Observations of Fronts

Abstract

The introduction of the concept of fronts lies in a remarkably succinct paper by J. Bjerknes (1919) which in a mere seven pages provided the conceptual basis for a mode of synoptic analysis revolutionary in its time and pervasive yet today. This paper contained also an early expression of the fundamental idea that the ascent of warm air and the descent of cold, in the cyclone, was fundamental not only to the cyclone but to the general circulation of the atmosphere. To quote Bjerknes while examining Fig. 1, “The lines of flow in a cyclone have approximately the character of logarithmic spirals. By increasing (the) number of observations, however, several aberrations from the regular spiralic shape appear. Among a multitude of details, certain characteristic traits seem to return more or less markedly for all cyclones yet examined.