Ask the meteorologists: what is a cyclone? | Weather

A house is in ruins after Cyclone Batsirai hit Madagascar on February 10, 2022.

Q: What is a cyclone?

A: A cyclone is a general term for a weather system in which the winds turn inward toward an area of ​​low atmospheric pressure.

For major weather systems, the circulation pattern is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Types of cyclones include tropical cyclones, extratropical cyclones, and tornadoes.

A tropical cyclone is a rotating low-pressure weather system that has organized thunderstorms but no fronts. They form on the warm waters of the ocean.

Tropical cyclones with maximum sustained surface winds below 39 mph are called tropical depressions. Those with maximum sustained winds of 39 mph or more are called tropical storms. When a storm’s maximum sustained winds reach 74 mph, they are called hurricanes or typhoons. Hurricanes form over the Atlantic Ocean or the Caribbean Sea; typhoons form over the western Pacific Ocean.

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Extratropical cyclones are low pressure systems that form outside the tropics in response to chronic instability in westerly winds. Because this instability depends on large horizontal contrasts in temperature, concentrated regions of temperature change called fronts characterize extratropical cyclones.

These storms populate the mid and high latitudes, north of 35 degrees latitude in the Northern Hemisphere, and are therefore also referred to as “mid-latitude cyclones”. If the barometric pressure of a mid-latitude cyclone drops by at least 1 millibar per hour for 24 hours, the storm is called a “bomb cyclone”.

A tornado is a rapidly rotating column of air that extends downward from a thunderstorm to the ground. The most violent tornadoes are capable of enormous destruction with winds of up to 300 mph.

Tornadoes form in regions of the atmosphere that have abundant warm, moist air near the surface with drier air above, and a change in wind speed and direction with height above. above ground.

“Weather Guys” Steve Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison.

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