A QUASI-GEOSTROPHIC MODEL OF THE WINTER STRATOSPHERIC CIRCULATION

Abstract

A six-level quasi-geostrophic model including radiative and photochemical processes in the manner suggested by Lindzen and Goody is run from a state of joint radiative-photochemical equilibrium for midwinter conditions. The spectral method is used to integrate the equations where all dependent variables are represented by a set of spherical harmonics with east-west wave numbers 0, 1, 2, 3, and 6 included. The winter storage of ozone in the polar lower stratosphere is simulated, and the importance of horizontal planetary scale transports and the vertical eddy diffusion of ozone is demonstrated. The rapid dissipation of upper stratospheric temperature disturbances by joint radiative-photochemical relaxation is discussed, and the importance of tropospheric forcing and nonlinear exchanges of kinetic energy between the planetary scale waves is demonstrated. The energetics of downward-propagating spontaneous warmings is discussed. A full-scale warming is triggered by strengthening the north-south lower tropospheric temperature gradient. Its main energy source is found to be a greatly increased forcing of the stratosphere from below.