Polar Front Theory

The account of extratropical cyclones as disturbances that form and grow along the boundary, or front, between two air masses of different temperature and origin, cutting the storm's life cycle into stages: wave formation, occlusion and decay. It was worked out at Vilhelm Bjerknes' Geophysical Institute in Bergen, chiefly by his son Jacob Bjerknes and Halvor Solberg, who published the theory in 1922 as Life Cycle of Cyclones and the Polar Front Theory of Atmospheric Circulation. Before it, forecasters read pressure maps largely by pattern-matching against past storms; the polar front theory gave them a physical model of why storms form and move, and its vocabulary, warm front, cold front, occlusion, is still how forecasters describe a storm today.