The effect of dissipation on the vertical propagation of planetary waves in the vicinity of critical levels

Abstract

Planetary waves are excited at an initial time by the switch-on of vertical motion at the base of a stratified, isothermal atmosphere on a β-plane. Dissipation in the form of linear drag and Newtonian cooling is allowed for. Simple zonal wind profifes are used with linear shear and critical or zero wind levels. Dissipation rapidly dampens out residual time-dependent motion such that a steady state is reached in no more than a few weeks at all heights. Dissipation also permits the absorption of significant amounts of planetary-wave energy such that the basic flow cannot be considered invariant with time. The need for more accurate estimates of dissipation time scales in the upper atmosphere is pointed out. An important step toward this end will be a final solution to the problem of the photochemistry of ozone.