The  polar  high  in  winter  is  not  a  cell  centered directly  over  the  North  Pole,  but  appears  to  be  an extension  of  the  Asiatic  high  and  often  appears  as  a wedge extending from the Asiatic continent. The cell is displaced toward the area of coldest temperatures—the Asiatic continent. In summer, this high appears as an extension  of  the  Pacific  high  and  is  again  displaced toward the area of coolest temperature, which in this case is the extensive water area of the Pacific. In winter over North America, the most significant feature is the domination by a high-pressure cell. This cell  is  also  due  to  cooling  but  is  not  as  intense  as  the Asiatic cell. In summer, the most significant feature is the so-called heat low over the southwestern part of the continent,  which  is  caused  by  extreme  heating  in  this region. MIGRATORY SYSTEMS General  circulation,  based  on  an  average  of  wind conditions, is a more or less quasi-stationary circulation. Likewise, much of the secondary circulation  depends  on  more  or  less  static  conditions that, in turn, depend on permanent and semi permanent high and low-pressure areas. Changes in the circulation patterns  discussed  so  far  have  been  largely  seasonal. However,   secondary   circulation   also   includes   wind systems   that   migrate   constantly,   producing   rapidly changing  weather  conditions  throughout  all  seasons, especially   in   the   middle   latitudes. The   migratory circulation   systems   are   associated   with   air   masses, fronts, cyclones, and anticyclones. These are covered in detail in the next unit. Anticyclones An anticyclone (high) is an area of relatively high pressure with a clockwise flow (wind circulation) in the Northern Hemisphere and counterclockwise flow in the Southern Hemisphere. The windflow in an anticyclone is slightly across the isobars and away from the center of  the  anticyclone.  (See  fig.  3-15.)  Anticyclones  are commonly called highs or high-pressure areas. 3-16 80 80 120 120 120 120 160 160 160 160 80 80 40 40 0 0 40 40 80 80 1012 1012 1016 40 20 0 1012 1020 1020 H 1012 60 60 0 20 40 1012 H 1020 1016 1012 H 1020 1601016 `1012 L H 1016 1020 1020 H AG5f0314 L H 1020 1016 1020 1020 1012 1016 1016 1012 1020 ¹⁰²⁰1016 1016 EQUATORIAL LOW PRESSURE  BELT Figure 3-14.—Average annual pressure distribution chart. HIGH ANTICYCLONIC CIRCULATION AG5f0315 Figure 3-15.—Anticyclone.