polar front The main boundary line between polar and tropical air masses along which depressions develop in mid latitudes, especially over the oceans. The front is in general displaced towards the equator in winter and the poles in summer, though large displacements in either direction take place over shorter periods in individual sectors of the hemisphere.

polar front The main boundary line between polar and tropical air masses along which depressions develop in mid latitudes, especially over the oceans. The front is in general displaced equatorwards in winter and polewards in summer, though large displacements in either direction take place over shorter periods in individual sectors of the hemisphere.