylines respectively) never make tornadoes. Even when the large-scale environment is extremely favorable for tornadic thunderstorms, as in an SPC High Risk outlook, not every thunderstorm spawns a tornado. The truth is that we dont fully understand. The most destructive and deadly tornadoes occur from supercells --which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone . Supercells can also produce damaging hail. severe non-tornadic winds, unusually frequent lightning. and flash floods . Tornado formation is believed to be dictated mainly by things which happen on the storm scale. in and around the mesocyclone. Recent theories and results from the VORTEX programs suggest that once a mesocyclone is underway, tornado development is related to temperature changes across the edge of downdraft air wrapping around the mesocyclone (the occlusion downdraft ). Mathematical modeling studies of tornado formation also indicate that it can happen without such temperature patterns and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on 3 May 1999. The details behind these theories are given in several of the Scientific References accompanying this FAQ. BACK UP TO THE TOP What direction do tornadoes come from Does the region of the US play a role in path direction Tornadoes can appear from any direction. Most move from southwest to northeast, or west to east. Some tornadoes have changed direction amid path, or even backtracked. A tornado can double back suddenly, for example, when its bottom is hit by outflow winds from a thunderstorms core. Some areas of the US tend to have more paths from a specific direction, such as northwest in Minnesota or southeast in coastal south Texas. This is because of an increased frequency of certain tornado-producing weather patterns (say, hurricanes in south Texas, or northwest-flow weather systems in the upper Midwest). BACK UP TO THE TOP Does hail always come before the tornado Rain Lightning. Utter silence Not necessarily, for any of those. Rain, wind, lightning. and hail characteristics vary from storm to storm, from one hour to the next, and even with the direction the storm is moving with respect to the observer. While large hail can indicate the presence of an unusually dangerous thunderstorm, and can happen before a tornado, dont depend on it. Hail. or any particular pattern of rain, lightning or calmness, is not a reliable predictor of tornado threat. BACK UP TO THE TOP How do tornadoes dissipate The details are still debated by tornado scientists. We do know tornadoes need a source of instability (heat, moisture, etc.) and a larger-scale property of rotation ( vorticity ) to keep going. There are a lot of processes around a thunderstorm which can possibly rob the area around a tornado of either instability or vorticity. One is relatively cold outflow --the flow of wind out of the precipitation area of a shower or thunderstorm. Many tornadoes have been observed to go away soon after being hit by outflow. For decades, storm observers have documented the death of numerous tornadoes when their parent circulations ( mesocyclones ) weaken after they become wrapped in outflow air--either from the same thunderstorm or a different one. The irony is that some kinds of thunderstorm outflow may help to cause tornadoes, while other forms of outflow may kill tornadoes. BACK UP TO THE TOP Do tornadoes really skip Not in a literal sense, despite what you may have read in many older references, news stories, or even damage survey reports. By definition (above), a tornado must be in contact with the ground. There is disagreement in meteorology over whether or not multiple ground contacts of the same vortex or funnel cloud mean different tornadoes (a strict interpretation). In either event, stories of skipping tornadoes usually mean There was continuous contact between vortex and ground in the path, but it was too weak to do damage Multiple tornadoes happened, but there was no survey done to precisely separate their paths (very common before the 1970s) or There were multiple tornadoes with only short separation, but the survey erroneously classified them as one tornado. BACK UP TO THE TOP What happens when two tornadoes come together That is more unusual than it seems, because most video that seems to show tornadoes merging actually involves either one tornado, or one among multiple subvortices. going behind another. On those very rare occasions when tornadoes do merge, it usually involves a larger and stronger tornado that simply draws in and absorbs the lesser circulation, then keeps on going. On 24 May 2011, the author of this FAQ witnessed and photographed a merger of a long-lived, violent tornado with a satellite tornado that had grown about as large and strong, based on mobile Doppler-radar data. That rare and maybe unique event is documented in this formal journal paper. BACK UP TO THE TOP How long does a tornado last Tornadoes can last from several seconds to more than an hour. The longest-lived tornado in history is really unknown, because so many of the long-lived tornadoes reported from the early-mid 1900s and before are believed to be tornado series instead. Most tornadoes last less than 10 minutes. The average distance tornadoes have traveled (based on path length data since 1950) is about 3-12 miles. BACK UP TO THE TOP What is the purpose for a tornado To oversimplify this a bit, a tornado (or any other atmospheric vortex) is the most efficient way to move air from one part of the atmosphere to another on its size and time scale. In fluid flow (whether gas or liquid), a vortex often forms when some kind of instability difference exists between one part of the fluid and another, and that difference is strong enough that the fluid needs to move quickly to restore more stable conditions again. This happens on many scales, from huge midlatitude cyclones to hurricanes, supercells, tornadoes and backyard whirlwinds--even the vortex that forms above a bathtub drain. Most thunderstorms apparently do not need a vortex as intense and efficient at moving air as a tornado, to fulfill their own function of transporting a plume of initially unstable air from the lower atmosphere to higher levels. Why some thunderstorms go far enough to require a tornados assistance is a matter of great speculation and debate in meteorology. For those with a strong scientific background, Chuck Doswell offers some in-depth insights on possibilities for the role of tornadoes. BACK UP TO THE TOP How close to a tornado does the barometer drop. And how far does it drop It varies. A barometer can start dropping many hours or even days in advance of a tornado if there is low pressure on a broad scale moving into the area. Strong pressure falls will often happen as the mesocyclone (parent circulation in the thunderstorm) moves overhead or nearby. The biggest drop will be in the tornado itself, of course. It is very hard to measure pressure in tornadoes since most weather instruments cant survive. A few low-lying, armored probes called turtles have been placed successfully in tornadoes. This includes one deployment on 15 May 2003 by the late Tim Samaras, who recorded pressure fall of over 40 millibars through an unusually large tornado. On 24 June 2003, another of Tims probes recorded a 100 millibar pressure plunge in a violent tornado near Manchester, SD (National Geographic report ). On 21 April 2007, a private storm-chase vehicle--outfitted with fully functional, scientific-grade instruments--measured the current record pressure drop of 194 millibars in Tulia, TX. Despite those spectacular results, and a few fortuitous passes over barometers through history, we still do not have a database of tornado pressures big enough to say much about average tornado pressures or other barometric characteristics. That has to be left to the world of computer simulations of tornadoes. BACK UP TO THE TOP What is a waterspout A waterspout is a tornado over water --usually meaning non-supercell tornadoes over water. Waterspouts are common along the southeast U. S. coast--especially off southern Florida and the Keys--and can happen over seas, bays and lakes worldwide. Although waterspouts are always tornadoes by definition they dont officially count in tornado records unless they hit land. They are smaller and weaker than the most intense Great Plains tornadoes, but still can be quite dangerous. Waterspouts can overturn boats. damage larger ships, do significant damage when hitting land, and kill people. The National Weather Service will often issue special marine warnings when waterspouts are likely or have been sighted over coastal waters, or tornado warnings when waterspouts can move onshore. BACK UP TO THE TOP How are tornadoes in the northern hemisphere different from tornadoes in the southern hemisphere The sense of rotation is usually the opposite. Most tornadoes (but not all) rotate cyclonically . which is counterclockwise in the northern hemisphere and clockwise south of the equator. Anticyclonic tornadoes (clockwise-spinning in the northern hemisphere) have been observed, however--usually in the form of waterspouts, non-supercell land tornadoes, or anticyclonic whirls around the rim of a supercells mesocyclone. There have been several documented cases of cyclonic and anticyclonic tornadoes under the same thunderstorm at the same time. Anticyclonically rotating supercells with tornadoes are extremely rare but one struck near Sunnyvale, CA. in 1998. Two clockwise tornadoes from another anticyclonic storm struck south-central Oklahoma on 10 May 2010. Remember, cyclonic tornadoes spin counter-clockwise in the northern hemisphere, and clockwise in the southern. BACK UP TO THE TOP What is a multivortex tornado Multivortex (a. k.a. multiple-vortex) tornadoes contain two or more small, intense subvortices orbiting the center of the larger tornado circulation. When a tornado doesnt contain too much dust and debris, they can sometimes be spectacularly visible. These vortices may form and die within a few seconds, sometimes appearing to train through the same part of the tornado one after another. They can happen in all sorts of tornado sizes, from huge wedge tornadoes to narrow rope tornadoes. Subvortices are the cause of most of the narrow, short, extreme swaths of damage that sometimes arc through tornado tracks. From the air, they can preferentially mow down crops and stack the stubble, leaving cycloidal marks in fields. Multivortex tornadoes are the source of most of the old stories from newspapers and other media before the late 20th century which told of several tornadoes seen together at once. BACK UP TO THE TOP What is the original F-scale Dr. T. Theodore Fujita developed a damage scale (Fujita 1971, Fujita and Pearson 1973) for winds, including tornadoes, which was supposed to relate the degree of damage to the intensity of the wind. This scale was the result. The original F-scale should not be used anymore, because it has been replaced by an enhanced version. Tornado wind speeds are still largely unknown and the wind speeds on the original F-scale have never been scientifically tested and proven . Different winds may be needed to cause the same damage depending on how well-built a structure is, wind direction, wind duration, battering by flying debris, and a bunch of other factors. Also, the process of rating the damage itself is largely a judgment call--quite inconsistent and arbitrary (Doswell and Burgess, 1988). Even meteorologists and engineers highly experienced in damage survey techniques often came up with different F-scale ratings for the same damage. Even with all its flaws, the original F-scale was the only widely used tornado rating method for over three decades. The enhanced F-scale takes effect 1 February 2007. BACK UP TO THE TOP What is the Enhanced F-scale The Enhanced F-scale (simple table or detailed 95-page PDF ) is a much more precise and robust way to assess tornado damage than the original. It classifies F0-F5 damage as calibrated by engineers and meteorologists across 28 different types of damage indicators (mainly various kinds of buildings, but also a few other structures as well as trees). The idea is that a one size fits all approach just doesnt work in rating tornado damage, and that a tornado scale needs to take into account the typical strengths and weaknesses of different types of construction. This is because the same wind does different things to different kinds of structures. In the Enhanced F-scale, there will be different, customized standards for assigning any given F rating to a well built, well anchored wood-frame house compared to a garage, school, skyscraper, unanchored house, barn, factory, utility pole or other type of structure. In a real-life tornado track, these ratings can be mapped together more smoothly to make a damage analysis. Of course, there still will be gaps and weaknesses on a track where there was little or nothing to damage, but such problems will be less common than under the original F-scale. As with the original F-scale, the enhanced version will rate the tornado as a whole based on most intense damage within the path. There are no plans to systematically re-evaluate historical tornadoes using the Enhanced F-scale. A full PDF document on the Enhanced F-scale is online. BACK UP TO THE TOP So if the original F-scale winds were just guesses, why were they so specific Excellent question. Original F-scale winds were attached arbitrarily to the damage scale based on 12-step mathematical interpolation between the hurricane criteria of the Beaufort wind scale. and the threshold for Mach 1 (738 mph). Though the F-scale actually peaked at F12 (Mach 1), only F1 through F5 were used in practice, with F0 attached for tornadoes of winds weaker than hurricane force. The newer EF-Scale wind groupings were rooted in engineering study of wind effects, with the 3-second gust thresholds rounded to the nearest values that are divisible by 5. BACK UP TO THE TOP I heard the 1999 Oklahoma City tornado was almost F6. Is that a real level on the original F-scale Is there such a thing as EF-6 For the original F-Scale, Fujita plotted hypothetical winds higher than F5 but as mentioned in the previous answer above, they were only guesses. Even if the winds measured by portable Doppler radar (32 meters above ground level, roughly 302 mph) had been over 318 mph, the tornado still would have been rated only F5, since that is the most intense possible damage level. On the Enhanced F-scale. there is no such thing as EF6 or higher. Damage--no