Three-Dimensional Tracer Structure and Behavior as Simulated in Two Ozone Precursor Experiments

Abstract

The GFDL 11-level general circulation/tracer model is used for two experiments designed to prepare the way for a self-consistent model of atmospheric ozone. The first experiment invokes a very simple condition at the top model level, an instantaneous relaxation to a specified 10 mb average observed ozone value. The tracer is inert below the top level until it is removed in the lower troposphere. The second experiment introduces a simplified, but reasonably realistic ozone chemistry at the top level including Chapman, nitrogen and hydrogen loss processes. Below the top level, ozone is inert, and is removed in the lower troposphere by the same mechanism as in the first experiment. These two experiments, in spite of their very different middle stratospheres, show remarkably similar behavior in the lower stratosphere. A comparison of model values and fluxes with available observations shows general qualitative agreement as well as some notable discrepancies. In the second experiment, a detailed analysis of the processes affecting the 10 mb zonal-mean mixing ratio is presented. The results show that the mid-stratospheric ozone production and losses are strongly sensitive to circulation features, changing overhead sun angle and temperature. These various effects lead to some substantial interhemispheric and seasonal asymmetries in the ozone production. An analysis is performed of the transport processes leading to the pronounced poleward-downward slope of tracer isopleths. The results demonstrate that adiabatic and diabatic effects in the eddies, as well as diabatic effects in the zonal mean, all contribute importantly to the creation of these sloping surfaces. As an aid to tracer transport analysis, a Lagrangian ?non-transport? theorem is derived for an integration following a fluid particle. Some Lagrangian drift-type calculations are performed in the model January mean flow. The results show a slow but substantial particle convergence just to the cyclonic shear side of the time-mean jet stream axis. This is a region where the traditional zonal-mean budget analysis shows a very large cancellation between eddy and meridional circulation flux convergence. Also, the analysis demonstrates indirectly the very important contributions of transient disturbances to the movement of heat and tracers irreversibly into the stratospheric polar vortex.