STUDIES OF THE MOTION AND DEVELOPMENT OF LONG WAVES IN THE WESTERLIES

Abstract

In order to subdue small scale irregular features of the atmospheric circulation and emphasize the large-scale flow patterns, five-day mean charts showing the pressure distribution at 10,000 feet are presented. It is shown qualitatively that the long waves of the westerlies which appear on these charts seem to behave in a manner suggested by a theoretical formula developed by Rossby. Examples are shown wherein complex combinations of troughs and ridges are brought about by different speeds of motion in different latitude belts. Some indications for the development of new troughs are discussed, wherein a rapid readjustment of circulation patterns becomes necessary over most of the hemisphere. Cases of blocking are described where an unexplained disturbance in the atmosphere moves slowly westward, bringing with it increases in mass and diminutions of the speed of the westerlies. In the second portion of the report evidence is presented to show that Rossby's formula for trough displacement is also verified quantitatively, although the displacements are greatly modified by convergence and divergence in the atmosphere. Furthermore, the data reveal a systematic decrease with time in the velocity of troughs, which can be explained by Rossby's theory after taking into account the existence of semipermanent trough or ridge systems in the general circulation due to solenoidal or topographic influences. Finally, the practical use of empirical displacement formulae is discussed.