arctic air Very cold air mass, generally formed north of the Arctic Circle. As air from this source moves southwards, it cools the regions in which it arrives; but being itself heated in the process it becomes convectively unstable. Polar lows sometimes form and the accompanying wintry precipitation is often heavy.

Arctic air A very cold air mass, generally formed north of the Arctic Circle. As air from this source moves southwards, it cools the regions in which it arrives; but being itself heated in the process it becomes convectively unstable. Polar lows sometimes form and the accompanying wintry precipitation is often heavy.