POLAR ANTICYCLONE

wind system associated with a region in which high atmospheric pressure develops over the northern areas of continental landmasses during the colder half of the year. The Siberian anticyclone is an example of a polar anticyclone, as is the weaker high-pressure area that forms over Canada and Alaska during the winter. Polar anticyclones are created by the cooling of surface layers of air over continental landmasses during the colder season. This cooling causes the air near the surface to become denser and, at the same time, causes an inflow of air at high levels to replace the denser, sinking air. These processes increase the mass of air above the surface, thus creating the anticyclone. The weather within the central regions of these anticyclones is typically clear and quite cold. Polar anticyclones frequently migrate to the south and east in the winter season, bringing cold waves to more southerly latitudes. The boundary separating the cold polar air from the warmer air to the south is called the polar front, and along this frontal surface many of the mid-latitude extratropical cyclones, or wave cyclones, form. See also front.