explosive cyclogenesis

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.{{citation needed|date=March 2025}}

By the 1970s, the terms "explosive cyclogenesis" and even "meteorological bombs" were being used by 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. 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°)}} 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.{{cite thesis |type=Ph.D. |first=Laura |last=Baker |title=Sting Jets in Extratropical Cyclones |publisher=University of Reading |year=2024}} 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". 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".{{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}}

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).{{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}} NOAA said that bombogenesis "occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours."

Baroclinic instability has been cited as one of the principal mechanisms for the development of most explosively deepening cyclones.{{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}} However, the relative roles of baroclinic and diabatic processes in explosive deepening of extratropical cyclones have been subject to debate (citing case studies) for a long time.{{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}} Other factors include the relative position of a 500-hPa trough and thickness patterns, deep tropospheric frontogenetic processes which happen both upstream and downstream of the surface low, the influence of air–sea interaction, and latent heat release.

File:Northwest Pacific cyclone 2017-10-24 2350Z.png 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.{{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 }}

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, and in the eastern Pacific. In the Southern Hemisphere it is found with Australian east coast lows above the East Australian Current, which shows the importance of air-sea interaction in initiating and rapidly developing extratropical cyclones.{{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 }}

Explosively deepening cyclones south of 50°S often show equator-ward movement, in contrast with the poleward motion of most Northern Hemisphere bombs.{{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 }} Over the year, 45 cyclones on average in the Northern Hemisphere and 26 in the Southern Hemisphere develop explosively, mostly in the respective hemisphere's winter time. Less seasonality has been noticed in bomb cyclogenesis occurrences in the Southern Hemisphere.

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.{{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 }}{{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}} 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.{{cite web |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}}{{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}}

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'?"{{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}}

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{{Reflist|28em}}

{{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)]

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Category:Extratropical cyclones

Category:Synoptic meteorology and weather