An anti-cyclone also known as a high pressure area is a large atmospheric circulation system with the wind flowing clockwise around it in the Northern Hemisphere, an counter-clockwise in the Southern Hemisphere.
Anticyclones form from air masses cooling more than their surroundings, which causes the air to contract slightly making the air more dense. Since dense air weighs more, the weight of the atmosphere overlying a location increases, causing increased surface air pressure.
The strongest anticyclones occur over snow-covered portions of Asia and North America in the winter when clear, dry air masses cool from a loss of infrared radiation, while little sunlight is absorbed to offset that infrared cooling.
Topics: Anticyclone • Atmosphere of Earth • Atmosphere of Jupiter • Atmospheric circulation • Atmospheric dynamics • Cyclone • High-pressure area • Low-pressure area • Meteorology • Physical geography • Vortices • Weather hazards