Bjerknes, Jacob -

(1897-1975): Norwegian meterologist (son of Vilhelm Bjerknes, see above). His theory of polar fronts (in collaboration with Tor Bergeron) applied the term "front" to the boundaries between two air masses having different properties (temperature, vapor content, density). The polar front theory was used to explain the origin of cyclones (low-pressure centers) from interaction between warm and cold air masses in the northern Atlantic Ocean.