A powerful storm described as a “once-in-a-decade” event recently ripped through the Pacific Northwest, causing major power outages, major damage and at least two deaths. Evidence suggests that such storms, called bomb cyclones, are becoming more frequent, raising questions about the role of climate change as a potential driver.

Powerful low pressure system

Terrifying satellite images captured a powerful low pressure system swirling about 300 miles off the coast of Washington. The system, known as a “bomb cyclone” due to its extremely rapid drop in atmospheric pressure that increased its strength, hit Northern California, the Pacific Northwest and British Columbia with hurricane-force winds and heavy rain. Tens of thousands of houses were left without electricity, trees were uprooted, and at least two people lost their lives.

What is a bomb cyclone?

The term “bomb cyclone” originated as slang to describe a rapidly intensifying extratropical hurricane, similar to a rapidly intensifying hurricane.

“The term has been around for about 80 years, but it became popular and formalized 40 years ago when it entered the published literature,” said Brian McNoldy, senior scientist at the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Sciences. .

Authors of the article “Synoptic-dynamic climatology of the bomb” published in the October issue of the journalMonthly Weather Review» In 1980, the American Meteorological Society called this weather event a bomb because it was developing “with a ferocity we rarely see above ground.”

“Another term used to describe this is explosive cyclogenesis – the rapid formation and development of a tornado,” McNoldy said. “To officially qualify as a bomb, the minimum central pressure must fall by at least 24 millibars in 24 hours at 60 degrees latitude or by at least 14 millibars in 24 hours at 30 degrees latitude.”

Differences between hurricane bombs and hurricanes

Although satellite images of the bomb tornado taken recently by the National Oceanic and Atmospheric Administration’s GOES 18 satellite are similar to tornado images, the two systems are structurally different. Hurricanes are vertical, their structure extending evenly from the ocean surface to the upper layers of the atmosphere. This vertical alignment allows for efficient wind flow and amplification.

Ben Kirtman, professor of atmospheric sciences and Middleton III professor at the William R. Rosensteel School.

“What’s happening in the upper atmosphere is to the west of what’s happening at the surface, and it’s that vertical tilt that is so critical to cyclone development.” “And so wind shear is the critical source of energy for tornado development, unlike tornadoes where it’s vertical, and the energy source for tornadoes is the warm water underneath.”

A general characteristic of winter weather

Eruption cyclones are winter storms that usually occur between October and March. They also form off the East Coast of the United States, where the infamous New England nor’easters are generally classified as bomb hurricanes.

A powerful bomb cyclone that recently hit the Pacific Northwest eventually merged with an atmospheric river (a long, narrow band of water vapor that carries atmospheric moisture from the tropics to colder regions). Meteorologists call such a storm a once-in-a-decade storm.

Data from the National Weather Service shows such weather systems are becoming more common, especially on the East Coast. Between 1980 and 2020, the number of bomb hurricanes in the Atlantic basin increased by nearly 40 percent.

Climate change and hurricane bombing

The question arises: Are climate changes contributing to the increase in bomb cyclones? The answer is complicated. Kirtman noted that this was likely due to an increase in ocean temperature. He explained that as the climate system warms, high latitudes warm faster than low latitudes, and that the energy for the mid-latitude cyclone system comes from the contrast between north and south.

“And your first reaction would be: ‘If the higher latitudes are warmer than the southern latitudes, there’s less energy for those hurricanes, there’s less temperature contrast.’ But that’s not the whole story,” Kirtman said.

‘The problem is what happens when you weaken the temperature gradient at the polar equator; you get a wavier pattern in the mid-latitude wind flow. That means because it’s wavier it can absorb cold air; we get bigger dips.’ “So cold air comes in from further south, and that sets off mid-latitude hurricanes. It is the injection of cold air that starts them. So we can increase the number of these systems.”