The Transport of Trace Chemicals by Planetary Waves in the Stratosphere Part 2: Transport of O3 and N2O by Transient Waves

Abstract

The transport of ozone and nitrous oxide by transient planetary wave in the stratosphere is studied on a midlatitude ?-plane with Newtonian cooling. The transport is found for chemically-inert traces when the mean-zonal state is forced from equilibrium by an initial switch-on of the wave at the lower boundary and returned to the initial state by radiative damping. In the absence of a critical level the net change in the tracer was due almost entirely to horizontal eddy flux convergence. However, this net change could also be described in terms of a one-ell Lagrangian-mean circulation. In the critical level case the net transport resulted from the superposition of the one-cell Legragian-mean circulation and the critical level circulation of Matsuno and Nakamura, as well as from particle mixing. It is concluded that transient waves are more important in tracer transport than steady waves because of the nonlinear dependence of transport on wave amplitude and Doppler-shifted frequency. Critical levels are important because they tend to localize wave energy absorption and therefore increase net transport in their vicinity. In addition, their presence restricts wave chew propagation to higher altitudes which results in correspondingly less net transport above the critical level height.