Radiative‐dynamic effects of the antarctic ozone hole and chemical feedback

Abstract

AbstractA southern hemisphere winter/spring is simulated with the Coupled Stratosphere‐Mesosphere Interactive Chemistry model, a mechanistic model of the middle atmosphere with an interactive chemistry scheme. Simulations are initialized and forced at the lower boundary with dynamic fields taken from UK Meteorological Office assimilations for 1992. Radiative and dynamic effects of ozone depletion are investigated by comparing runs that include heterogeneous chemistry and hence develop an ozone hole, with otherwise identical control runs with no heterogeneous chemistry and no ozone hole. Temperatures in the ozone hole and control runs start to diverge from around mid‐September; by late October the lower stratosphere is up to ∼12 K cooler when an ozone hole is present. In the mid and upper stratosphere, a strengthened general circulation and an enhanced radiative heating rate in the ozone‐depleted runs lead to slightly higher temperatures at the high southern latitudes than in the control runs. the initially smooth evolution of the temperature difference at the upper levels is interrupted in mid‐October by more transient events associated with planetary‐wave activity.The feedback onto the chemistry of the physical changes wrought by using the depleted ozone in the radiative calculations is investigated by comparing runs of a chemical transport model forced by winds and temperatures calculated with and without an ozone hole. the ozone‐hole induced cooling does not change the spatial extent of the chlorine and bromine activation, and only slightly extends its duration. Consequently, the depth and size of the ozone hole are unchanged by chemical feedback. Local deficits in the ozone column of up to ∼30 Dobson units which arise in the cooler run in October are due to differences in horizontal transport. the increased diabatic descent resulting from using the depleted ozone for the radiation calculations does not significantly alter the vertical transport of polar ozone, the rate of which is low compared with the rate of chemical ozone destruction.