The zonally averaged circulation of the middle atmosphere.

Abstract

The steady-state, zonally averaged circulation of the middle atmosphere (15-125 km) is studied with a quasigeostrophic, numerical model that explicitly includes a self-consistent calculation of solar radiative heating die to 02 and 03 absorption, Newtonian cooling, Rayleigh friction, tropopause boundary conditions based on climatological averages, and the effects of vertically propagating planetary waves. The direct, radiatively driven pole-to-pole circulation at solstice is sufficient to account of the cold summer mesopause and warm isothermal winter mesosphere with associated zonal jets of realistic magnitude. The climatological heat and momentum fluxes associated with planetary wave number 2 have a negligible effect on the mean circulation. With planetary wavenumber 1 no steady-state solution could be obtained due to the formation of easterlies and hance critical layers in the winter mesosphere. also the radiative heating associated with secondary peaks in the 02 density at the mesopause could render the polar mesopause region convectively unstable. -Authors