The significance of vertical stability in synoptic development

The connection between the development of depressions and anticyclones and the degree of vertical stability of the atmosphere is examined. It is concluded that in middle latitudes the damping due to stability is not important in the largest‐scale circulations of diameter greater than about 2,000 km, but has controlling significance for systems of diameter less than about 1,000 km. The difference in the rate of development between an ordinarily stable and a neutral atmosphere may be ten‐fold or more for the smaller systems. A very small degree of instability in depth will permit small‐scale cyclonic development to proceed rapidly. Furthermore, the damping effect of atmospheric stability is inversely proportional to the square of the Coriolis parameter. At 10° latitude, for example, the effect becomes dominant for all practical diameters, and it would appear difficult for cyclones or anticyclones of any reasonable size to develop significantly in low latitudes, with the exception of cyclones in a vertically unstable atmosphere.