Simulation of the Present-Day Atmospheric Ozone, Odd Nitrogen, Chlorine and Other Species Using a Coupled 2-D Model in Isentropic Coordinates

Abstract

This paper documents our two-dimensional model which incorporates comprehensive radiative transfer and chemistry modules coupled with self-consistent dynamical transports. A simultaneous simulation of a range of chemical trace gas species with different photochemical time scales, latitudinal and vertical gradients, and with tropospheric or stratospheric sources is attempted and the result compared with available satellite and in situ observations. The 2-D model utilizes all zonally averaged physical equations of momentum, energy and mass, and self-consistently determines both its advective and diffusive transport parameters from the observed temperature specific to the period of observation. A major assumption in the formulation is that diffusive mixing is caused by large-scale planetary waves which act predominantly along isentropic surfaces. It is also assumed that it is planetary waves that drive the stratophere away from radiative equilibrium, resulting in diabatic vertical and meridional advective transport. It is in this way that energy, momentum and tracer budgets are interconnected. Family approximation is used and the transported species include Ox, NOy, N2O, Cly, CH4, CO, CFCs and HF. Partition within a family is calculated assuming photochemical equilibrium. Diurnal variation of nitrogen species is obtained by solving an ordinary differential equation analytically. The comparison of the model result with observations is very favorable. Some previously known common model deficiencies have largely been overcome. Simulation of climatological ozone, including the details of seasonal, latitudinal and vertical distributions, is especially successful using the present coupled model. The problem of NOy deficit in the equatorial lower stratosphere also appears to have been resolved, and a correct latitudinal profile for nitric acid column is obtained. We give physical reasons for the improvements in the model results and discuss possible explanations for the remaining systematic deficiencies, now occurring mostly in the model upper stratosphere and mesosphere, where breaking gravity waves may become an important transport process.