Polar Vortex, Bomb Cyclone and Other Weather Terms, Explained

Many of the latest buzzwords in weather forecasting – “polar vortex”, “bomb cyclone” – describe natural phenomena that are not new, or even necessarily more common than before, even if climate change, in general, has led to more extreme weather events. But the terminology is more widely disseminated, sometimes with precision, sometimes less.

polar vortex

According to the National Weather Service, a polar vortex “is a large area of ​​low pressure and cold air surrounding the Earth’s two poles. It ALWAYS exists near the poles, but weakens in summer and strengthens in winter. The term “vortex” refers to the counterclockwise airflow that helps keep cooler air near the poles. The polar vortex develops quite regularly during the winter in the northern hemisphere, carrying arctic air towards the United States.

Bomb Cyclone

A bomb cyclone is a rapid pressure drop in a mass of low-pressure air — “of at least 24 millibars in 24 hours,” said John Gyakum, a meteorologist at McGill University who helped invent the term in the 1980s. As the pressure difference, or gradient, increases between the low-pressure air mass and the neighboring high-pressure air mass, the winds sharply intensify. This process of rapid intensification is known as bombogenesis.

atmospheric river

Atmospheric rivers “are narrow regions of the atmosphere that carry much of the moisture from the tropics to northern latitudes,” according to the National Oceanic and Atmospheric Administration, or NOAA. “Atmospheric rivers are part of the water cycle of Earth’s oceans and are closely linked to both water supply and flood risk.”

Some atmospheric rivers can lead to dangerous weather conditions, but many others don’t, Dr Gyakum said, adding: “A lot of these cases can just move and meander around the globe and not do much. at all”.

Pineapple Express

A semi-famous example of a strong atmospheric river is the Pineapple Express, so-called “because moisture builds up in the tropical Pacific around Hawaii and can hit the west coasts of the United States and Canada with heavy rain and snow,” according to NOAA.

(In 2008, Seth Rogen starred in a comedy called “Pineapple Express,” in which a drug dealer witnesses a murder and runs from an assassin and a corrupt cop, but it had no noticeable impact on the weather. .)

ARKStorm

A “‘megastorm’ scenario that was originally expected to occur once every 1,000 years, according to the United States Geological Survey, but is now expected to “become more frequent and intense due to climate change.” The name comes from the combination of “AR” (atmospheric river) and “k” (for 1000). One such megastorm occurred in California in 1861-1862, “and there is no reason to believe similar events will not occur again,” the agency said.