What is a bomb cyclone?
When it comes to weather, it is hard to sound more frightening than to call a storm a “bomb cyclone.”
But that is how weather experts are describing a huge winter storm that is hitting the U.S. East Coast this week.
From the northern state of Maine to Georgia in the south, the storm has brought high winds and heavy snow. Schools and government offices have closed because of the weather and thousands of flights have been cancelled.
But as fearsome as the storm is, it probably will not be as “explosive” as the name sounds.
Weather experts, or meteorologists, have used the term “bomb” for storms for many years. The word has a clear definition for weather experts, says University of Oklahoma meteorology professor Jason Furtado.
After “bomb cyclone” appeared in a Washington Post story this week, the weather term became popular, or “blew up,” on social media. It became a top trending topic. The same thing happened four years ago with the phrase “polar vortex” — another long-used weather term that was not well known to the public.
The technical term is “Bombogenesis.” Bomb cyclone is a shorter way of saying it, which is better for social media, says meteorologist Ryan Maue. He helped popularize “polar vortex” in 2014.
Although “bomb cyclone” sounds bad, Maue notes, nothing will actually explode.
Storm strength is measured by central pressure. The lower the pressure, the stronger it is. A storm is considered a “bomb” when the pressure drops quickly — at least 24 mililbars in 24 hours.
Around the world, about 40 to 50 bomb cyclones develop each year. However, most are over the open ocean and few people notice them.
“We use the term bomb,” Furtado said. “We (weather experts) know what it means, but I do think it gets a little hyped up.”
A bomb cyclone is, essentially, a powerful low-pressure system that rapidly intensifies. If that sounds a lot like a hurricane, you’re not too far off. The ‘bomb’ part of the name refers to the phenomenon when the pressure inside a storm cell falls so quickly that it gives the storm explosive strength.
What makes a storm a “bomb” is how fast the atmospheric pressure falls; falling atmospheric pressure is a characteristic of all storms. By definition, the barometric pressure must drop by at least 24 millibars in 24 hours for a storm to be called a bomb cyclone; the formation of such a storm is called bombogenesis.
Here is how it works: Deep drops in barometric pressure occur when a region of warm air meets one of cold air. The air starts to move, and the rotation of the earth creates a cyclonic effect. The direction is counterclockwise in the Northern Hemisphere (when viewed from above), leading to winds that come out of the northeast — a Nor’easter.
Bomb cyclone refers to a phenomenon expected to occur as this weather event unfolds. The official term is explosive cyclogenesis, which is actually really common. The ‘bombing’ occurs when a low pressure system’s central pressure falls 24 millibars in 24 hours or less. This refers to a low pressure system, which is basically when the atmospheric pressure at sea level is lesser than the surrounding area. This, along with wind, forms a, you guessed it, cyclone. Millibars are a measurement to describe pressure. Earth’s standard surface pressure is about 1013 millibars. The further it drops, the more intense the cyclone gets. This bomb cyclone that is being experienced from Florida to Maine could produce winds similar to that of a hurricane, but that is only an assumption.