A polar vortex is an upper level low-pressure area lying near the Earth's poles. There are two polar vortices in the Earth's atmosphere, overlying the North and South Poles. Each polar vortex is a persistent, large-scale, low-pressure zone that rotates counter-clockwise at the North Pole and clockwise at the South Pole, i.e., both polar vortices rotate eastward around the poles. The bases of the two polar vortices are located in the middle and upper troposphere and extend into the stratosphere. Beneath that lies a large mass of cold, dense Arctic air.