75th Anniversary of Gordon Dunn’s “isallobaric waves” paper

Gordon Dunn
Gordon Dunn

In June of 1940, Gordon Dunn published a paper in the Bulletin of the American Meteorological Society about the nature of disturbances in the Atlantic and their relationship to tropical cyclone formation.  While working as a junior hurricane forecaster at the Weather Bureau’s Jacksonville Hurricane Warning Center, Dunn analyzed daily weather maps for the Atlantic Ocean, and noticed displacements in the pressure field which were associated with disturbed weather.  He called them “isallobaric waves” since they appeared as horizontal waves on the isobar maps.  They seemed to be stable in structure as they moved from east to west from the coast of Africa to the Caribbean Sea, and were associated with a breakdown in the inversion layer common in the region.  They also provided the origins for many tropical cyclones, and he traced all of the hurricanes that formed in 1935, 1937, and 1938 to such waves.   This paper provided a new paradigm for tropical cyclogenesis.  Today isallobaric waves are called African Easterly Waves.

horizontal waves in the tropical Atlantic pressure field
Horizontal waves in the tropical Atlantic pressure field

Dunn, G.E., “Cyclogenesis in the Tropical Atlantic,” Bulletin of the American Meteorological Society, Vol. 21, No. 6, June 1940, p.215-229

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