View source for Explosive cyclogenesis

{{short description|Rapidly deepening extratropical cyclonic low-pressure area}}
{{About|extratropical cyclones|tropical cyclones|Rapid intensification}}
[[File:BraerStorm1993.png|250px|thumbnail|right|The [[Braer Storm|Braer Storm of January 1993]] explosively deepened to a record low of 913 mbar (hPa)]]

'''Explosive cyclogenesis''' (also referred to as a '''weather bomb''',<ref name="09Dec2011" >{{cite news |title=Fierce 'weather bomb' batters Britain |url=https://www.telegraph.co.uk/topics/weather/8945152/Fierce-weather-bomb-batters-Britain.html |archive-url=https://web.archive.org/web/20111209225827/http://www.telegraph.co.uk/topics/weather/8945152/Fierce-weather-bomb-batters-Britain.html |url-status=dead |archive-date=9 December 2011 |access-date=21 March 2013 |newspaper=The Telegraph|date=9 December 2011}}</ref><ref>{{cite news |title=The worst storm in years?|url=http://metofficenews.wordpress.com/tag/weather-bomb/|access-date=21 March 2013|newspaper=Met Office Blog |date=28 January 2013}}</ref><ref name=deepening>{{cite news |url=http://www.theweek.co.uk/health-science/weather/43448/scotland-storm-what-weather-bomb |title= Weather bomb: the storm phenomenon brewing over Britain |first=Tim|last=Edwards |date=10 December 2014|access-date=21 November 2024|work=[[The Week]] |publisher=[[Dennis Publishing]]|location=London, United Kingdom}}</ref> '''meteorological bomb''',<ref>{{cite news|last=O'Hanlon|first=Larry|title=Look out -- 'meteorological bomb' is on the way!|url=http://science.nbcnews.com/_news/2013/02/25/17088963-look-out-meteorological-bomb-is-on-the-way?lite|access-date=21 March 2013|newspaper=NBC News |date=25 February 2013}}</ref> '''explosive development''',<ref name="09Dec2011" /> '''bomb cyclone''',<ref name="Williams" >{{cite news |last=Williams |first=Jack|title=Bomb cyclones ravage northwestern Atlantic |url=http://usatoday30.usatoday.com/weather/tg/wnoreast/wbombs.htm|access-date=22 March 2013|newspaper=USA Today |date=20 May 2005}}</ref><ref>{{cite news| url=https://www.popsci.com/bomb-cyclone| title=What the heck is a bomb cyclone?| newspaper=Popular Science| last=Feltman| first=Rachel| date=3 January 2018| access-date=6 January 2018}}</ref> or '''bombogenesis'''<ref>{{cite web|title=Ryan explains Bomb Cyclogenesis|url=http://www.wbrz.com/videos/ryan-explains-bomb-cyclogenesis/|publisher=WBRZ News 2 Louisiana|access-date=21 March 2013|url-status=dead|archive-url=https://archive.today/20130412034719/http://www.wbrz.com/videos/ryan-explains-bomb-cyclogenesis/|archive-date=12 April 2013}}</ref><ref>{{cite news |last=Freedman |first=Andrew |title=Meteorological bomb explodes over New England|url=http://voices.washingtonpost.com/capitalweathergang/2010/03/meteorological_bomb_explodes_o.html|archive-url=https://web.archive.org/web/20131224103707/http://voices.washingtonpost.com/capitalweathergang/2010/03/meteorological_bomb_explodes_o.html|url-status=dead|archive-date=December 24, 2013|access-date=21 March 2013|newspaper=Washington Post|date=1 March 2013}}</ref><ref>{{cite news|last=Rodman|first=Kristen|title=What is Bombogenesis?|url=http://www.accuweather.com/en/weather-news/what-is-bombogenesis/22365706|access-date=31 January 2014|newspaper=Accuweather|date=23 January 2014}}</ref>) is the rapid deepening of an [[Extratropical cyclone|extratropical cyclonic]] [[low-pressure area]]. The change in pressure needed to classify something as explosive cyclogenesis is [[latitude]] dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by {{convert|24|mb|inHg}} or more in 24 hours.<ref name="SandersGyakum" >{{cite journal |doi=10.1175/1520-0493(1980)108<1589:SDCOT>2.0.CO;2 |year=1980 |volume=108 |issue=10 |pages=1589–606 |title=Synoptic-Dynamic Climatology of the 'Bomb' |journal=Monthly Weather Review |last1=Sanders |first1=Frederick |last2=Gyakum |first2=John R |bibcode=1980MWRv..108.1589S |doi-access=free }}</ref><ref name="bomb cyclone">{{cite web|url=http://www.businessinsider.com/what-is-a-bomb-cyclone-weather-system-2014-11|title=Here's What Caused The 'Bomb Cyclone' That's About To Freeze The Northern US|author=Chelsea Harvey|publisher=Business Insider|date=November 10, 2014|access-date=October 8, 2017}}</ref> This is a predominantly maritime, winter event,<ref name="SandersGyakum" /><ref name="AMS_Glossary_20120220"/> but also occurs in continental settings.<ref name="Ametsoc" >{{cite news |title=The Bomb|url=http://blog.ametsoc.org/news/the-bomb/|access-date=21 March 2013|newspaper=blog.ametsoc.org |date=27 October 2010}}</ref><ref>{{cite journal |doi=10.1175/1520-0493(1988)116<1568:ECOTEU>2.0.CO;2 |year=1988 |volume=116 |issue=8 |pages=1568–86 |title=Explosive Cyclogenesis over the Eastern United States |journal=Monthly Weather Review |last1=MacDonald |first1=Bruce C |last2=Reiter |first2=Elmar R |bibcode=1988MWRv..116.1568M |doi-access=free }}</ref> This process is the extratropical equivalent of the tropical [[rapid deepening]]. Although their [[cyclogenesis]] is entirely different from that of tropical cyclones, bomb cyclones can produce winds of {{convert|74|to|95|mph|km/h|round=5|abbr=on}}, the same order as the first categories of the [[Saffir–Simpson scale]], and yield heavy precipitation. Even though only a minority of bomb cyclones become this strong, some weaker ones can also cause significant damage.