matter how incredible or how strong the wind--maxes out at EF-5. BACK UP TO THE TOP What is a significant tornado A tornado is considered significant if it was rated EF2 or greater on the Enhanced F scale. or at least F2 on the old F-scale. Grazulis (1993) also included killer tornadoes of any damage rating in his significant tornado database. It is important to know that those definitions are arbitrary, mainly for parsing out more intense tornadoes in scientific research. No tornado is necessarily in significant. Any tornado can kill or cause damage and some tornadoes rated less than EF2 in open areas probably could do EF2 or greater damage if they hit a sufficiently well-constructed target. BACK UP TO THE TOP Big fat tornadoes are the strongest ones, right Not necessarily. There is a statistical trend (as documented by NSSLs Harold Brooks) toward wide tornadoes having higher damage ratings. This could be related to greater tornado strength, more opportunity for targets to damage, or some blend of both. However, the size or shape of any particular tornado does not say anything conclusive about its strength. Some small rope tornadoes still can cause violent damage of EF4 or EF5 and some very large tornadoes over a quarter-mile wide have produced only weak damage equivalent to EF0 to EF1. BACK UP TO THE TOP Cant we weaken or destroy tornadoes somehow, like by bombing them or sucking out their heat with a bunch of dry ice The main problem with deploying anything packing enough energy to realistically stand a chance at affecting a tornado (e. g. hydrogen bomb) is that it would be even more deadly and destructive than the tornado itself. Lesser things (like huge piles of dry ice or smaller conventional weaponry) would be too hard to deploy in the right place fast enough, and would likely not have enough impact to affect the tornado much anyway. Imagine the legal problems one would face, too, by trying to bomb or ice a tornado, then inadvertently hurting someone or destroying private property in the process. In short--bad idea BACK UP TO THE TOP How does cloud seeding affect tornadoes Nobody knows, for certain. There is no proof that seeding can or cannot change tornado potential in a thunderstorm. This is because there is no way to know that the things a thunderstorm does after seeding would not have happened anyway . This includes any presence or lack of rain, hail, wind gusts or tornadoes. Because the effects of seeding are impossible to prove or disprove, there is a great deal of controversy in meteorology about whether it works, and if so, under what conditions, and to what extent. BACK UP TO THE TOP What does a tornado sound like That depends on what it is hitting, its size, intensity, closeness and other factors. The most common tornado sound is a continuous rumble, like a nearby train. Sometimes a tornado produces a loud whooshing sound, similar to a waterfall, or the noise of open car windows while driving very fast. Tornadoes which are tearing through densely populated areas may be producing all kinds of loud noises at once, which collectively may make a tremendous roar. Just because you may have heard a loud roar during a damaging storm does not necessarily mean it was a tornado . Any intense thunderstorm wind can produce damage and cause a roar. BACK UP TO THE TOP Where can I get tornado pictures Photographic prints of tornadoes are sold by a number of storm chasers and news outlets. You can see many interesting free weather images at photolib. noaa. govnssltornado1.html. There are also several stock photography agencies specializing in, or peddling on the side, weather photos that include tornadoes. A search engine can help you find online stock photo outfits and tornado photographs. Be wary of fakes Fake tornado photos are fairly common, especially since the early 2000s when digital photo processing and editing became relatively easy. For digital online photos, many tornado-related websites display images but since all personal photography is legally copyrighted upon creation, one legally must get permission to use them. Photos on this site and all National Oceanic and Atmospheric (NOAA) agencies, including the National Weather Service, are public domain and free to download, though credit to the agency andor source is required. BACK UP TO THE TOP Where can I get video of tornadoes Public-domain videos of tornado and other severe-storm footage are available for a reproduction fee through a video transfer service used by NOAA. Many production companies, TV stations and storm chasers have made videotapes of tornadoes available for sale as well. Try web search engines and storm chaser pages. This FAQ will not endorse any particular commercial tornado video source or tour operation. BACK UP TO THE TOP Do hurricanes and tropical storms produce tornadoes Often, but not always. There are great differences from storm to storm, not necessarily related to tropical cyclone size or intensity. Some landfalling hurricanes in the U. S. fail to produce any known tornadoes, while others cause major outbreaks. The same hurricane also may have none for awhile, then erupt with tornadoes. or vice versa Andrew (1992), for example, spawned several tornadoes across the Deep South after crossing the Gulf, but produced none during its rampage across South Florida. Katrina (2005) spawned numerous tornadoes after its devastating LAMS landfall, but only one in Florida (in the Keys). Though fewer tornadoes tend to occur with individual tropical depressions and tropical storms than hurricanes, there are notable exceptions like TS Beryl of 1994 in the Carolinas. Some tropical cyclones even produce two distinct sets of tornadoes--one around the time of landfall over Florida or the Gulf Coast, the other when well inland or exiting the Atlantic coast. Ivan (2004) produced a single-storm record of 118 tornadoes over three days, in three distinct daily cycles. BACK UP TO THE TOP Whats the nature of tornadoes in hurricanes and tropical storms Hurricane-spawned tornadoes tend to occur in small, low-topped supercells within the outer bands, NNW through ESE of the center--mainly the eastern half. There, the orientation and speed of the winds create vertical shear profiles somewhat resembling those around classic Great Plains supercells --the shear being in a shallower layer but often stronger. Occasionally a tornado will happen in the inner bands as well, but the large majority still form outside the hurricane force wind zone. Because tornado-producing circulations in hurricane supercells tend to be smaller and shorter-lived than their Midwest counterparts, they are harder to detect on Doppler radar. and more difficult to warn for. But hurricane-spawned tornadoes can still be quite deadly and destructive, as shown by the F3 tornado from Hurricane Andrew at La Place LA (1992, 2 killed) and an F4 tornado at Galveston TX from Hurricane Carla (1961, 8 killed). For more extensive documentation of knowledge and understanding about tropical cyclone tornadoes, see this formal review article. BACK UP TO THE TOP Do tropical cyclones produce waterspouts Yes. Waterspouts--tornadoes over water--have been observed in tropical systems. We dont know how many of them happen in tropical cyclones, but a majority probably are from supercells. The similarity in Doppler radar velocity signatures over water to tornado-producing cells in landfalling hurricanes suggests that it may be common, and yet another good reason for ships to steer well clear of tropical cyclones. BACK UP TO THE TOP Does tropical cyclone strength or size matter for tornadoes Often, but not always. Relatively weak hurricanes like Danny (1985) have spawned significant supercell tornadoes well inland, as have larger, more intense storms like Beulah (1967) and Ivan (2004). In general, the bigger and stronger the wind fields are with a tropical cyclone, the bigger the area of favorable wind shear for supercells and tornadoes. But supercell tornadoes (whether or not in tropical cyclones) also depend on instability, lift and moisture. Surface moisture isnt lacking in a tropical cyclone, but sometimes instability and lift are too weak. This is why tropical systems tend to produce more tornadoes in the daytime and near any fronts that may get involved in the cyclone circulation. It is also why SPC wont always have tornado watches out for every instance of a tropical cyclone affecting land. For more details, there is a set of articles on tropical cyclone tornadoes listed in the Scientific References section. For more information on hurricanes, go to the Tropical Cyclone FAQ at AOML. BACK UP TO THE TOP Who forecasts tornadoes In the U. S. only the National Weather Service (NWS) issues tornado forecasts nationwide. Warnings come from each NWS office. The Storm Prediction Center issues watches. general severe weather outlooks. and mesoscale discussions. Private weather companies sometimes issue customized tornado-risk predictions and alerts for their clients. Tornadoes in Canada are handled by the Meteorological Service of Canada. Very few other nations have specific tornado watch and warning services. BACK UP TO THE TOP How do you forecast tornadoes This is a very simple question with no simple answer Here is a very generalized view from the perspective of a severe weather forecaster: When predicting severe weather (including tornadoes) a day or two in advance, we look for the development of temperature and wind flow patterns in the atmosphere which can cause enough moisture, instability, lift, and wind shear for tornadic thunderstorms. Those are the four needed ingredients. But it is not as easy as it sounds. How much is enough of those is not a hard fast number, but varies a lot from situation to situation, and sometimes is unknown A large variety of weather patterns can lead to tornadoes and often, similar patterns may produce no severe weather at all. To further complicate it, the various computer models we use days in advance can have major biases and flaws when the forecaster tries to interpret them on the scale of thunderstorms. As the event gets closer, the forecast usually (but not always) loses some uncertainty and narrows down to a more precise threat area. At SPC, this is the transition from outlook to mesoscale discussion to watch . Real-time weather observations--from satellites, weather stations, balloon packages, airplanes, wind profilers and radar-derived winds--become more and more critical the sooner the thunderstorms are expected and the models become less important. To figure out where the thunderstorms will form, we must do some hard, short-fuse detective work: Find out the location, strength and movement of the fronts, drylines, outflows, and other boundaries between air masses which tend to provide lift. Figure out the moisture and temperatures, both near ground and aloft, which will help storms form and stay alive in this situation. Find the wind structures in the atmosphere which can make a thunderstorm rotate as a supercell. then produce tornadoes. Many supercells never spawn a tornado Make an educated guess where the most favorable combination of ingredients will be and when then draw the areas and type the forecast. For a graphical overview of the SPC forecasting process, see this poster by Steve Corfidi. BACK UP TO THE TOP Whats the threshold of forecast shear or instability for a tornado watch Whats the rotation criteria on radar for a tornado warning Modern forecasters think in terms of ingredients and processes, not check boxes and rigid thresholds. The atmosphere is much too complex for checklists to work without exception. As such, forecasters use no single threshold or criteria for either a watch or a warning. Watches and warnings instead are fast-action judgment calls, based on numerous factors. Tying in with the last question, SPC watch forecasters look for favorable overlaps of moisture, instability, lift, and vertical wind shear, for at least a few hours, over a concentrated area the size of a typical watch. How much of those ingredients It can vary greatly depending on the changing character of each event, and there is no fixed answer. Similarly, for tornado warnings, some storms with little or no radar-detected rotation can produce weak tornadoes, while other storms with frightening-looking circulations on radar displays still yield no tornado at all. Because of that variability, local NWS forecasters look at not only radar velocity, but any of many other radar products, spotter reports, analysis of the storm environment, history of existing storms, SPC guidance, short-fused weather models, and non-meteorological considerations such as potential human impact. BACK UP TO THE TOP That sounds really hard. What hardware and software tools do you use to help you forecast tornadoes The most important hardware for forecasting at the Storm Prediction Center is the human hand. Numerous hand-drawn analyses of surface and upper-air data are still performed at SPC every day so forecasters can be intimately familiar with the weather features. SPC forecasters also use high-performance computer workstations (mainly running Linux and Windows), with a huge variety of software to display the things we need to help us forecast severe weather. The variety of those things is enormous: many kinds of computer model displays. satellite image loops, radar displays. radar-wind plots. data from surface weather stations. upper air data from balloons and planes, lightning strike plots. weather data tables. multiple-source overlays. und mehr. It may sound trite but by far, the most important software in the tornado forecast process is within the human brain. The forecaster must use it to sort all that information, toss out what is not needed, properly interpret what is needed, and put it into a coherent form--all on a time deadline. Tying in with the last question, this is why one specific value or threshold of an atmospheric factor cant be used as a threshold from one situation to the next. BACK UP TO THE TOP What is needed to be a good tornado forecaster It all starts with. Motivation: Almost all severe storms forecasters are passionate about violent weather, with an intense desire to learn about and become better at predicting it. For many, this dates back into childhood--a first-hand encounter with violent storms, images on TV or in books and magazines, or even a deep attraction to storms that goes back too far to recall. Others start out in other fields or college majors, and then became fascinated with severe