QUANTITATIVE ANALYSIS OF FACTORS INFLUENCING PRESSURE CHANGE

Abstract

The contribution to density change made by local compression or expansion, advection, and vertical motion, and by horizontal mass divergence or convergence is determined for 132 cases chosen during a period of anticyclogenesis above a polar anticyclone and during two periods of cyclogenesis. The density change in the layer two or three kilometers in thickness just above the tropopause is shown to contribute most to pressure change at the ground. This density change may be considered to be the result either of advection in the lower stratosphere or of the excess of horizontal mass divergence over vertical mass divergence. Advection in the lower stratosphere is found to be closely related to local pressure change and to vertical motion in the upper and middle troposphere: downward motion accompanies rising pressure and advection of denser air and upward motion accompanies falling pressure and advection of lighter air.