==History==
In the 1940s and 1950s, meteorologists at the [[Bergen School of Meteorology]] began informally calling some storms that grew over the sea "bombs" because they developed with a great ferocity rarely seen over land.<ref>{{cite news |last1=Williams |first1=Jack |title=USATODAY.com |url=http://usatoday30.usatoday.com/weather/tg/wnoreast/wbombs.htm |access-date=11 June 2025 |work=usatoday30.usatoday.com |date=2005-05-20 |archive-url=https://web.archive.org/web/20130416023351/http://usatoday30.usatoday.com/weather/tg/wnoreast/wbombs.htm |archive-date=2013-04-16}}</ref>

By the 1970s, the terms "explosive cyclogenesis" and even "meteorological bombs" were being used by [[Massachusetts Institute of Technology|MIT]] professor Fred Sanders (building on work from the 1950s by [[Tor Bergeron]]), who brought the term into common usage in a 1980 article published to the ''[[Monthly Weather Review]]''.<ref name="Williams" /><ref name="SandersGyakum" /> In the article, Sanders and his colleague John Gyakum defined a "bomb" as an [[extratropical cyclone]] that deepens by at least {{math|(24 sin {{var|φ}} / sin 60°)}}&nbsp;mb in 24 hours, where {{mvar|φ}} represents latitude. This is based on the definition, standardised by Bergeron, for explosive development of a cyclone at 60°N as deepening by 24 mb in 24 hours.<ref>{{cite thesis |type=Ph.D. |first=Laura |last=Baker |title=Sting Jets in Extratropical Cyclones |publisher=University of Reading |year=2024}}</ref> Sanders and Gyakum noted that an equivalent intensification is dependent on latitude: at the poles this would be a drop in pressure of 28 mb/24 hours, while at 25 degrees latitude it would be only 12 mb/24 hours. All these rates qualify for what Sanders and Gyakum called "1 bergeron".<ref name="SandersGyakum" /><ref name="Ametsoc" /> Sanders' and Gyakum's 1980 definition, which is used in the [[American Meteorological Society]]'s Glossary of Meteorology, said that the "bomb" was "predominantly" a "maritime, cold season event".<ref name="SandersGyakum"/><ref name="AMS_Glossary_20120220">{{Cite web| title = Bomb |series=Glossary of Meteorology| access-date = 27 December 2023 |date=20 February 2012|work=[[American Meteorological Society]]| url = https://glossary.ametsoc.org/wiki/Bomb}}</ref>

