anticyclone

anticyclone region of high atmospheric pressure; anticyclones are commonly referred to as "highs." The pressure gradient, or change between the core of the anticyclone and its surroundings, combined with the Coriolis effect , causes air to circulate about the core in a clockwise direction in the Northern Hemisphere and a counterclockwise direction in the Southern Hemisphere. Near the surface of the earth the frictional drag of the surface on the moving air causes it to spiral outward gradually toward lower pressures while still maintaining the rotational direction. This outward movement of air is fed by descending currents near the center of the anticyclone that are warmed by compression as they encounter higher pressures at lower altitudes. The warming, in turn, greatly reduces the relative humidity, so that anticyclones, or "highs," are generally characterized by few clouds and low humidity. Such weather characteristics may extend over an area from a few hundred to a few thousand miles wide. Many low-level anticyclones are swept generally eastward by the prevailing west-to-east flow of the upper atmosphere, usually traversing some 500 to 1,000 mi (800-1,600 km) per day. Other anticyclones are permanent or seasonal features of particular geographic regions. The term anticyclone is derived from the fact that the associated rotational direction and general weather characteristics of an anticylone are opposite to those of a cyclone .

anticyclone Area of high atmospheric pressure around which air circulates. The direction of air circulation is clockwise in the Northern Hemisphere and anticlockwise in the Southern Hemisphere. Anticyclones are often associated with settled weather conditions. In middle latitudes, they bring periods of hot, dry weather in summer, and cold, often foggy, weather in winter.

anticyclone An area or system of high atmospheric pressure that has a characteristic pattern of air circulation, with subsiding air and horizontal divergence of the air near the surface in its central region. Continental-scale anticyclones form source regions for air masses. Winds are generally light. They flow clockwise around the centre in the northern hemisphere and anticlockwise in the southern hemisphere. A temperature inversion is common at the base of the air subsidence, and this restricts the vertical development of cloud. The systems are often slow-moving or stationary. Weather conditions are generally settled. Cold anticyclones form over continents in winter and over polar areas at any time, accompanied by strong inversions; in the clear air, pronounced frosts and very cold surface conditions result. Warm anticyclones (so called because of the warm, subsided air aloft) over land areas typically bring spells of settled and often warm weather. See also anticyclonic gloom.