weather. In any case, this desire leads to. Education: Consistently good severe storms forecasters have a solid educational background in atmospheric science which allows them to understand textbook concepts of thunderstorm formation. They dont stop with their college education, either. They constantly re-educate themselves in the latest discoveries about severe thunderstorms and tornadoes--reading scientific journal articles on cutting-edge research, perhaps doing some research themselves. The understanding of storms which results lets the forecaster think of conceptual models--visualizations of what the storms will do and how. Flexibility: Because the atmosphere doesnt read textbooks or science journals, the forecaster must adapt those classroom ideas to an endless variety of day-to-day situations which may look a lot different. He or she also should be able to recognize when and why a forecast is not working out, and make the right adjustments. These skills come from. Experience: In meteorology, history never repeats itself exactly. But certain types of situations do recur, allowing the forecaster to set a mental benchmark for what to expect. From there, he or she can better decide what data will be most important to examine, and what data will not be as relevant to the situation. Experienced forecasters are able to learn how bad forecasts went wrong and how good forecasts worked each time, building a more complete mental warehouse of severe storm forecast knowledge as time passes. When the experience is continually blended with motivation, flexibility and more education, he or she will keep improving as a forecaster. BACK UP TO THE TOP What is the tornado forecast for next spring Are there going to be tornadoes in Iowa the week of next October 5 We just dont know. Tornado forecasting today and tomorrow is quite difficult already. Specific severe weather forecasting more than days in advance is little more than guessing, or using tornado climatology for the forecast area and time of year. For that reason, there is no such thing as a long range severe storm or tornado forecast. There are simply too many small-scale variables involved which we cannot reliably measure or model weeks or months ahead of time so no scientific forecasters even attempt them. Perhaps, someday, the density of weather observations and atmospheric modeling capabilities will advance enough to allow us to do severe storms forecasting many days out with some degree of accuracy better than a coin toss. We are a long, long way from that kind of forecasting BACK UP TO THE TOP What is the role of Doppler radar in tornado forecasting Each NWS forecast office uses output from at least one Doppler radar in the area to help to determine if a warning is needed. Doppler radar signatures can tell warning meteorologists a great deal about a thunderstorms structure, but usually cant see the tornado itself. This is because the radar beam gets too wide to resolve even the biggest tornadoes within a few tens of miles after leaving the transmitter. Instead, a radar indicates strong winds blowing toward and away from it in a way that tells forecasters, An intense circulation probably exists in this storm and a tornado is possible. Possible doesnt mean certain, though. That is why local forecasters must also depend on spotter reports, SPC forecast guidance on the general severe weather threat, and in-house analysis of the weather situation over the region containing thunderstorms, to make the best-informed warning decisions. BACK UP TO THE TOP What was the first successful tornado forecast Nobody knows when was the first time someone claimed a tornado would occur in an area, and it happened. But the first documented, successful tornado forecast by meteorologists was on March 25, 1948, by Air Force Capt. (later Col.) Robert Miller and Major Ernest Fawbush. After they noticed striking similarities in the developing weather pattern to others which produced tornadoes (including the Tinker AFB, OK, tornado several days before), Fawbush and Miller advised their superior officer of a tornado threat in central Oklahoma that evening. Compelled from above to issue a yesno decision on a tornado forecast after thunderstorms developed in western Oklahoma, they put out the word of possible tornadoes, and the base carried out safety precautions. A few hours later, despite the tiny odds of a repeat, the second tornado in five days directly hit the base. For more insight into this event, Charlie Crisp has transcribed the late Col. Millers recollections of the event and they are now online. BACK UP TO THE TOP What is the history of tornado forecasting Its too long and eventful to summarize here but some useful, more detailed resources include: a 2011 essay on tornado-warnng history. now available freely in the Bulletin of the AMS . as well as a timeline of SELS and SPC. and a history of the SPC that provide insight into how tornado prediction has evolved. There is also an entire book devoted to the subject: Scanning the Skies: A History of Tornado Forecasting by Marlene Bradford (hardcover - March 2001). Some libraries, bookstores and online book sellers carry this comprehensive and detailed history work. BACK UP TO THE TOP Was tornado forecasting once banned in the U. S. Yes. Before 1950, at various stages of development of the Weather Bureau, the use of the word tornado in forecasts was at times strongly discouraged and at other times forbidden, because of a fear that predicting tornadoes may cause panic. This was in an era when very little was known about tornadoes compared to today, by both scientists and the public at large. Tornadoes were, for most, dark and mysterious menaces of unfathomable power, fast-striking monsters from the sky capable of sudden and unpredictable acts of death and devastation. As the weather patterns which led to major tornado events became better documented and researched, the mystery behind predicting them began to clear--a process which still is far from complete, of course. In 1950, the Weather Bureau revoked the ban (PDF) on mentioning tornadoes in forecasts. BACK UP TO THE TOP How has SPC performed with tornado forecasting By most measures, SPC (formerly SELS, NSSFC) has improved its tornado forecasting over the past few decades. There are many ways to objectively gauge forecast performance--for example, verifying tornado watches with tornado reports and both watch types by all severe reports. The general trend from 1985 onward has been for a greater percentage of tornado watches to contain tornadoes, and for more significant (EF2-5) tornadoes to occur in watches and outlooks. BACK UP TO THE TOP How does a tornado do damage Most of the damage from a tornado happens one of two direct ways: exposure to extreme wind or impact by flying debris. In a developed area, a tornado essentially acts as a giant blender full of millions of small and large projectiles--boards, broken glass, nails, shingles, gravel, wire, cables, sheet metal, hardware, tree parts, whole trees, rocks, bricks, appliances, furniture, household items, even vehicles and large parts of houses. A dump truck thrown into a building by a nearby subvortex, for example, can do enormous damage even if the wind at the building site isnt that strong on its own. Sometimes a tornado will weaken a structure enough that parts or all of it collapses later due to structural weakness and imbalances. This is why people should not enter a heavily damaged home or other building until fire officials and an engineer can survey it. Another reason is that hazardous materials may have been released by the tornado--such as natural gas, medical waste, gasoline, other dangerous chemicals, or sewage. Such HAZMAT releases, along with live electrical wires, also can be a cause of indirect tornado damage--either chemically or through fires. Broken water pipes can cause considerable water and flood damage also. BACK UP TO THE TOP How do damage oddities happen, like wood splinters driven into bricks, phonograph records embedded in trees, or a chicken in a bottle Some oddities (like that chicken example) defy ready explanation, without direct evidence such as video from a security camera. However, embedding of objects such as straw in tires, or boards pentrating walls, trees and cars, actually happen in many tornadoes. Its all about momentum. If one throws a bullet at a wooden target, it will bounce off, even though the metal is denser and harder than the wood. If one fires that bullet from a rifle, it penetrates. Same bullet, same target. the only difference is momentum. Thats an extreme model of how it works--momentum becomes high enough to cause puncturing or embedding. This principle even works at much lower speeds with small objects into larger, harder ones. Although tornado wind doesnt reach bullet speeds (thankfully), a solid object still might penetrate a stationary one made of harder material--especially if it hits cracks, stretch marks, hollows, holes or other weaknesses in that target. Take a brick wall already stressed and stretched by an extreme tornado gust. A piece of wood or even straw can be driven into a crack or hole in that brick and stick there, or into the softer mortar that is being compromised first. At faster speeds, it might smash its own hole into the target. To study this problem and advise builders on wind resistance, Texas Techs Wind Engineering Lab has been firing boards at various construction materials (including brick walls) in their lab for decades. BACK UP TO THE TOP How is tornado damage rated The most widely used method worldwide, for over three decades, was the F-scale developed by Dr. T. Theodore Fujita. In the U. S. and probably elsewhere within a few years, the new Enhanced F-scale is becoming the standard for assessing tornado damage. In Britain, there is a scale similar to the original F-scale but with more divisions for more info, go to the TORRO scale website. In both original F - and TORRO-scales, the wind speeds are based on calculations of the Beaufort wind scale and have never been scientifically verified in real tornadoes. Enhanced F-scale winds are derived from engineering guidelines but still are only judgmental estimates. Because: Nobody knows the true wind speeds at ground level in most tornadoes, and The amount of wind needed to do similar-looking damage can vary greatly, even from block to block or building to building, damage rating is (at best) an exercise in educated guessing. Even experienced damage-survey meteorologists and wind engineers can and often do disagree among themselves on a tornados strength. BACK UP TO THE TOP Who surveys tornado damage Whats the criteria for the National Weather Service to do a survey This varies from place to place and there are no rigid criteria. The responsibility for damage survey decisions at each NWS office usually falls on the Warning-Coordination Meteorologist (WCM) andor the Meteorologist in Charge (MIC). Budget constraints keep every tornado path from having a direct ground survey by NWS personnel so spotter, chaser and news accounts may be used to rate relatively weak, remote or brief tornadoes. Killer tornadoes, those striking densely populated areas, or those generating reports of exceptional damage are given highest priority for ground surveys. Most ground surveys involve the WCM andor forecasters not having shift responsibility the day of the survey. For outbreaks and unusually destructive events--usually only a few times a year--the NWS may support involvement by highly experienced damage survey experts and wind engineers from elsewhere in the country. Aerial surveys are expensive and usually reserved for tornado events with multiple casualties andor massive degrees of damage. Sometimes, local NWS offices may have a cooperative agreement with local media or police to use their helicopters during surveys. BACK UP TO THE TOP Why survey tornado damage How does seeing a bunch of busted trees and houses help with understanding tornadoes Tornadoes still are far from completely understood. Even today, very detailed damage surveys can give us new insights into how tornado winds behave--not only on their own, but in their effects on all kinds of building materials and ecosystems. Building a record of these impacts helps us to understand where the most intense tornado risks are and how tornadoes can cause damage. The benefits of this extend into many areas, including: improving building codes for resistance against most tornadoes (since most tornadoes are weak anyway), the insurance and re-insurance industries, construction designs and practices, and comparisons of tornado damage with their weather situations and radar signatures (for improved watches and warnings). Determining how much of the increased cost and amount of tornado damage is due to larger developed areas (sprawl) and how much is due to shifts in tornado patterns helps for both climate studies and insurance-risk planning. Early studies on the occurrence of strong to violent tornadoes influenced wind-resistance designs of nuclear power plants. BACK UP TO THE TOP How can a tornado destroy one house and leave the next one almost unscratched Most of the time, this happens either with multiple-vortex tornadoes or very small, intense single-vortex tornadoes. The winds in most of a multivortex tornado may only be strong enough to do minor damage to a particular house. But one of the smaller embedded subvortices, perhaps only a few dozen feet across, may strike the house next door with winds over 200 mph, causing complete destruction. Also, there can be great differences in construction from one building to the next, so that even in the same wind speed, one may be flattened while the other is barely nicked. For example, a flimsy, unanchored mobile home may be obliterated while all surrounding objects suffer little or no damage. BACK UP TO THE TOP Ive heard about tornadoes picking up objects and carrying them for miles. Does this happen Yes, numerous tornadoes have lofted (mainly light) debris many miles into the sky, which was then blown by middle - and upper-atmospheric winds for long distances. The vertical winds in tornadoes can be strong enough to temporarily levitate even heavy objects if they have a large face to the wind or flat sides (like roofs, walls, trees and cars), and are strong enough to carry lightweight objects tens of thousands of feet high. Though the heaviest objects, such as railroad cars, can only be airborne for short distances, stories of checks and other papers found