In early 2014 in the North Atlantic, fourteen wind events out of twenty that had reached hurricane-force, underwent bombogenesis, the process that creates a bomb cyclone, according to [[National Oceanic and Atmospheric Administration]] (NOAA).<ref name="NOAA_nd">{{Cite web| work = US Department of Commerce and National Oceanic and Atmospheric Administration | title = What is bombogenesis?| access-date = 27 December 2023 |date=n.d. | url = https://oceanservice.noaa.gov/facts/bombogenesis.html}}</ref> NOAA said that bombogenesis "occurs when a [[Middle latitudes|midlatitude]] cyclone rapidly intensifies, dropping at least 24 [[millibar]]s over 24 hours."<ref name="NOAA_nd"/>

==Formation==
[[Baroclinity|Baroclinic]] instability has been cited as one of the principal mechanisms for the development of most explosively deepening cyclones.<ref>{{cite journal|last1=Weng|first1=H. Y.|last2=Barcilon |first2=A.|title=Favorable environments for explosive cyclogenesis in a modified two-layer Eady model|journal=Tellus A|year=1987|volume=39A|issue=3|pages=202–214|doi=10.1111/j.1600-0870.1987.tb00301.x|bibcode=1987TellA..39..202W}}<!--|access-date=23 March 2013--></ref> However, the relative roles of baroclinic and [[adiabatic process|diabatic]] processes in explosive deepening of extratropical cyclones have been subject to debate (citing case studies) for a long time.<ref name="Fink" >{{cite journal|last1=Fink|first1=Andreas H.|last2=Pohle |first2=Susan |last3=Pinto |first3=Joaquim G. |last4=Knippertz |first4=Peter |title=Diagnosing the influence of diabatic processes on the explosive deepening of extratropical cyclones|journal=Geophysical Research Letters|year=2012|volume=39|issue=7|pages=n/a|doi=10.1029/2012GL051025|url=http://www.geomet.uni-koeln.de/fileadmin/Dokumente/Arbeitsgruppen/Meteorologie/Fink__Andreas/Publikationen/fppk_grl_artikel2012_master_rev060312_finalafterproofs.pdf|access-date=2 June 2013|bibcode = 2012GeoRL..39.7803F |doi-access=free}}</ref> Other factors include the relative position of a 500-hPa trough and [[Hypsometric equation|thickness]] patterns, deep [[Troposphere|tropospheric]] [[frontogenesis|frontogenetic processes]] which happen both upstream and downstream of the surface low, the influence of air–sea interaction, and [[latent heat]] release.<ref name="Lim" />

===Regions and motion===
[[File:Northwest Pacific cyclone 2017-10-24 2350Z.png|thumb|right|Absorbing the remnants of a powerful [[tropical cyclone]] can trigger explosive cyclogenesis]]
The four most active regions where extratropical explosive cyclogenesis occurs in the world are the Northwest [[Pacific]], the North Atlantic, the Southwest Pacific, and the South Atlantic.<ref name="Black" >{{cite journal |doi=10.1002/grl.50114 |title=A universal, broad-environment energy conversion signature of explosive cyclones |journal=Geophysical Research Letters |volume=40 |issue=2 |pages=452–7 |year=2013 |last1=Black |first1=Mitchell Timothy |last2=Pezza |first2=Alexandre Bernardes |bibcode=2013GeoRL..40..452B |doi-access=free }}</ref>

In the [[Northern Hemisphere]] the maximum frequency of explosively deepening cyclones is found within or to the north of the Atlantic [[Gulf Stream]], the [[Kuroshio Current]] in the western Pacific,<ref name="SandersGyakum" /> and in the eastern Pacific. In the [[Southern Hemisphere]] it is found with [[Australian east coast low]]s above the [[East Australian Current]], which shows the importance of air-sea interaction in initiating and rapidly developing extratropical cyclones.<ref>{{cite journal |last1=Yoshiike |first1=Satoki |last2=Kawamura |first2=Ryuichi |title=Influence of wintertime large-scale circulation on the explosively developing cyclones over the western North Pacific and their downstream effects |journal=Journal of Geophysical Research |year=2009 |volume=114 |issue=D13 |doi=10.1029/2009JD011820 |bibcode=2009JGRD..11413110Y |doi-access=free }}</ref>

