The omega equation: Q-G interpretations of simple circulation features

Abstract

Quasi-geostrophic (Q-G) theory can be used to infer the vertical circulation associated with a synoptic distribution of pressure and temperature in much the same sense as geostrophic theory is used to infer a three-dimensional distribution of the horizontal circulation. For the purposes of subjective analysis, a diagnosis of the vertical circulation and implied surface development can be based on identifying the sign and magnitude of a geostrophic forcing function associated with the particular distributions of geopotential and thickness shown on a conventional 500 hPa analysis chart. Examples of idealised circulation features are used to demonstrate both the strengths and the weaknesses of this approach, with reference to an analysis based on three different methods of evaluating the geostrophic forcing.