Norway

Arnt Eliassen

1996 Balzan Prize for Meteorology

For his fundamental contributions to dynamic meteorology that have influenced and stimulated progress in this science during the past fifty years.

Since his first publication, On the motion of the air over a mountain ridge, Professor Eliassen (1915 – 2000) has devoted his research to many different problems of theoretical meteorology.
The research area where his work has been most influential is the theory of atmospheric fronts. He first theoretically described the stability properties of a rotating flow with vertical and horizontal density gradients. Later, he applied these arguments to atmospheric fronts, and he was the first to explain why frontal gradients are formed as a consequence of large-scale flow instabilities.

Furthermore, his investigations in the 1950’s were fundamental to the formation of models, which were finally applied in numerical weather forecasting. Another theoretical problem in this field was the geographical size needed for a limited area model. This work was done in co-operation with J. Charney, and the result provided an understanding of extremely important limitations for limited area models and contributed to the success of the first numerical weather predictions.
Through all these activities, Oslo University became an attraction for meteorologists engaged in numerical weather forecasting.

In textbooks of modem meteorology, his name appears mainly in connection with the so-called Eliassen-Palm (EP) fluxes. These fundamental fluxes were defined in a paper where vertical propagation of topographically generated wave energy in the atmosphere was investigated.
In the 1970’s, Eliassen devoted much of his attention to isentropic formulations of atmospheric models. The isentropic coordinate system is attractive from many points of view, but as yet it has not been used widely in numerical weather forecasting or climate simulations because of practical difficulties encountered at the earth’s surface where the boundary condition in such a model is difficult to handle. However, the isentropic coordinate system is used in many studies as a powerful tool in analyses of observed atmospheric circulations.
Arnt Eliassen is Professor emeritus since 1985, but he is continually active in his scientific field.