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Bjerknes, Vilhelm (Firman Koren)

stage masses air occlusion

[byerk nes] (1862–1951) Norwegian meteorologist: pioneer of dynamical meteorology.
Depression–plan view of the six idealized stages in the development and final occlusion of a depression along a polar front in the Northern Hemisphere. Stage 4 shows a well developed depression system and stage 5 shows the occlusion. The cross-section (7) is taken along the line AB in stage 4. The cloud types are: Cb – cumulonimbus; As–altostratus; Ac–altocumulus; Cs–cirrostratus; Ns–nimbostratus; Ci–cirrus.

Bjerknes’s father was professor of mathematics at the Christiania University (now Oslo), and Bjerknes himself held professorships at Stockholm and Leipzig before founding the Bergen Geophysical Institute in 1917. Through his hydrodynamic models of the atmosphere and the oceans Bjerknes made important contributions to meteorology, and in 1904 showed how weather prediction could be achieved numerically using mathematical models. During the First World War Bjerknes established a network of weather stations throughout Norway, the results allowing him and his collaborators (who included his son, Jacob (1897–1975), and ) to develop their theory of polar fronts. They demonstrated that the atmosphere is composed of distinct air masses with different characteristics, the boundaries between such air masses being called ‘fronts’. Their Bergen frontal theory, as it became known, explains how cyclones are generated over the Atlantic where warm and cold air masses meet.

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