anticyclone(redirected from anticyclones)
Also found in: Dictionary, Thesaurus.
a region in the atmosphere characterized by increased atmospheric pressure. The pressure distribution in anticyclones is represented on charts by concentric closed isobars (lines of equal pressure) of an irregular, approximately oval shape. The highest pressure is at the center of the anticyclone; it decreases toward the periphery. The pressure at the center of an anticyclone at sea level reaches 1,025–1,040 millibars (mbar), and sometimes (for example, in Asia during the winter) as high as 1,070 mbars. (Average pressure at sea level is 1,010–1,015 mbar; 1,000 mbar ≈ 750 mmHg ≈ 1.02 kg force per sq cm.)
Along with cyclones, anticyclones are formed continuously in the troposphere (the lower part of the atmosphere). Both are part of the general atmospheric circulation, creating inter-latitudinal exchange of air masses. During the year many hundreds of anticyclones develop in each hemisphere. The duration of an anticyclone is several days; in some cases, even weeks. Both cyclones and anticyclones move in the direction of the general exchange of air in the troposphere—that is, from west to east—and in the process are deflected toward the lower latitudes. The average speed of movement of anticyclones is approximately 30 km/hr in the northern hemisphere and approximately 40 km/hr in the southern; however, anticyclones frequently remain almost stationary. In the northern hemisphere, the winds in an anticyclone move in a clockwise direction around the center, and in the southern hemisphere, in a counterclockwise direction, forming a gigantic whirlwind. The diameter of anticyclones is on the order of thousands of km.
Above the so-called friction layer—that is, above 1,000 m on the average—the wind in the anticyclone blows almost entirely along the lines of the isobars; however, in the friction layer the wind is deflected out from the isobars—at the earth’s surface, at an angle of approximately 30°. This flow of air from the anticyclone in the lower layer is accompanied by an influx of air into the anticyclone in the upper layers of the atmosphere and by its gradual settling and subsiding of the anticyclone. In subsiding, the air is heated adiabatically and becomes more unsaturated. Therefore the temperature of the troposphere in an anticyclone increases (only during the winter immediately above the land surface can the temperature be very low) and there is little overcast, and as a rule, no precipitation. The winds in the interior of the anticyclone are weak; however, they increase at the periphery.
As the degree of development and the temperature of the anticyclone increase, so does its height: the closed isobars appear in increasingly higher layers of the troposphere, and even in the lower stratosphere. The stratosphere in anticyclones begins at a higher altitude than in cyclones, and its temperature is lower.
S. P. KHROMOV