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Posted by on Oct 15, 2018 in TellMeWhy |

What Is an Anticyclone?

What Is an Anticyclone?

An anticyclone (that is, opposite to a cyclone) is a weather phenomenon. The name anticyclone was first introduced by Sir Francis Galton, the English meteorologist, in 1861 to describe weather conditions opposite to those of a cyclone. Anticyclones are characterized by fine weather and weak winds. In weather maps and climatic charts, anticyclones appear as a region in which the pressure is higher than in its surroundings.

So when the weather forecaster starts to talk about anticyclones you can be prepared for the weather to remain stable for some time, usually sunny and with occasional light rain. In a cyclone or low-pressure area the winds circulate anti-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Cyclones are usually areas of strong, violent winds and indicate bad weather.

Anticyclone is defined by the United States National Weather Service’s glossary as “a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere”. Effects of surface-based anticyclones include clearing skies as well as cooler, drier air.

weather maps

Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base.

Anticyclones aloft can form within warm core lows such as tropical cyclones, due to descending cool air from the backside of upper troughs such as polar highs, or from large scale sinking such as the subtropical ridge. The evolution of an anticyclone depends on a few variables such as its size, intensity, moist-convection, Coriolis force etc.

Content for this question contributed by Vincent Majerowicz, resident of Healdsburg, Sonoma County, California, USA