over 100 miles away are often true. Numerous checks, papers and other lightweight objects fell from the skies of Missouri, Illinois, Indiana and even Ohio (which the tornado didnt reach) after the Tri-State event of 18 March 1925. The Worcester MA tornado of 9 June 1953 carried mattress pieces high into the thunderstorm, where they were coated in ice, before they fell into Boston Harbor. Pilots reported seeing debris fluttering through the air at high altitude near the thunderstorm which spawned the Ruskin Heights MO tornado of 20 May 1957. Today, airborne plumes of tornado debris sometimes can be detected by Doppler radars in the National Weather Service network. BACK UP TO THE TOP How does the damage from tornadoes compare to that of hurricanes The differences are in scale. Even though winds from the strongest tornadoes far exceed that from the strongest hurricanes, hurricanes typically cause much more damage individually and over a season, and over far bigger areas. Economically, tornadoes cause about a tenth as much damage per year, on average, as hurricanes. Hurricanes tend to cause much more overall destruction than tornadoes because of their much larger size, longer duration and their greater variety of ways to damage property. The destructive core in hurricanes can be tens of miles across, last many hours and damage structures through storm surge and rainfall-caused flooding, as well as from wind. Tornadoes, in contrast, tend to be a few hundred yards in diameter, last for minutes and primarily cause damage from their extreme winds. Where can I find free pictures of tornado damage We have some public domain images of typical examples of F0 through F5 tornado damage linked from this FAQs F-scale page. Otherwise, public-domain tornado damage pictures are scattered among the tornado-related historic news items of various National Weather Service websites. Because web addresses change so often, we dont maintain a listing of them here but you can start your search at this map of all NWS websites. Browse around for damage survey photos in severe weather and tornado event sections of local NWS office pages and please make sure the photos are not copyrighted before using them . If there are any doubts, or to get permission to use copyrighted material, e-mail the webmaster at that office. If you want hardcopies for research projects, the best bet is to download and print public-domain images from a high-quality color printer. Even when using public-domain images, you should give proper credit to the source. Historical archives at local and college libraries might have public-domain hardcopy prints of historical tornado damage in your area. BACK UP TO THE TOP What should I do in case of a tornado That depends on where you are. This list of tornado safety tips covers most situations. BACK UP TO THE TOP What is a tornado watch A tornado watch defines a cluster of counties where tornadoes and other kinds of severe weather are possible in the next several hours. It does not mean tornadoes are imminent, just that you need to be alert, and to be prepared to go to safe shelter if tornadoes do happen or a warning is issued. This is the time to turn on local TV or radio, turn on and set the alarm switch on your weather radio, make sure you have ready access to safe shelter, and make your friends and family aware of the potential for tornadoes in the area. The Storm Prediction Center issues tornado and severe thunderstorm watches here is an example. For more information on tornado watches and other SPC bulletins, go here. BACK UP TO THE TOP What is a tornado warning A tornado warning means that a tornado has been spotted, or that Doppler radar indicates a thunderstorm circulation which can spawn a tornado. When a tornado warning is issued for your town or county, take immediate safety precautions. local NWS offices issue tornado warnings. BACK UP TO THE TOP Do mobile homes attract tornadoes Of course not. It may seem that way, considering most tornado deaths occur in them, and that some of the most graphic reports of tornado damage come from mobile home communities. The reason for this is that mobile homes are, in general, much easier for a tornado to damage and destroy than well-built houses and office buildings. A brief, relatively weak tornado which may have gone undetected in the wilderness, or misclassified as severe straight-line thunderstorm winds while doing minor damage to sturdy houses, can blow a mobile home apart. Historically, mobile home parks have been reliable indicators . not attractors, of tornadoes. BACK UP TO THE TOP Long ago, I was told to open windows to equalize pressure. Now I have heard thats a bad thing to do. Which is right Opening the windows is absolutely useless, a waste of precious time, and can be very dangerous. Tun Sie es nicht. You may be injured by flying glass trying to do it. And if the tornado hits your home, it will blast the windows open anyway. BACK UP TO THE TOP Ive seen a video of people running under a bridge to ride out a tornado. Is that safe Absolutely not Stopping under a bridge to take shelter from a tornado is a very dangerous idea, for several reasons: Deadly flying debris can still be blasted into the spaces between bridge and grade, and impaled in any people hiding there. Even when strongly gripping the girders (if they exist), people may be blown loose, out from under the bridge and into the open--possibly well up into the tornado itself. Chances for survival are not good if that happens. The bridge itself may fail, peeling apart and creating large flying objects, or even collapsing down onto people underneath. The structural integrity of many bridges in tornado winds is unknown--even for those which may look sturdy. Whether or not the tornado hits, parking on traffic lanes is illegal and dangerous to yourself and others. It creates a potentially deadly hazard for others, who may plow into your vehicle at full highway speeds in the rain, hail, andor dust. Also, it can trap people in the storms path against their will, or block emergency vehicles from saving lives. The people in that infamous video were extremely fortunate not to have been hurt or killed. They were actually not inside the tornado vortex itself. but instead in a surface inflow jet --a small belt of intense wind flowing into the base of the tornado a few dozen yards to their south. Even then, flying debris could have caused serious injury or death. More recently, on 3 May 1999. two people were killed and several others injured outdoors in Newcastle and Moore OK, when a violent tornado blew them out from under bridges on I-44 and I-35. Another person was killed that night in his truck, which was parked under a bridge. For more information, meteorologist Dan Miller of NWS Duluth has assembled an online slide presentation about this problem. BACK UP TO THE TOP So if Im in a car. which is supposed to be very unsafe, and shouldnt get under a bridge, what can I do Vehicles are notorious as death traps in tornadoes, because they are easily tossed and destroyed. Either leave the vehicle for sturdy shelter or drive out of the tornados path. When the traffic is jammed or the tornado is bearing down on you at close range, your only option may be to park safely off the traffic lanes, get out and find a sturdy building for shelter, if possible. If not, lie flat in a low spot, as far from the road as possible (to avoid flying vehicles ). However, in open country, the best option is to escape if the tornado is far away. If the traffic allows, and the tornado is distant . you probably have time to drive out of its path. Watch the tornado closely for a few seconds compared to a fixed object in the foreground (such as a tree, pole, or other landmark). If it appears to be moving to your right or left, it is not moving toward you. Still, you should escape at right angles to its track: to your right if it is moving to your left, and vice versa--just to put more distance between you and its path. If the tornado appears to stay in the same place, growing larger or getting closer--but not moving either right or left--it is headed right at you. You must take shelter away from the car or get out of its way fast If the tornado starts to hit your car, get as low as you can while staying in your seatbelt, leaning down and away from the windows and windshield as far as possible. BACK UP TO THE TOP I have a basement, and my friend said to go to the southwest corner in a tornado. Is that good Not necessarily. The SW corner is no safer than any other part of the basement, because walls, floors and furniture can collapse (or be blown) into any corner. The safe southwest corner is an old myth based on the belief that, since tornadoes usually come from the SW, debris will preferentially fall into the NE side of the basement. There are several problems with this concept, including: Tornadoes are mostly circular, so the damaging wind may blow from any direction and Tornadoes themselves may arrive from any direction. In a basement, the safest place is under a sturdy workbench, mattress or other such protection--and out from under heavy furniture or appliances resting on top of the floor above. BACK UP TO THE TOP What is a safe room So-called safe rooms are reinforced small rooms built in the interior of a home, fortified by concrete andor steel to offer extra protection against tornadoes, hurricanes and other severe windstorms. They can be built in a basement, or if no basement is available, on the ground floor. In existing homes, interior bathrooms or closets can be fortified into safe rooms also. FEMA has more details online. Those who have safe rooms, or any other kind of tornado shelter, should register them with the local fire department to help with rescue in case the entrance(s) are blocked by debris. BACK UP TO THE TOP How can building codes help, or hurt, tornado safety Building codes vary greatly across the country, not only from state to state but even from place to place in one county. Codes also have changed over time so that different ages of housing stock in the same community can have different legal standards of strength. Enforcement of codes also can be highly variable, both over time and from place to place. Even the strictest codes wont help without rigorous enforcement. The bottom line: if you buy an existing house or business structure, you cannot fully know its tornado resistance without knocking holes in wall paneling and exposing areas such as wall-foundation attachments, wall-roof connections and (for multi-story structures) internal attachments from one level to another. The best bet for existing stock may be to retrofit or add on a tornado shelter of some sort, depending on your needs and finances. For new construction, the most tornado-ready codes require, among other things: anchor bolts with nuts and washers attached (connecting foundation to floor plate), strong ties (a. k.a. hurricane clips) connecting floor plate to wall studs and wall studs to roof, and use of straight nails or screws for other connections, not cut nails . If you are considering new construction, please check with your local building-regulation agency, demand above-code work to the level you can afford, and directly monitor your builders subcontractors at those crucial early stages to ensure compliance with your own higher standards. NIST has recommended raising standards nationwide, based on their study of the Joplin tornado from 2011. BACK UP TO THE TOP What about community tornado shelters Community tornado shelters are excellent ideas for apartment complexes, schools. mobile home parks, factories, office complexes and other facilities where large groups of people live, work or study. FEMA has some excellent design and construction guidance for these kinds of shelters and a licensed engineer can help customize them to the needs of your facility. BACK UP TO THE TOP What about tornado safety in sports stadiums or outdoor festivals Excellent question--and a very, very disturbing one to many meteorologists and event planners. Tornadoes have passed close to such gatherings on a few occasions, including a horse race in Omaha on 6 May 1975 and a crowded dog track in West Memphis AR on 14 December 1987. A supercell without a tornado hit a riverside festival in Ft. Worth in 1995, catching over 10,000 people outdoors and bashing many of them with hail bigger than baseballs. Tornadoes have hit the football stadium for the NFL Tennessee Titans, and the basketball arena for the NBA Utah Jazz. Fortunately, they were both nearly empty of people at the time. There is the potential for massive death tolls if a stadium or fairground is hit by a tornado during a concert, festival or sporting event, even with a warning in effect. Fans may never know about the warning and even if they do, mass disorder could result in casualties even if the tornado doesnt hit. Stadium, race track and festival managers should work with local emergency management officials to develop a plan for tornado emergencies--both for crowd safety during the watch and warning stages, and (similar to a terrorism plan) for dealing with mass casualties after the tornado. BACK UP TO THE TOP I am a school administrator, and I dont know where to start with developing a safety plan. Can you help Gladly. Every school is different, so a safety plan which works fine for one may not be well-suited for another. There is a website with preparedness tips for school administrators which can provide helpful tips in devising a safety plan. These strategies can be adapted for nursing homes, dorms, barracks and similar structures as well. BACK UP TO THE TOP I am seeking advice to protect employees in a large, one-story commercial building that has pre-poured cement outer walls and a metal roof. We have no basement, the interior offices are drywall partitions with a dropped ceiling and there does not appear to be any area that is secure. The local fire department has no suggestions. This manner of construction is very common however, its hard to know the integrity of any particular building without an engineering analysis, preferably by hiring a specialist with experience in wind engineering. My experience doing damage surveys is that large-span, pre-fab, concrete and metal beam buildings are sturdy up to a failure point--which can vary a lot from site to site--but then crumple quickly and violently once that threshold is reached. A concrete-lined (and - topped) safe room with no windows is recommended. This is an emergency bunker that may