The polar highs are areas of high atmospheric pressure around the north and south poles, south polar high being the stronger one because land gains and loses heat more effectively than sea. The cold temperatures in the polar regions cause air to descend to create the high pressure (a process called subsidence), just as the warm temperatures around the equator cause air to rise to create the low pressure doldrums. Closely related to this concept is the polar vortex.
Surface temperatures under the polar highs are the coldest on Earth, with no month having an average temperature of above freezing. Regions under the polar high also experience very low levels of precipitation, which leads them to be known as "polar deserts".