Polar Front

The polar front is the sloping boundary in the mid-latitudes between cold polar air and warmer subtropical air, where the steep horizontal temperature gradient supports the polar-front jet stream aloft by the thermal-wind relation. It is the principal birthplace of extratropical cyclones: waves grow on the front through baroclinic instability, developing the warm and cold fronts of mid-latitude depressions. The front and its storm track shift seasonally and meander with Rossby waves, lying near 50 to 60 degrees latitude on average. Its atmospheric meaning differs from the oceanic Polar Front of the Southern Ocean, a separate density-driven feature.