Explosive cyclogenesis (also known as climate bomb, meteorological bomb, explosive development or bombogenesis) refers strictly to an area of low extratropical cyclonic pressure that deepens rapidly. To enter this category, the central pressure of a depression at 60 ° latitude is required to decrease by 24 mb (hPa) or more in 24 hours.
This is a predominantly maritime, winter event, but it also occurs in continental environments. This process is the extratropical equivalent of rapid tropical deepening.
In the 1940s and 1950s, meteorologists from the Bergen School of Meteorology began to informally call some storms that grew on the “bombs” of the sea because they developed with great ferocity that was rarely seen on earth.
In the 1970s the terms “explosive cyclogenesis” and even “weather bombs” were being used by Professor MIT Fred Sanders (based on the work of the 1950s by Tor Bergeron), who brought the term to common use in a 1980 article in the monthly climate Review. In 1980, Sanders and his colleague John Gyakum defined a “bomb” as an extratropical cyclone that deepens at least (24 sin φ / sin 60˚) mb in 24 hours, where φ represents the latitude in degrees. This is based on the definition, standardized by Bergeron, for the explosive development of a cyclone at 60˚N as depth by 24mb in 24 hours. Sanders and Gyakum observed that an equivalent intensification depends on latitude: at the poles this would be a drop in pressure of 28 mb / 24 hours, while at 25 degrees of latitude it would be only 12 mb / 24 hours. All these rates qualify for what Sanders and Gyakum called “1 bergeron”.
Baroclinic instability has been cited as one of the main mechanisms for the development of cyclones that deepen more explosively. However, the relative roles of baroclinic and diabatic processes in the explosive deepening of extratropical cyclones have been subject to debate (citing case studies) for a long time. Other factors include the relative position of a 500 hPa channel and thickness patterns, deep tropospheric frontogenetic processes that occur both upstream and downstream of the low surface, the influence of air-sea interaction and the release of latent heat.
Regions and movement
The four most active regions where extratropical explosive cyclogenesis occurs in the world are the Pacific Northwest, the North Atlantic, the southwestern Pacific and the South Atlantic.
In the northern hemisphere, the maximum frequency of explosive deepening cyclones is within or north of the Atlantic Gulf Stream and the Kuroshio Current in the western Pacific, and in the southern hemisphere, the Australian East Coast is below the East Australian current. importance of air-sea interaction to initiate and rapidly develop extratropical cyclones.
Cyclones of explosive deepening south of 50˚S often show an equatorial movement, in contrast to the poleward movement of most pumps in the northern hemisphere. During the year, 45 cyclones on average in the Northern Hemisphere and 26 in the Southern Hemisphere develop explosively, mainly in the winter of the respective hemispheres. Less seasonality has been noted in the occurrences of bomb cyclogenesis in the Southern Hemisphere.
Other uses of “weather bomb”
The term “weather bomb” is popularly used in New Zealand to describe dramatic and / or destructive weather phenomena. Very rarely are these cases of explosive cyclogenesis, since rapid deepening of low pressure areas is rare in New Zealand. This use of “bomb” can lead to confusion with the more strictly defined meteorological term.
The term is often misused in North America, confused with heavy snowfall and Norwegian mountains (which sometimes suffer from the rapid drop in pressure required to meet the strict meteorological definition). In Japan, the term cyclone pump (圧 弾 低 気 圧, bakudan teikiatsu) is used both academically and commonly to refer to an extratropical cyclone that meets the weather conditions of the “pump”.