A new look at the ω‐equation

Abstract In the conventional quasi‐geostrophic form of the ‘omega’‐equation, the forcing of vertical velocity is usually expressed as the sum of two terms associated respectively with vorticity and temperature advection. Consideration of each term in isolation is misleading and there can be a large degree of cancellation. On the other hand, in Sutcliffe's development theory, this forcing is, in effect, represented by a single term. However, this is achieved at the expense of neglecting another term which is dominant in frontal regions. An investigation, based upon the governing equations, of the manner in which geostrophic balance tends to destroy itself, reveals a simple, concise, one‐term representation of the geostrophic forcing of ageostrophic motion. Many of the traditional synoptic rules are then simple deductions from this theory. An application of the theory in the case of a rapidly developing system is demonstrated using a 700mb chart.