double as a restroom, break room or employee lounge, but should be big enough to fit all occupants in the event of a warning. For more information on safe rooms, see FEMAs safe room page. which deals mainly with residential construction, but which can be adapted for office use. FEMA also has posted a page on in-hospital shelter in Kansas, that may be useful for this purpose also. The Wind Engineering Research Center at Texas Tech University also provides guidance about shelters. The insulated concrete form (ICF) is a very wind - and debris-resistant construction method for many small buildings or additions, whether doing new construction or retrofitting. BACK UP TO THE TOP What would happen if a large, violent tornado hit a major city today This has happened on several occasions, including in parts of Oklahoma City on 3 May 1999 and Birmingham on 27 April 2011. Because of excellent, timely watches and warnings and intense media coverage of the Oklahoma tornado long before it hit, only 36 people were killed. The damage toll exceeded 1 billion. Still, it did not strike downtown. and passed over many miles of undeveloped land. Moving the same path north or south in the same area may have led to much greater death and damage tolls. The threat exists for a far worse disaster Placing the same tornado outbreak in the Dallas-Ft. Worth Metroplex. especially during rush hour gridlock (with up to 62,000 vehicles stuck in the path), the damage could triple what was done in Oklahoma. There could be staggering death tolls in the hundreds or thousands, devastated infrastructure, overwhelmed emergency services, and massive amounts of rubble requiring months of cleanup. Ponder the prospect of such a tornados path in downtown Dallas. beispielsweise. The North Texas Council of Governments and NWS Ft. Worth has compiled a very detailed study of several such violent tornado disaster scenarios in the Metroplex, which could be adapted to other major metro areas as well. BACK UP TO THE TOP Could we have some sort of alert system where a computer automatically calls people in a tornado warning to let them know they could be in danger This idea has some merit. Right now, though, there are several logistical problems. First, a tornado may take out phone lines, or the power to run them. Barring that, the phone network reaches saturation pretty easily if someone (or something) tries to try to dial thousands of numbers at once. Finally, people would need to be patient and willing to accept a majority of false alarm calls. Most tornado warnings do not contain tornadoes, because of the uncertainties built into tornado detection which we cant yet help. And even when a tornado happens, it usually hits only a tiny fraction of the warned area (again, because of forecasting uncertainties) so most people called by the automated system would not be directly hit. BACK UP TO THE TOP Are there smartphone apps that offer warnings for tornadoes and other kinds of dangerous weather Yes, private companies have developed several apps that relay NWS tornado warnings to smartphones, based on their location andor user-specified places. For example, you can set some apps to always provide warnings for certain ZIP codes or addresses of interest away from your current location, such as those of your home, business, or friends and loved ones. We cannot endorse any particular apps, but a search in your device providers app store should yield some that are highly rated, along with reviews by users. NOAA has partnered with major cellular providers to push Wireless Emergency Alerts to most modern cell phones, and those include tornado warnings. Also, some local governments have enacted warning-alert systems that alarm phones in their jurisdictions when warnings are issued. Please check with your local emergency management agency to see if such a system is in place in your area, or soon will be. Caution: cell-phone warnings cannot work if the phone system is disabled, and might fail or be delayed if the network is overloaded (as can happen during a major storm or other disaster). BACK UP TO THE TOP I recently moved from the Plains and noticed that there are no tornado warning sirens here. Is this because tornadoes dont occur here Isnt it required to have sirens everywhere There is no nationwide requirement for tornado sirens. Siren policy is local and varies from place to place. The National Weather Service has no control over sirens or siren policy . The NWS issues watches and warnings but it is up to the local governments to have a community readiness system in place for their citizens. In conversations with emergency managers and spotter coordinators, I have found that the two most common reasons for a lack of sirens are low budgets and the misconception that tornadoes cannot happen in an area. Your city andor county emergency manager would be the first person to query about the tornado preparedness program in your community. Remember: outdoor sirens are for outdoor use . Everyone should have ways to receive warnings besides sirens. BACK UP TO THE TOP Our office would like to print signs (universal symbol image type signs) similar to emergency exit, fire extinguisher, etc. that could be used to identify designated tornado shelter areas. Can you provide me with a graphic or something I can use Sure There isnt a universal tornado shelter symbol yet. Any such sign should be very bold and noticeable--yet designed to be simple, with minimal visual clutter, so even a small child can recognize it. In response to this question, here is one possible tornado shelter sign which may be printed and used freely. There are also versions with arrows pointing right. left. up. and down. The signs ideally should be printed in color, on heavy card stock or sticker paper for durability. BACK UP TO THE TOP What were the deadliest U. S. tornadoes The Tri-state tornado of 18 March 1925 killed 695 people as it raced along at 60-73 mph in a 219 mile long track across parts of Missouri, Illinois and Indiana, producing F5 damage. The death toll is an estimate based on the work of Grazulis (1993) older references have different counts. This event also holds the known record for most tornado fatalities in a single city or town: at least 234 at Murphysboro IL. The deadliest of the modern era (since 1950) was on 22 May 2011, when a large EF5 tornado crossed Joplin, MO, causing 158 direct fatalities. The 25 deadliest tornadoes on record are listed here. We also have web links related to this and other major tornado events. BACK UP TO THE TOP What were the deadliest U. S. tornado days What are the time limits of a tornado day anyway In the modern era (1950 onward), the outbreak of 27 April 2011 (12Z-12Z) set a record with about 316 people killed (preliminary calendar-day total. subject to further revision). Behind that, on 3 April 1974 (12Z-12Z), the main day of the two-day Super Outbreak, tornadoes killed 310 people. We have two lists of the top 15 deadliest tornado days since 1950, one from midnight to midnight CST (by calendar day, Central Standard Time), then from 12Z to 12Z (the convective day for SPC outlooks). Because some tornado outbreaks persist well into the night and following morning, one can slice and dice the time sampling in many ways, and come up with different numbers. These are the two most common measures of a day that SPC has used, historically. BACK UP TO THE TOP What was the biggest outbreak of tornadoes As with the previous question, that depends on how you measure or bracket an outbreak. SPC typically uses the 24-hour convective day starting and ending at 12 UTC (7 a. m. CDT). Using that cut-off, the greatest swarm of tornadoes was 175 on 27-28 April 2011, with a damage-rating breakdown of EF0: 59, EF1: 65, EF2: 20, EF3: 16, EF4: 11, and EF5: 4. This supplanted the Super Outbreak of 147 known U. S. tornadoes on 3-4 April, 1974. The 1974 outbreak still holds the record for the most F5 tornadoes in a single day, with seven. Only one other 24-hour outbreak yielded over 100 confirmed tornadoes--Hurricane Beulah in 1967 (115). Hurricane Ivan of 2004 produced 118 tornadoes in three days, but in separate, daily cycles. By calendar day . 27 April 2011 also holds the modern record with 209 tornadoes confirmed so far, with a damage scale breakdown of EF0: 62, EF1: 78, EF2: 33, EF3: 21, EF4: 11, and EF5: 4. BACK UP TO THE TOP What was the biggest known tornado On 31 May 2013, a deadly, multiple-vortex tornado near El Reno, OK carved an official maximum path width of 2.6 miles, based on damage and some radar estimates. That width barely exceeded the Hallam, Nebraska F4 tornado of 22 May 2004. Mobile-radar-based research accepted to the Bulletin of the AMS indicates the width of the 30 ms (67 mph) winds in the El Reno circulation was much bigger--at least 7 km (4.3 miles). Measuring the width of a tornado can be as messy and unclear as defining a tornado. El Reno and Hallam probably were close to the maximum size for tornadoes but it is quite possible that others this size or somewhat larger have occurred that werent sampled by high-resolution radars or surveyed so carefully in the field. BACK UP TO THE TOP What single month had the most tornadoes The record for most tornadoes in any month (since modern tornado record keeping began in 1950) was set in April 2011, when SPC data show 817 tornadoes. BACK UP TO THE TOP What was the strongest tornado What is the highest wind speed in a tornado Nobody knows. Tornado wind speeds have only been directly recorded in the weaker ones, because strong and violent tornadoes destroy weather instruments. Mobile Doppler radars such as the OU Doppler on Wheels have remotely sensed tornado wind speeds above ground level as high as about 302 mph (on 3 May 1999 near Bridge Creek OK)--the highest winds ever found very near Earths surface by any means. In addition to having what we now would consider EF5-class winds, that tornado caused actual F5 damage . But the greatest ground-level wind speeds in the most violent tornadoes never have been directly measured. BACK UP TO THE TOP What was the costliest tornado The costliest tornado on record was the EF5 in Joplin, MO on 22 May 2011, with estimated 2.8 billion in damage (2011 dollars). The Tuscaloosa (AL) tornado of 27 April 2011 was the previous record holder, at 2,450,000,000 (2011 dollars). Recent forensic work by Harold Brooks of NSSL has established that the Storm Data entry for a Georgia tornado in 1973, which had been listed here, had a large multiplication error. As a result, that event is no longer ranked. A top-10 damage listing is online here. BACK UP TO THE TOP Do you have a list of EF5 and F5 tornadoes Yes, and here it is. Remember: Because the only way we can compare all tornadoes is by whatever damage they caused, and EF5F5 damage is only possible when tornadoes hit well-built structures, the true violence of most historical tornadoes is unknown--especially before the middle to late 20th century. BACK UP TO THE TOP Where can I find information on violent tornado outbreaks Many individual sites, including local NWS office web pages. contain historic links to events in their jurisdictions. The SPC hosts a large website devoted exclusively to historic violent tornado events. with path plots, meteorological graphics and history links. BACK UP TO THE TOP Where can I find stories and descriptions of historic tornadoes Web links change constantly, so its difficult to find and maintain an updated listing. It helps when searching online or microfilm newspaper records to know the date and location of the tornado(es). On the Internet, a search engine can help you find information of varying quality on tornado events. Try different combinations of keywords like Oak Lawn tornado and Illinois tornadoes, for example, if searching for online material on a tornado in Oak Lawn IL. We also have compiled a PowerPoint poster depicting some noteworthy North American tornado outbreaks. A genealogy-oriented site, GenDisasters. may be helpful for that perspective. Your local librarys historical archives also might contain a great deal of insight onto effects of past tornadoes in that area. For places away from your home area, use the Internet search engines or write or e-mail local and university libraries in the area the tornado(es) occurred. Many larger city and university libraries have a copy of the out-of-print book Significant Tornadoes, 1680-1991 by Thomas P. Grazulis--an excellent source for stories about thousands of tornadoes in U. S. history. Toms online site at The Tornado Project also has some historical tornado descriptions, though far fewer than the book. BACK UP TO THE TOP What tornadoes have killed people this year Last year or other years SPC keeps online maps and tables of killer tornadoes for recent years here. Most of this years information is preliminary and may change when the final storm summaries are sent to the National Centers for Environmental Information (NCEI. formerly NCDC) by local National Weather Service offices. Information for all tornadoes and severe weather events--including killer tornadoes--is provided by month (and organized by state) in the NCEI publication Storm Data . BACK UP TO THE TOP Will historical tornadoes be assigned Enhanced F-scale ratings Probably not. To get a consistent climatology, records and descriptions of tens of thousands of tornadoes would have to be examined one by one, and there are neither plans nor money nor staffing at any tornado-related office for such a gigantic task. However, it certainly is possible that individual tornadoes or outbreaks may be examined for Enhanced F-scale rating from time to time, as interested researchers decide to revisit specific events of historic significance. Tornadoes from February 2007 onward will be rated using the Enhanced F-scale and can be compared to each other in that way. BACK UP TO THE TOP Have there been instances of ships or boats being capsized or badly damaged by tornadoes (waterspouts) Yes. Watercraft are especially dangerous in tornadoes because of the open and unprotected exposure, difficulty of reaching safe shelter and direct risk of drowning. On 1 Jul 1814, a tornado moved off land into Charleston SC harbor, hitting the anchored schooner Alligator . The Gator sank and killed 25 of 40 crew. This is the deadliest marine-tornado event in U. S. records. On 17 Jun 1978, the tour boat Whippoorwill . on Pomona Lake KS, was capsized by a tornado. killing 16. BACK UP TO THE TOP Has a tornado hit the SPC Not directly, thankfully The closest call was