The polar vortex is a vast area of low pressure and cold air that surrounds both of Earth's geographic poles. It is most pronounced during the winter, but persists, to a lesser extent, throughout the year. At the surface, the polar vortex is typically centered near 75°N latitude and 90°W longitude. The winds within the vortex rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The jet stream is located at the southern boundary of the polar vortex, and it separates the cold air of the polar vortex from the warmer air of the subtropics.