Abstract
SYNOPSIS
The general circulation of the atmosphere considered as a circular vortex, as postulated by Professor Bjerknes is briefly discussed; it is pointed out that surfaces of discontinuity must arise along the margins of air streams moving equatorward and poleward, respectively, and that under certain conditions these surfaces of discontinuity are unstable, a wave motion sets in with the cold air pressing southward in the rear of warmer air moving northward; thus a series of wave motions in the atmosphere originate and are propagated eastward.
The criteria are given for fixing the position of that surface of discontinuity to which the name “polar front” has been applied, and the effect of differing conditions which arise in nature in connection with the changes of position of the polar front is discussed in some detail. The occurrence of cyclones in groups or families of two to six, with four being the most probable number according to the statistics of the Norwegian weather maps, is discussed and several families are considered in detail.
The forecasting of the weather of Norway by the Bjerknes theory, as carried on at Bergen, is described for representative weather types and finally an attempt is made to apply the Bjerknes theory to the synoptic weather maps of the U. S. Weather Bureau for January, 1921. The observational material printed on these maps lacks much of the data available in the Norwegian Meteorological Office, nevertheless surfaces of discontinuity can be traced and more exact and detailed forecasting seems to be possible when more detailed observational data are available.