on 10 May 2010. when the earliest stages of the east NormanLittle Axe tornados ground circulation developed a few hundred yards south of the National Weather Center building that now houses SPC. Observers here gazed almost directly upward at the funnel. Other tornadoes could be seen from our previous facility on 3 May 1999 and 4 October 1998. the latter at night, both in the distance in Moore. Small debris from the 24 May 2011 Goldsby, OK tornado fell on the National Weather Center grounds, and a few people there saw final stages of that tornado through rain and hail. The 10 May 2010 tornado also passed very close to the 5-cm wavelength, dual-polarization OU-PRIME research radar, which captured impressive, high-resolution data (PDF conference paper ). BACK UP TO THE TOP NOTE: Historical tornado information used here comes from both the SPC database and Grazulis (1993). TORNADO CLIMATOLOGY and DATA How many tornadoes hit the US yearly Recent trends indicate around 1200, give or take a few hundred per year. The actual average is unknown, because tornado spotting and reporting methods have changed so much in the last several decades that the officially recorded tornado climatologies are believed to be incomplete. Also, in the course of recording thousands of tornadoes, errors are bound to occur. Events can be missed or misclassified and some non-damaging tornadoes in remote areas could still be unreported. BACK UP TO THE TOP Have there been any major changes or trends in yearly tornado counts Tornado reports have increased, especially around the installation of the NEXRAD Doppler radar system in the mid 1990s. This doesnt mean that actual tornado occurrence has gone up, however. The increase in tornado numbers is almost entirely in weak (EF0-EF1) events that are being reported far more often today due to a combination of better detection, greater media coverage, aggressive warning verification efforts, storm spotting, storm chasing, more developmental sprawl (damage targets), more people, and better documentation with cameras (including cell phones) than ever. Modern averages of roughly 1200 per year nationwide probably are as close to the truth as weve ever seen. Another few decades of well-documented tornadoes will tell us more. To compare tornado counts before Doppler radars, we have to either adjust historical trends statistically to account for the unreported weak tornadoes of before, or look only at strong to violent (EF2-EF5) tornadoes, whose records are much better documented and more stable. When we do that, very little overall change has occurred since the 1950s. Here is a graph of raw and adjusted trends through 2015. About the only thing we can infer with good certainty from this is that the year-to-year variability seems to be swinging more wildly up and down since 2000, even though the averages are essentially staying flat. The physical cause of those larger up-and-down swings is not known yet. BACK UP TO THE TOP How many tornadoes have there been in the US this year and how does it compare to previous years Killer tornadoes Such tornado report totals are in an online table of monthly tornado statistics at the SPC. Remember, those are preliminary numbers which may be amended at any time. BACK UP TO THE TOP How many people are killed every year by tornadoes How do most deaths happen in tornadoes On average, tornadoes kill about 60 people per year--most from flying or falling (crushing) debris. The actual number of tornado deaths in a year can vary wildly -- from single digits to hundreds, depending on many factors from both weather and society. BACK UP TO THE TOP What was the deadliest tornado year in the modern era SPC defines the modern era of tornado recordkeeping as 1950-present, the time frame of its database. As of this writing, the record year since 1950 is 2011, when tornadoes killed 550 people in 15 states. Follow this link for the latest map and listing of those events. Before 1950, several years had nearly similar or higher tornado death tolls but the exact numbers are uncertain due to more archaic communications, more people missing and unaccounted for, unknown numbers of unreported deaths, and then-customary exclusion of certain groups from death tolls in some older events. The year 1925--including the Tri-State Tornado--had the greatest toll with 794 known tornado deaths. BACK UP TO THE TOP What is tornado season Tornado season usually means the peak period for historical tornado reports in an area, when averaged over the history of reports. There is a general northward shift in tornado season in the U. S. from late winter through mid summer. The peak period for tornadoes in the southern plains, for example, is during May into early June. On the Gulf coast, it is earlier during the spring in the northern plains and upper Midwest, it is June or July. Remember: tornadoes can happen any time of year if the conditions are right If you want to know the tornado peak periods for your area, Harold Brooks of NSSL has prepared numerous tornado probability graphics. which include distribution during the year. BACK UP TO THE TOP How early in the year do tornadoes start happening Tornadoes can happen any day or night of the year. Indeed, the earliest on modern record (since 1950) was two minutes into the new year--12:02 a. m. CST, 1 January 2011, in Attala County, MS. The average first-tornado date in the U. S. was January 11, for the entire 1950-2011 time frame. The latest first-tornado was on 15 February 2003, in Marengo County, AL, meaning that the nation had 45 days of tornado-free weather to start that year. BACK UP TO THE TOP What is Tornado Alley Tornado Alley is a nickname in the popular media for a broad swath of relatively high tornado occurrence in the central U. S. Various Tornado Alley maps which you may see can look different because tornado occurrence can be measured many ways--by all tornadoes, tornado county-segments, strong and violent tornadoes only, and databases with different time periods. Most recently, Concannon, et al.. have prepared a Tornado Alley map using significant tornado data. Remember, this is only a map of greatest incidence. Violent or killer tornadoes do happen outside this Tornado Alley every year. Tornadoes can occur almost anywhere in the U. S. including west of the Rockies and east of the Appalachians, and even in Canada and overseas. BACK UP TO THE TOP Does global warming cause tornadoes No. Thunderstorms do. The harder question may be, How will climate change influence tornado occurrence The best answer is: We dont know. According to the National Science and Technology Councils Scientific Assessment on Climate Change . Trends in other extreme weather events that occur at small spatial scales--such as tornadoes, hail. lightning. and dust storms--cannot be determined at the present time due to insufficient evidence. This is because tornadoes are short-fused weather . on the time scale of seconds and minutes, and a space scale of fractions of a mile across. In contrast, climate trends take many years, decades, or millennia, spanning vast areas of the globe. The numerous unknowns dwell in the vast gap between those time and space scales. Climate models cannot resolve tornadoes or individual thunderstorms. They can indicate broad-scale shifts in three of the four favorable ingredients for severe thunderstorms (moisture, instability and wind shear), but as any severe weather forecaster can attest, having some favorable factors in place doesnt guarantee tornadoes. Our physical understanding indicates mixed signals--some ingredients may increase (instability), while others may decrease (shear), in a warmer world. The other key ingredient (storm-scale lift), and to varying extents moisture, instability and shear, depend mostly on day-to-day patterns, and often, even minute-to-minute local weather. Finally, tornado recordkeeping itself also has been prone to many errors and uncertainties, doesnt exist for most of the world, and even in the U. S. only covers several decades in detailed form. BACK UP TO THE TOP Does El Nino cause tornadoes No. Neither does La Nina. Both are major changes in sea surface temperature in the tropical Pacific which occur over the span of months. U. S. tornadoes happen thousands of miles away on the order of seconds and minutes. El Nino does adjust large-scale weather patterns. But between that large scale and tornadoes, there are way too many variables to say conclusively what role El Nino (or La Nina) has in changing tornado risk and it certainly does not directly cause tornadoes. A few studies have shown some loose associations between La Nina years and regional trends in tornado numbers from year to year but that still doesnt prove cause and effect. Weak associations by year or season may be as close as the ENSO-to-tornado connection can get--because there are so many things on the scales of states, counties and individual thunderstorms which can affect tornado formation. For more detailed information, see The Relationship between El Nino, La Nina and United States Tornado Activity. a research paper by Schaefer and Tatom, or this paper by Cook and Schaefer on wintertime tornadoes and the ENSO cycle. BACK UP TO THE TOP What city has been hit by the most tornadoes Oklahoma City. The exact count varies because city limits and tornado reporting practices have changed over the years but the known total is now over 100. The Norman NWS has prepared a detailed listing of OKC-area tornadoes. Another way to measure tornado count and avoid the vagaries of political boundaries is to use tornado hits within a radius though this method will include tornadoes in some nearby communities. BACK UP TO THE TOP I noticed the word preliminary used a lot in the SPC tornado stats, and final too. What do those mean Tornado data usually reaches SPC first from local storm reports (LSRs), warnings or other bulletins sent by local NWS forecast offices. Such reports are usually sent within the first day or two after a severe weather event, before all the information on a tornado is known. In fact, some tornado information might not be known for many weeks or months--for example, if someone who was injured dies from his injuries a long time afterward. That is why we call all tornado data preliminary until the National Centers for Environmental Information publication Storm Data is completed. Storm Data contains the final information on all severe weather events, except for the whole-tornado path combining that is done at SPC. BACK UP TO THE TOP How many tornadoes have there been in my state or county The actual number is unknown, because it is likely that (throughout the course of history) many tornadoes were either not reported or erroneously categorized. Recorded tornadoes nationwide are listed and described in the National Centers for Environmental Information publication Storm Data . and listed in CSV (comma-separated value) files at the SPCs WCM website. NCEI has developed an interactive online severe weather database which you can use to search your state andor county for tornado segments and other severe weather reports. Jeff Evans has broken down the SPC tornado data into table of tornadoes by state for three decades ending in 2009. NOTE: NCEI tornado data is not for whole tornadoes, but for county-segments and there are still some incorrect county codings or other errors as documented by Doug Speheger of NWS Norman. BACK UP TO THE TOP Where can I obtain SPC tornado data A variety of tornado data and plots, including several decades worth of tornado records in CSV (comma-separated value) files, is freely available for all on the SPC Warning-Coordination Meteorologists page. The SPC data files are in CSV format and called ONETOR because they represent whole-tornado paths instead of county segments. CSV is a plain-text (ASCII) format readable by most major data-analysis software. The decoding legend for SPC ONETOR data columns is offered in PDF format. We also offer a GIS-compatible form of SPC severe weather data (including tornadoes). BACK UP TO THE TOP How does tornado data get to SPC The SPC doesnt produce the tornado data. Local NWS offices collect records of tornadoes and other severe weather for their county-warning areas, then send it on a monthly basis to the NWS Performance Branch in Washington, DC. From there, the data go to the National Centers for Environmental Information (formerly NCDC), then to SPC. At SPC, we combine county-border-crossing segments from NCEI into whole-tornado paths by about March of each year, then upload the previous years files to the WCM page for free download and use by anybody in the world. BACK UP TO THE TOP Where else can I obtain climatological tornado data Besides the NCEI online lookup. an increasing number of local NWS offices have posted tornado stats and event descriptions for their warning jurisdictions. Reminder . NCEI and most local data are broken down by county path segments and not whole tornadoes. State-by-state value-added data can also be obtained from the Tornado Project databases. BACK UP TO THE TOP What are county-segments in NCEI tornado data A county-segment is that portion of a tornados path within a single county. If a tornado stays in one county, then a tornado is the same as a segment. But this also means that tornadoes are counted twice when they cross into another county, three times when they enter a third county, and so forth. The reason for county-segment tornado recordkeeping is that the National Weather Service historically has verified tornado warnings by county. So when you look at NCEI tornado database (also reflected in Storm Data or the NWS Natural Hazard Statistics (based on Storm Data ), you are not counting tornadoes, but instead county-segments of tornado tracks . This inflates the tornado totals often reported by media and others who do not notice this important distinction. BACK UP TO THE TOP Is there a listing or data set for tropical cyclone tornadoes Yes. A data set in MS Excel format is maintained at SPC (links to Excel file and readme. txt documentation). The data is updated yearly and may change as new or corrected information arrives. For an explanation of the tropical cyclone tornado data, the background and how it is compiled, please see this paper. BACK UP TO THE TOP Why do ratings from the original F-scale differ between SPC and others tornado records Both original F-scale and the Enhanced F-scale are based on a subjective judgment of damage intensity, but the EF-scale has very specific guidelines for