Explosive cyclogenesis

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The Braer Storm of January 1993 explosively deepened to a record low of 914 mbar (hPa)

Explosive cyclogenesis (also referred to as a weather bomb,[1][2][3] meteorological bomb,[4] explosive development,[1] bomb cyclone[5][6] or bombogenesis[7][8][9]) is the rapid deepening of an 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 24 mbar (hPa) or more in 24 hours.[10][11]

This is a predominantly maritime, winter event,[10] but also occurs in continental settings.[12][13] This process is the extratropical equivalent of the tropical rapid deepening.

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.[5]

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 in the Monthly Weather Review.[5][10] In 1980, Sanders and his colleague John Gyakum defined a "bomb" as an extratropical cyclone that deepens by at least (24 sin φ/ sin 60°)mb in 24 hours, where φ represents latitude in degrees. This is based on the definition, standardised by Bergeron, for explosive development of a cyclone at 60°N as deepening by 24mb in 24 hours.[14] 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".[10][12]

Formation

Baroclinic instability has been cited as one of the principal mechanisms for the development of most explosively deepening cyclones.[15] 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.[16] 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.[17]

Regions and motion

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.[18]

In the Northern Hemisphere the maximum frequency of explosively deepening cyclones is found within or to the north of the Atlantic Gulf Stream and Kuroshio Current in the western Pacific,[10] and 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.[19]

Explosively deepening cyclones south of 50°S often show equator-ward movement, in contrast with the poleward motion of most Northern Hemisphere bombs.[17] 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.[17]

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.[20][21] This use of "bomb" may lead to confusion with the more strictly defined meteorological term. In Japan, the term 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.[22][23]

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'?".[24]

Further reading

References

  1. ^ a b "Fierce 'weather bomb' batters Britain". The Telegraph. 9 December 2011. Retrieved 21 March 2013. 
  2. ^ "The worst storm in years?". Met Office Blog. 28 January 2013. Retrieved 21 March 2013. 
  3. ^ Edwards, Tim (9 December 2011). "Scotland storm: what is a weather bomb?". The Week. London, United Kingdom: Dennis Publishing. Retrieved 4 April 2013. 
  4. ^ O'Hanlon, Larry (25 February 2013). "Look out -- 'meteorological bomb' is on the way!". NBC News. Retrieved 21 March 2013. 
  5. ^ a b c Williams, Jack (20 May 2005). "Bomb cyclones ravage northwestern Atlantic". USA Today. Retrieved 22 March 2013. 
  6. ^ Feltman, Rachel (3 January 2018). "What the heck is a bomb cyclone?". Popular Science. Retrieved 6 January 2018. 
  7. ^ "Ryan explains Bomb Cyclogenesis". WBRZ News 2 Louisiana. Archived from the original on 12 April 2013. Retrieved 21 March 2013. 
  8. ^ Freedman, Andrew (1 March 2013). "Meteorological bomb explodes over New England". Washington Post. Retrieved 21 March 2013. 
  9. ^ Rodman, Kristen (23 January 2014). "What is Bombogenesis?". Accuweather. Retrieved 31 January 2014. 
  10. ^ a b c d e Sanders, Frederick; Gyakum, John R (1980). "Synoptic-Dynamic Climatology of the 'Bomb'". Monthly Weather Review. 108 (10): 1589–606. Bibcode:1980MWRv..108.1589S. doi:10.1175/1520-0493(1980)108<1589:SDCOT>2.0.CO;2. 
  11. ^ Chelsea Harvey (November 10, 2014). "Here's What Caused The 'Bomb Cyclone' That's About To Freeze The Northern US". Business Insider. Retrieved October 8, 2017. 
  12. ^ a b "The Bomb". blog.ametsoc.org. 27 October 2010. Retrieved 21 March 2013. [self-published source?]
  13. ^ MacDonald, Bruce C; Reiter, Elmar R (1988). "Explosive Cyclogenesis over the Eastern United States". Monthly Weather Review. 116 (8): 1568–86. Bibcode:1988MWRv..116.1568M. doi:10.1175/1520-0493(1988)116<1568:ECOTEU>2.0.CO;2. 
  14. ^ Baker, Laura (2011). Sting Jets in Extratropical Cyclones (Ph.D.). University of Reading. 
  15. ^ WENG, H. Y.; BARCILON, A. (1987). "Favorable environments for explosive cyclogenesis in a modified two-layer Eady model". Tellus A. 39A (3): 202–214. Bibcode:1987TellA..39..202W. doi:10.1111/j.1600-0870.1987.tb00301.x. 
  16. ^ Fink, Andreas H.; Pohle, Susan; Pinto, Joaquim G.; Knippertz, Peter (2012). "Diagnosing the influence of diabatic processes on the explosive deepening of extratropical cyclones" (PDF). Geophysical Research Letters. 39 (7): n/a–n/a. Bibcode:2012GeoRL..39.7803F. doi:10.1029/2012GL051025. Retrieved 2 June 2013. 
  17. ^ a b c Lim, Eun-Pa; Simmonds, Ian (2002). "Explosive Cyclone Development in the Southern Hemisphere and a Comparison with Northern Hemisphere Events" (PDF). Monthly Weather Review. 130 (9): 2188–2209. Bibcode:2002MWRv..130.2188L. doi:10.1175/1520-0493(2002)130<2188:ECDITS>2.0.CO;2. Archived from the original (PDF) on 19 April 2013. Retrieved 21 March 2013. 
  18. ^ Black, Mitchell Timothy; Pezza, Alexandre Bernardes (2013). "A universal, broad-environment energy conversion signature of explosive cyclones". Geophysical Research Letters. 40 (2): 452–7. Bibcode:2013GeoRL..40..452B. doi:10.1002/grl.50114. 
  19. ^ Yoshiike, Satoki; Kawamura, Ryuichi (2009). "Influence of wintertime large-scale circulation on the explosively developing cyclones over the western North Pacific and their downstream effects" (PDF). Journal of Geophysical Research. 114 (D13). Bibcode:2009JGRD..11413110Y. doi:10.1029/2009JD011820. Archived from the original (PDF) on 6 February 2011. Retrieved 9 April 2013. 
  20. ^ Kreft, Peter (4 March 2012). "The Bomb". Metservice NZ blog. Archived from the original on 17 September 2012. Retrieved 21 March 2013. 
  21. ^ "New Zealand's media doesn't understand what a "Weather Bomb" is". WeatherWatch.co.nz. 27 March 2017. Retrieved 27 March 2017. 
  22. ^ 爆弾低気圧とは . Bomb Cyclones Information Database (in Japanese). Kyushu University. Retrieved 2 September 2014. 
  23. ^ Milner, Rebecca (3 December 2012). "Japan's top 10 buzzwords for 2012". Japan Pulse Blog, The Japan Times. Retrieved 25 April 2013. 
  24. ^ "Meet the Canadian who helped coin the term 'weather bomb'". CBC News. 5 January 2018. Retrieved 5 January 2018. 

External links

  • BBC Weather, What is a weather 'bomb'?
  • Bomb Cyclone Data of the Northwest Pacific Ocean (in Japanese)
  • Lorenz Energy Cycle - Linking Weather and Climate (MET 6155)
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