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Bomb cyclone: A blast from the past

Q: Is “bomb cyclone” a new term? I don’t remember seeing it in the past. Who decides when a new weather term will be used?

A: No, “bomb cyclone” isn’t new. Since 1980, scientists have used “bomb” as a meteorological term for a large, rapidly growing cyclone storm system. The related terms “bomb cyclone” and “weather bomb” emerged in the mid-1980s, but only recently made their way into popular journalism.

Two MIT scientists, Frederick Sanders and John R. Gyakum, gave these intense and rapidly growing cyclone storms the name “bomb.”

In their paper “Synoptic-Dynamic Climatology of the ‘Bomb,’ ” Sanders and Gyakum define a “bomb” as a cyclone storm in which the barometric pressure at the center falls by at least 1 millibar per hour for 24 hours—a very steep and sudden drop.

The authors also described the “bomb” as a “predominantly maritime, cold-season event,” and said the “more explosive bombs” develop over the Atlantic (Monthly Weather Review, October 1980).

A phrase meaning the same thing, “weather bomb,” appeared in 1986, according to the Oxford English Dictionary. The OED defines it as as a rapidly developing severe storm “in which barometric pressure at the centre of the storm drops by at least 24 millibars over a 24-hour period at or north of 60˚ latitude.”

Here’s the OED’s earliest example: “In this positive feedback process, the storm rapidly intensifies into a weather bomb” (Science News, May 17, 1986).

The earliest example we’ve seen for “bomb cyclone” is from a 1987 scientific paper that uses the phrase “bomb cyclone case study” in reference to a 1984 paper by Gyakum. (“Rapid Surface Anticyclogenesis: Synoptic Climatology and Attendant Large-Scale Circulation Changes,” by Stephen J. Colluci and J. Clay Davenport, Monthly Weather Review, April 1987).

It should be noted here that the terms “bomb” and “Nor’easter” are not interchangeable. Not all Nor’easters become “bombs,” and not all “bombs” are Nor’easters, though the two weather patterns sometimes converge. A “bomb” is not a hurricane either, though in their 1980 paper Sanders and Gyakum said that “bombs” often have “hurricane-like features in the wind and cloud fields.”

In an interview Gyakum, who is now a professor of atmospheric science at McGill University, explained why “bomb” was used in the 1980 paper:

“I was a graduate student at the time [at MIT], and my adviser, who was the lead author, Frederick Sanders, actually coined the term. He had quite a bit of experience making forecasts for cyclones in the North Atlantic that were developing very rapidly. Oftentimes, we’d even say explosively. Given their explosive development, it was an easy path to take to just call these systems ‘bombs.’  … The name isn’t an exaggeration—these storms develop explosively and quickly” (The Washington Post, Jan. 24, 2018).

But even before large intense cyclone systems were called “bombs,” scientists had been using terms likening them to explosions.

For example, “cyclogenesis” (dating from the early 1920s) means the formation of a cyclone storm around a low-pressure area. And “explosive cyclogenesis” (early ’50s) refers to the kind in which pressure drops so steeply and rapidly—24 millibars in 24 hours, by definition—that the storm becomes what’s now called a “bomb.”

Even the term “bombogenesis,” another name for “explosive cyclogenesis,” was known to science in the late ’80s but didn’t show up in popular journalism until around 2015.

Here are Oxford’s earliest examples of the three terms—“cyclogenesis,” “explosive cyclogenesis,” and “bombogenesis”:

“Let us emphasize that any discussion of the so-called wave-theory of cyclogenesis will remain futile as long as the mathematical treatment of the subject is as incomplete as at present” (from the Swedish journal Geografiska Annaler [Geographical Annals], 1925).

“Wintertime conditions when the primary planetary wave activity is often initiated by explosive cyclogenesis in the troughs” (Meteorological Monographs, 1953).

“Climatology shows that a high frequency of ‘bombogenesis’ occurs over the ocean.” (From “Anatomy of a ‘Bomb’: Diagnostic Investigation of Explosive Cyclogenesis Over the Mid-West United States,” a master’s thesis by Michael E. Adams, North Carolina State University, 1989.)

Finally, “cyclone” came into English in the mid-19th century from the Greek words κύκλος (kyklos, circle) or κυκλῶν (kykloun, moving in a circle, whirling around), the OED says. It’s been used in three ways in English, the dictionary explains:

As first used, in 1848, “cyclone” was “a general term for all storms or atmospheric disturbances in which the wind has a circular or whirling course.”

Beginning in 1856 “cyclone” was also used in a more specific sense, for “a hurricane or tornado of limited diameter and destructive violence.”

The term as used in science today was first recorded in 1875, the OED says. The National Weather service, in its glossary, defines “cyclone” this way: “A large-scale circulation of winds around a central region of low atmospheric pressure, counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.”

We wrote a 2018 post about the etymology of “bomb,” so we won’t repeat ourselves. We’ll just add its meteorological definition, courtesy of the National Weather Service: “Popular expression of a rapid intensification of a cyclone (low pressure) with surface pressure expected to fall by at least 24 millibars in 24 hour.”

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