rating an assortment of damage targets. By contrast, the F-scale only specified well-built homes with all else left to guesswork. Consistency was a major problem as well, because hundreds of people rated tornadoes for Storm Data during the F-scale era. Currently and in recent decades, damage ratings for the official database are made by meteorologists at each local forecast office where tornadoes are reported. Sometimes, first-hand damage surveys are done, but because of travel-budget constraints, ratings often must be made from spotter, chaser andor media accounts. In order to assign F-scales to tornadoes from before about 1978 (the year varies from state to state), NSSFC contracted with college students to cross-reference the NSSFC file with newspaper articles. When information that conflicted with Storm Data were uncovered, a judgment call was made as to what most likely occurred and if necessary, the NSSFC information was corrected in the final data base. Also, several new tornadoes (previously unreported ones) were uncovered and added to the record. There were enough of these changes that the NSSFC (now SPC) database sometimes has differences with Storm Data . even before accounting for the county segments of paths done at NCEI. Tom Grazulis (1993) sometimes changed the official tornado ratings for Tornado Project records based on his judgment of damage from historical tornado accounts in newspapers and photographs. So, with all this interpretation going on, it is easy to see how tornado records have become inconsistent for many events. BACK UP TO THE TOP Do countries other than the US get tornadoes How many How strong We know that tornadoes have been documented from many other nations, but we dont have a solid record of their frequency or damage potential in most areas. Several European countries, including the United Kingdom, Romania and Finland, have begun keeping detailed tornado records in recent years, as does Canada. A consortium of European weather researchers has compiled the European Severe Weather Database. which includes tornadoes. Tornado records even in those nations are not compiled the same way as those in the U. S. and cant be compared directly. Indeed, in most of the world, there is no systematic documentation of tornadoes, other than those that happen to cause great damage and death, or that are caught by chance on someones camera. To judge where else tornadoes are most common, we have to use a mix of actual tornado reports with heavy statistical analysis of weather records that indicate conditions favorable for them. Such a blend of recorded and inferential study indicates that the U. S. remains tops in tornado production, with secondary tornado-prone areas including the Canadian Prairie Provinces, Bangladesh, Britain, northeastern Mexico, northern Argentina and southern Brazil, and portions of southern Russia. The Mexican maximum (northern Coahuila, east of the Serranias del Burro range ) and Canadian tornado prone zones each are border-crossing extensions of U. S. conditions. BACK UP TO THE TOP Do we know of other F5 or EF5 rated tornadoes besides those in the U. S. Canada had its first recorded F5 tornado on 22 June 2007 near Elie, MB (documentation from Environment Canada ). Canada had not yet adopted the Enhanced Fujita Scale. BACK UP TO THE TOP There is an old legend that my town is protected from tornadoes by the (hill, river, spirit, etc.). Is there any truth to this No. Many towns which have not suffered a tornado strike contain well-meaning people who perpetuate these myths but there is no basis for them besides the happenstance lack of a tornado. Many other towns used to have such myths before they were hit, including extreme examples like Topeka KS (F5 damage, 16 killed, 1966) and Waco TX (F5 damage, 114 killed, 1953). Violent tornadoes have crossed rivers of all shapes and sizes. The deadliest tornado in US history (Tri-state Tornado of 18 March 1925, F5 damage, 695 killed) roared undeterred across the Mississippi River, as have numerous other violent tornadoes. Almost every major river east of the Rockies has been crossed by a significant tornado. Tornadoes have crossed high elevations in the Appalachians, Rockies and Sierra Nevada also. The Salt Lake City tornado of 11 August 1999 crossed a canyon--descending one side and rising up the other about halfway along its path. In 1987, a violent tornado (rated F4 by Fujita) crossed the Continental Divide in Yellowstone National Park. BACK UP TO THE TOP What is the highest-elevation tornado Do they happen in the mountain West The highest elevation a tornado has ever occurred is unknown but it is at least 10,000 feet above sea level. On 7 July 2004, a hiker observed and photographed a tornado at 12,000 feet in Sequoia National Park, California. That probably was the highest elevation tornado observed in the U. S. On 28 July 2012, a spectacular tornado moved across ground elevations of around 11,900 feet, along the flank of Mt. Evans, CO. On 21 July 1987, there was a violent (F4 damage) tornado in Wyoming between 8,500 and 10,000 feet in elevation, the highest altitude ever recorded for a violent tornado. There was F3 damage from a tornado at up to 10,800 ft elevation in the Uinta Mountains of Utah on 11 August 1993. While not so lofty in elevation, the Salt Lake City tornado of 11 August 1999 produced F2 damage. On August 31, 2000, a supercell spawned a photogenic tornado in Nevada. Tornadoes are generally a lot less frequent west of the Rockies per unit area with a couple of exceptions. One exception is the Los Angeles Basin, where weak-tornado frequency over tens of square miles is on par with that in the Great Plains. Elsewhere, there are probably more high-elevation Western tornadoes occurring than we have known about, just because many areas are so sparsely populated, and they lack the density of spotters and storm chasers as in the Plains. BACK UP TO THE TOP Why does it seem like tornadoes avoid downtowns of major cities Simply. downtowns cover tiny land areas relative to the entire nation. The chance of any particular tornado hitting a major downtown is quite low--not for any meteorological reason, but simply because downtowns are small targets. Even when tornadoes hit metro areas their odds of hitting downtown are small out of space considerations alone. For example, downtown Dallas (inside the freeway loop) covers roughly three square miles--Dallas County, about 900 square miles. For a brief tornado in Dallas County, its odds of hitting downtown are only about 1 in 300. Still, downtown tornadoes have happened. including at least four hits on St. Louis alone. The idea of large buildings destroying or preventing a tornado is pure myth. Even the largest skyscrapers pale in size and volume when compared to the total circulation of a big tornado from ground through thunderhead. BACK UP TO THE TOP Whats the risk of another super-outbreak like April 3-4, 1974 Its rare but we dont know how rare, because an outbreak like that arguably has only happened once since any tornado records have been kept. The outbreak of 27 April 2011 is the only other roughly comparable event in the era of modern records, 1950-present. There is no way to know if the odds of such events are one in every 50 years, 10 years or 1,000 years, since we just do not have the long climatology of reasonably accurate tornado numbers to use. So the bigger the outbreaks, the less we can reliably judge their potential to recur. BACK UP TO THE TOP What are the chances of a tornado near my house The frequency that a tornado can hit any particular square mile of land is about every thousand years on average, but varies around the country. The reason this is not an exact number is because we dont have a long and accurate enough record of tornadoes to make more certain (statistically sound) calculations. The probability of any tornado hitting within sight of a spot (lets say 25 nautical miles) also varies during the year and across the country. For maps of tornado-hazard risk, we offer two reliable sources: Weekly national tornado probabilities from SPC Threat maps and animations by Harold Brooks (NSSL). BACK UP TO THE TOP What was the first tornado climatology John P. Finley, in the 1880s, was the first person to intensively study U. S. tornadoes and their patterns of occurrence. His pioneering volume Tornadoes (1887) discussed his effort-intensive compilation of tornado records, as well as many (now outmoded) safety and meteorological notions about tornadoes. The History of Science department at the University of Oklahoma has a full scan of this book online. BACK UP TO THE TOP NOTE: Tornado climatology information used here may come from either the SPC database or Grazulis (1993). SPOTTING AND CHASING How do I become a storm spotter Local National Weather Service offices offer spotter training sessions each year. Contact the Warning Coordination Meteorologist at the office which serves you for info on when and where they conduct these sessions, and how to become a spotter for them. There is also a national spotters organization, SKYWARN. which can help you learn about storm spotting and get you in contact with spotting experts. It also helps to have a historical perspective on the storm spotting program. BACK UP TO THE TOP Whats the difference between a spotter and a chaser The differences are in method and motivation. Chasers are more mobile than spotters, and unlike most spotters, travel hundreds of miles and across state lines to observe storms. Spotters primary function is to report critical weather information, on a live basis, to the National Weather Service through some kind of local spotter coordinator. Chasers, on the other hand, may be doing it for any number of reasons, including scientific field programs, storm photography, self-education, commercial video opportunity, or news media coverage. Some storm spotters also do occasional chasing outside their home area and some chasers are certified and equipped to do real-time spotting. BACK UP TO THE TOP How do I learn more about storm chasing How do I become a tornado chaser The term tornado chasing is not very accurate since tornadoes are such a small fraction of the storm chasing experience. Storm chasing can be very dangerous and is not something to be taken frivolously. The National Weather Service does not endorse storm chasing because of the risk, but welcomes storm reports from those who do chase. One way to learn more about storm chasing is to is to become a storm spotter in your local area, learning about the character of storms while contributing to public safety through the warning process. After gaining experience observing storms as a spotter, you can then decide if chasing is for you. BACK UP TO THE TOP Who were the first storm chasers The late Roger Jensen is believed to be the first person who actively hunted for severe thunderstorms and tornadoes - in the upper Midwest in the late 1940s. David Hoadley of Falls Church, VA, has been doing so annually since 1956, and is widely considered the pioneer storm chaser. The late Neil Ward of NSSL was the first storm-chasing scientist, using insights gained from his field observations of tornadoes to build more complex and accurate tornado simulations in his laboratory. The first federally funded, scientific storm intercept teams fanned out from NSSL across the Oklahoma plains in 1972 but their greatest early success came a year later with their intensive documentation of the Union City, OK, tornado of 24 May 1973. This was also the first time a tornado was measured intensively by both storm intercept teams and Doppler radar --the forerunning event to the nationwide network of Doppler radars now used for early warning. BACK UP TO THE TOP Are there films or videos I can get which tell the real story of storm chasers Hundreds of storm chasing videos and several TV documentaries have been made, most since the mid-1990s. Unfortunately, most of them available online or in stores and catalogs (even from educational outlets) are very misleading--featuring non-stop tornadoes or heavily emphasizing thrillseeking and danger. They typically have little or no mention of safety, forecasting skill, learning, extensive down time and the long days and weeks of travel which often yield no tornadoes. Storm-chasing videos can be found via many related web sites, and typically featureonly cuts from the most exciting few moments of long trips. Video producer Blake Naftel is in the process of compiling a historical documentary on storm chasing. BACK UP TO THE TOP I saw a low-hanging cloud in a thunderstorm. Was it a tornado Without being there or seeing good video of it, I cant say. Many low-hanging clouds are not tornadoes, but sometimes are wrongly reported as tornadoes anyway. The most important things to look for when you see a suspicious cloud feature are: Rapid cloud-base rotation, if you are close enough to make out cloud movement, and A concentrated, whirling debris or dust cloud at ground level under the thunderstorm base. Imagine this spinning rapidly. It is common to have one without the other. Many thunderstorms produce dust plumes in their outflow these tend to move in one direction and not rotate. In gustnadoes. there is spinning motion at ground level but not at cloud base (therefore, not a tornado). If the ground is wet enough, or the circulation weak enough, there may not be any debris under a rotating cloud base. But persistent rotation in the cloud base is potentially very dangerous and should be reported. At night, also look for persistent cloud lowering to ground, especially if accompanied by a power flash. BACK UP TO THE TOP Whats the difference between a funnel cloud and a tornado What is a funnel cloud In a tornado, a damaging circulation is on the ground-- whether or not the cloud is . The phrase, tornado on the ground, is redundant A tornado, by definition, is on the ground. A true funnel cloud rotates, but has no ground contact or debris, and is not doing damage. If it is a low-hanging cloud with no rotation. it is not a funnel cloud. Vorsicht . tornadoes can happen without a funnel and what looks like only a funnel cloud may be doing damage which cant be seen from a distance. Some funnels are high-based and may never reach the surface. Still, since a funnel cloud might quickly become a tornado (remember rotation), it should be reported by spotters. BACK UP TO THE TOP Why are some tornadoes white. and others black or gray or even red Tornadoes tend to look darkest when looking southwest