Ecoregions of the United States

Abstract

Climates of the polar domain, located at high latitudes, are controlled chiefly by polar and arctic air masses. In general, climates in the polar domain have low temperatures, severe winters, and small amounts of precipitation, most of which falls in the summer. Polar systems are dominated by a periodic fluctuation of solar energy and temperature, in which the annual range is far greater than the diurnal range. The intensity of the solar radiation is never very high compared with ecosystems of the middle latitudes and tropics.