Tropopause Dynamics and Planetary Waves

Abstract

A simple model of the large-scale atmospheric circulation is studied. The model is based on the observation that the potential vorticity changes rapidly at the tropopause. This observation underlies the assumption that the potential vorticity on an isentropic surface, cutting through the tropopause, is piecewise uniform with a discontinuity at the tropopause. If it is assumed that the atmosphere's behavior can be described by the equivalent barotropic vorticity equation, a dynamical system is obtained that can be formulated entirely in terms of the discontinuity. First a zonally symmetric flow is studied to demonstrate that the model leads to quite realistic zonal velocity profiles. The behavior of infinitesimal amplitude (linear) waves superimposed on the basic zonal flow is then investigated. It is found that these waves are neutral and behave in many respects as Rossby?Haurwitz waves on a solid-body background flow. A numerical iteration procedure based on the technique of contour dynamics is used to construct families of finite amplitude (nonlinear) waves. The possible use of stationary waves of this kind as models for atmospheric blocking is discussed.