through northwest in the afternoon. In those cases, they are often silhouetted in front of a light source, such as brighter skies west of the thunderstorm. If there is heavy precipitation behind the tornado, it may be dark gray, blue or even white, depending on where most of the daylight is coming from. This happens often when the spotter is looking north or east at a tornado, and part of the forward-flank andor rear-flank cores. Tornadoes wrapped in rain may exhibit varieties of gray shades on gray. if they are visible at all. Lower parts of tornadoes also can assume the color of the dust and debris they are generating for example, a tornado passing across dry fields in western or central Oklahoma may take on the hue of the red soil so prevalent there. BACK UP TO THE TOP What is a gustnado A gustnado is a small and usually weak whirlwind which forms as an eddy in thunderstorm outflows. They do not connect with any cloud-base rotation and are not tornadoes. But because gustnadoes often have a spinning dust cloud at ground level, they are sometimes wrongly reported as tornadoes. Gustnadoes can do minor damage (e. g. break windows and tree limbs, overturn trash cans and toss lawn furniture), and should be avoided. BACK UP TO THE TOP What is a wedge tornado A rope tornado These are slang terms often used by storm observers to describe tornado shape and appearance. Remember, the size or shape of a tornado does not say anything certain about its strength Wedge tornadoes simply appear to be at least as wide as they are tall (from ground to ambient cloud base). Rope tornadoes are very narrow, often sinuous or snake-like in form. Tornadoes often (but not always) assume the rope shape in their last stage of life and the cloud rope may even break up into segments. Again, tornado shape and size does not signal strength Some rope tornadoes can still do violent damage of EF4 or EF5. BACK UP TO THE TOP What is a satellite tornado Is it a kind of multivortex tornado No. There are important distinctions between satellite and multiple-vortex tornadoes. A satellite tornado develops independently from the primary tornado, not inside it as with a subvortex. The tornadoes are separate and distinct as the satellite tornado orbits its much larger companion within the same mesocyclone. Their cause is unknown but they seem to form most often in the vicinity of exceptionally large and intense main tornadoes. This paper (PDF) offers more documentation and examples of satellite tornadoes. BACK UP TO THE TOP What is a landspout This is storm-chaser slang for a non-supercell tornado. So-called landspouts resemble waterspouts in that way, and also in their typically small size and weakness compared to the most intense supercell-spawned tornadoes. But landspouts are tornadoes by definition and they are capable of doing significant damage and killing people. BACK UP TO THE TOP Who does scientific tornado research The National Severe Storms Laboratory has been the major force in tornado-related research for several decades. NSSL has been a leader in Doppler radar development, research and testing, and has run numerous field programs to study tornadoes and other severe weather since the early 1970s. Others heavily involved with tornado research include UCARNCAR. the University of Oklahoma. the Tornado Project. Tornado History Project. and overseas, the European Severe Storms Lab (Germany) and TORRO (UK). Members of the SELSSPC staff have done research related to forecasting tornadoes for many years. Almost every university with an atmospheric science program, as well as many local National Weather Service offices, have also published some tornado-related studies. BACK UP TO THE TOP Who are, or have been, some of the major tornado researchers The list of important contributors to tornado science is so long that it cant be put here without unjustly leaving someone out. Most of the big names in tornado research are found often in the accompanying list of scientific references. The biggest name, however, is probably the late T. Theodore Ted Fujita of the University of Chicago. Although his meteorological interests and publications covered numerous topics, he concentrated on aspects of tornado research, including damage (yielding the F-scale ), vortex structure, photogrammetry. risk assessment, tornado climatology, and mesoscale analysis for forecasting tornado occurrence. For more information on Ted Fujita, there are tributes and biographies online. as well as a list of his publications. BACK UP TO THE TOP What is the history of tornado research As with the history of tornado prediction. the story of tornado research is a very rich dossier that cant be told well enough in this limited space to do it justice. NSSL offers a quick overview of their considerable tornado-research involvement in an online timeline. For more in-depth histories, please see this formal article by Chuck Doswell and an informal converence paper by Howie Bluestein. The references cited in those papers lead down interesting, branching trails of historical discovery. BACK UP TO THE TOP Has there ever been anything done like Dorothy in the movie Twister . What was TOTO In Twister . Dorothy was a large, reinforced metal bin containing small instrument pods which, with help from refabricated soda cans, were supposed to be drawn into a tornado when the tornado would crack Dorothy open. The idea for Dorothy was taken from a real device which OU and NSSL weather scientists used in the early-mid 1980s called TOTO --the TOtable Tornado Observatory. Both Dorothy and TOTO now are on display at the National Weather Center in Norman. BACK UP TO THE TOP What happened with those researchers who were killed by an Oklahoma tornado in 2013 Engineer Tim Samaras, his son Paul, and meteorologist Carl Young died in the 31 May 2013 El Reno tornado when an extremely intense subvortex, buried within the larger, rain-wrapped circulation, looped northwestward toward their vehicle and blew it off the road. Theirs were the first storm-researcher fatalities in the field. Tim, Paul and Carl were highly respected within the severe-storms community, and their loss stunned all who knew them. Here is the NOAA statement on this tragic event. National Geographic offers a web page with video and links summarizing Tims work. The Denver Post also has posted an in-depth feature on the story. BACK UP TO THE TOP What are turtles Turtles are small, squat, heavy, aerodynamic instrument packages which were designed to withstand tornado wind speeds while measuring temperature, pressure and humidity at ground level. During the VORTEX program, they were sometimes placed on the ground at 100-250 yard intervals in the path of tornadic mesocyclones. Scientists are still analyzing data from those deployments. Turtles do not measure winds. More recent models have been deployed in a few strong to violent tornadoes with promising results. BACK UP TO THE TOP What was Project VORTEX That was the acronym for V erification of the O rigin of R otation in T ornadoes EX periment, conducted in the springs of 1994 and 1995 in the southern and central U. S. plains, and led by Erik Rasmussen of NSSL. The basic idea was to gather the most dense possible set of observations in tornadic supercells. from sensors in cars, planes, balloons, turtles (small instrument packages which could be placed on the ground), and portable radars. The main goal is to better understand the cause of tornado formation in thunderstorms. Subsequent, smaller field measurement programs were conducted under the name SubVORTEX. For more details on VORTEX, go to the online VORTEX storybook page. Was there another VORTEX Yes. A group of atmospheric scientists (many also involved with the original project) prepared a major follow-up, VORTEX-2, for May and June 2009-2010. Thanks to a quiet and uncooperative atmosphere for tornadoes, the 2009 project phase only sampled one, near LaGrange, WY (5 June 2009). but it was the most intensively observed tornado in history at the time. The 2010 version sampled several supercells and a few weak tornadoes. BACK UP TO THE TOP What is VORTEX-SE VORTEX-SE is a southeastern U. S. follow-up to the earlier, similarly named Plains states projects VORTEX and VORTEX2. The basic physics of the atmosphere (and the four ingredients needed for supercells -- moisture, instability, lift and vertical shear) dont change across the globe. However, the balance and source of the ingredients often differs in the Southeast compared to the Great Plains, where most field projects regarding tornadoes have occurred. Because of the greater vegetation and rougher terrain in the Southeast, VORTEX2 (slated at least for March-April 2016 and probably 2017) will involve more static platforms to measure the atmosphere around storms as they go by. VORTEX 2, according to the website. is a research program to understand how environmental factors characteristic of the Southeastern U. S. affect the formation, intensity, structure, and path of tornadoes in this region. VORTEX-SE will also determine the best methods for communicating forecast uncertainty of these events to the public, and evaluate public response. As such, it also will study social-science and communications aspects of Southeastern tornado situations, which is a first for a field project devoted to storms. BACK UP TO THE TOP What is photogrammetry Tornado photogrammetry is the use of film or video to determine the speed of movement of some kind of tracer: usually a large piece of debris or a persistent cloud element. From these, the wind speed can be inferred with varying and sometimes unknown reliability. Photogrammetric analyses of tornadoes used to be much more common in the 1970s and 1980s than today. Now, portable Doppler radars like the DOW are the main tools used in the effort to determine the strength of tornado winds. Major difficulties with photogrammetry of tornadoes include: Only the component of motion across the field of view can be measured Usually, only debris in the outer part of the tornado can be tracked, because of dust and cloud material cloaking any objects farther in, causing a failure to sample many of the theoretically stronger winds and Debris large enough to film from a safe distance, and to track across many movie or video frames, may be moving much slower than the wind carrying it. Still, photogrammetry has been an insightful and interesting tool in determining tornado vortex characteristics and very generalized wind estimates. BACK UP TO THE TOP Have tornadoes been simulated in laboratories If so, when and how The late Neil Ward of NSSL began building smoke vortex chambers in his home in the late 1950s, which led to a tornado simulation laboratory at NSSL in the 1960s and early 1970s. Among other concepts, Ward simulated the evolution of a single, primary tornado vortex into multiple vortices, which was not well-documented in the real atmosphere until films of multivortex tornadoes began appearing in the middle to late 1970s. Subsequent tornado simulators were constructed for Ted Fujita of the University of Chicago, and at Purdue University. The Purdue tornado simulator was much larger and operated such that air flow velocity and pressure could be measured in the vortices. Nowadays, tornado chambers may be built in the home for fun and study. BACK UP TO THE TOP What are the DOWs (Dopplers on Wheels) The DOWs are portable Doppler radars securely mounted on flatbed trucks, and operated in the field by intercept teams from the Doppler on Wheels project. DOWs have measured fine-scale details of tornado features, including eyes and inflow jets, along with wind speeds a short distance above the ground. The strongest wind speed determined from DOW data was about 302 mph--about 30 meters above ground level--in the Bridge CreekMoore, Oklahoma, tornado of 3 May 1999. Please keep in mind that radar-indicated winds cant be compared well to anemometer winds. This is because of the difference in height above ground, and because the radar winds are scanned in the instant of a beam (instead of sampled over several seconds, as with anemometers). BACK UP TO THE TOP Are any other mobile radars in use in tornado research Several mobile radars now ply the Plains yearly in serch of tornadoes to scan. The NOAA X-POL (NOXP) is a dual-polarized X-Band unit. The Advanced Radar Research Center at OU runs a Rapid-scan X-band Polarimetric Radar (RaXpol ), also dual-polarized in the X band, as well as the Atmospheric Imaging Radar (AIR). A mobile phased-array radar, MWR-05XP. also has been deployed for tornado interrogation. A flatbed-mounted Doppler radar called SMART-R (Shared Mobile Atmosphere Research and Teaching Radar) has been developed at Texas AM University, with help from OU, NSSL and Texas Tech. More information is online at Texas AM. Though its first goal is to sample details of the wind fields in landfalling hurricanes, it can be used in the vicinity of supercells and tornadoes also. As with the DOWs. onboard computers display and store the data from these units. Mobile-radar data aided in the rating of the EF5 El Reno-Piedmont, OK tornado (24 May 2011), and helped to document a rare tornado merger with that event. Some private chase teams and tours have marine radars mounted on their vehicles however, these are for promotional purposes and have no use in research. Marine-radar signals actually tend to interfere with research units like those named above. BACK UP TO THE TOP I am studying tornadoes in-depth. What are some technical scientific references I can use Here is a sampling of technical scientific references for those doing in-depth research studies. They are found in peer-reviewed journals and conference preprints of the American Meteorological Society. and also in university publications. It is only a partial list many other articles can be found by looking in the reference sections of these papers. These references can contain very technical terminology and mathematical equations, and are written mainly for meteorologists, meteorology students and educated laypersons who are familiar with scientific journals in meteorology. BACK UP TO THE TOP INDEX OF TOPICS To find places in the Online Tornado FAQ where these subjects were mentioned, just click on the numbers following each. Note that numbers are not necessarily in chronological order. The main reference to a topic is given first. To return to the Index after clicking on a number, hit the BACK button on your browser.
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