Polar cyclones (also known as Arctic Cyclones) are large areas of low pressure. They should not be confused with polar lows since people happen to use the same term for polar cyclones. Polar cyclones are usually 1,000 to 2,000 kilometers wide in which the air is moving in a spiral counterclockwise fashion in the northern hemisphere. The reason for the rotation is the same as tropical cyclones, the Coriolis effect. They also exist in places such as Greenland, the Eurasian Arctic area, and northern Canada, with about 15 cyclones per winter. Polar cyclones can form in any time of the year, although summer polar cyclones are usually weaker than the ones that form in the winter. Also, they are not closely studied and are rarely destructive since they happen in areas with little or no population.