Explosively deepening cyclones south of 50°S often show equator-ward movement, in contrast with the poleward motion of most Northern Hemisphere bombs.<ref name="Lim">{{cite journal|last1=Lim |first1=Eun-Pa |last2=Simmonds |first2=Ian |title=Explosive Cyclone Development in the Southern Hemisphere and a Comparison with Northern Hemisphere Events |journal=Monthly Weather Review |year=2002 |volume=130 |issue=9 |pages=2188–2209 |doi=10.1175/1520-0493(2002)130<2188:ECDITS>2.0.CO;2 |bibcode=2002MWRv..130.2188L |doi-access=free }}</ref> Over the year, 45 cyclones on average in the Northern Hemisphere and 26 in the Southern Hemisphere develop explosively, mostly in the respective [[Hemispheres of Earth|hemisphere]]'s winter time. Less seasonality has been noticed in bomb cyclogenesis occurrences in the Southern Hemisphere.<ref name="Lim" />

==Other uses of "weather bomb"==
The term "weather bomb" is popularly used in [[New Zealand]] to describe dramatic or destructive weather events. Rarely are the events actual instances of explosive cyclogenesis, as the rapid deepening of low pressure areas is rare around New Zealand.<ref>{{cite news |last=Kreft |first=Peter |title=The Bomb |url=http://blog.metservice.com/2012/03/the-bomb/ |access-date=21 March 2013 |newspaper=Metservice NZ blog |date=4 March 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120917054302/http://blog.metservice.com/2012/03/the-bomb |archive-date=17 September 2012 }}</ref><ref>{{cite news|title=New Zealand's media doesn't understand what a 'Weather Bomb' is|url=http://www.weatherwatch.co.nz/content/new-zealands-media-doesnt-understand-what-a-weather-bomb|access-date=27 March 2017|publisher=WeatherWatch.co.nz|date=27 March 2017|language=en}}</ref> This use of "bomb" may lead to confusion with the more strictly defined meteorological term. In [[Japan]], the term {{nihongo|''bomb cyclone''|爆弾低気圧|bakudan teikiatsu}} is used both academically and commonly to refer to an extratropical cyclone which meets the meteorological "bomb" conditions.<ref>{{cite web |title=Bakudan teikiatsu to wa |script-title=ja:爆弾低気圧とは |url=http://fujin.geo.kyushu-u.ac.jp/meteorol_bomb/about/index.php |website=Bomb Cyclones Information Database |publisher=Kyushu University |access-date=2 September 2014 |language=ja}}</ref><ref>{{cite news |last=Milner |first=Rebecca |title=Japan's top 10 buzzwords for 2012|url=http://blog.japantimes.co.jp/japan-pulse/japans-top-10-buzzwords-for-2012/ |access-date=25 April 2013 |department=Japan Pulse Blog |work=[[The Japan Times]] |date=3 December 2012}}</ref>

The term "bomb" may be somewhat controversial. When European researchers protested that it was a rather warlike term, Fred Sanders, the coauthor of the paper which introduced the meteorological usage quipped: "So why are you using the term 'front'?"<ref>{{cite news|title=Meet the Canadian who helped coin the term 'weather bomb'|url=http://www.cbc.ca/news/technology/canadian-coined-term-weather-bomb-1.4474431|access-date=5 January 2018 |publisher=[[CBC News]] |date=5 January 2018|language=en}}</ref>

==See also==
{{Portal|Weather}}
* [[Cyclogenesis#Extratropical cyclones|Cyclogenesis, extratropical cyclones]] 
* [[Extratropical cyclone#Formation|Extratropical cyclone, formation]]
* [[List of atmospheric pressure records in Europe#Notable non-tropical pressures over the North Atlantic|Notable non-tropical pressures over the North Atlantic]]
* [[Superstorm]]

==References==
{{Reflist|28em}}

==External links==
{{Wiktionary|bombogenesis}}
* [http://www.bbc.co.uk/weather/features/30397614 "What is a weather 'bomb'?"]—[[BBC Weather]]
* [http://fujin.geo.kyushu-u.ac.jp/meteorol_bomb/view/index.php Bomb Cyclone Data] of the Northwest Pacific Ocean {{in lang|ja}}
* [http://linkingweatherandclimate.com/learn/lorenz.php Lorenz Energy Cycle - Linking Weather and Climate (MET 6155)]

{{Cyclones}}

[[Category:Extratropical cyclones]]
[[Category:Synoptic meteorology and weather]]