GENERALIZED CRITERIA FOR DYNAMIC INSTABILITY

Abstract

The ?parcel? method of treating dynamic instability is extended to the case of an arbitrary flow pattern. The criteria for instability become relatively complex and depend on the three-dimensional gradients of temperature and geostrophic wind, as well as on the latitude. Fundamentally different types of instability and stability may arise; these are illustrated by typical examples. Methods for the computation of the various terms in the fundamental stability-criterion parameters are presented, and these methods, as well as the generalized criteria themselves, are extended to the case of saturated air. It is suggested that marked quasi-horizontal, or dynamic, instability will superimpose a strong field of ?perturbation divergence? on the ambient field of mass divergence and hence should be a significant factor in the weakening of anticyclones and the formation and deepening of cyclones.