INTERANNUAL VARIABILITY OF THE ANTARCTIC OZONE HOLE IN A GCM .1. THE INFLUENCE OF TROPOSPHERIC WAVE VARIABILITY

To study the interannual variability of the Antarctic ozone hole, a ph ysically realistic parameterization of the chemistry responsible for s evere polar ozone loss has been included in the GISS GCM. The ensuing ozone hole agrees well with observations, as do modeled surface UV inc reases of up to 42%. The presence of the ozone hole causes a reduction in lower stratospheric solar heating and an increase in upper stratos pheric descent and dynamical heating in the model, as expected. Both t he degree of ozone depletion and the dynamical response exhibit large interannual variability, however. These variations are driven by diffe rences in the midwinter buildup of tropospheric wave energy in the mod el, which affect the dynamics globally for several months according to the mechanism detailed herein. Starting by July, strong tropospheric wave activity lends to greater energy reaching the lower stratosphere, and therefore warmer temperatures, than in years with weak wave activ ity. The warmer temperatures persist throughout the austral spring, re sulting in ozone losses that are only similar to 80% of those seen in the years with weaker wave activity. Significant differences also occu r in the zonal Hind field, setting up conditions that ultimately affec t the propagation of wave energy in the spring. Differences in the pro pagation of wave energy lead to an October increase in upper stratosph eric dynamical heating that is more than three times larger in the yea rs with weak wave activity than in years with strong wave activity. Mo deled interannual variations in both upper stratospheric temperatures and ozone loss are of similar magnitude to observations, though the la rgest observed variations exceed those seen here, indicating that unfo rced variability likely plays a significant role in addition to period ic forcings such as the QBO. The results are in accord with observatio nal studies showing a strong anticorrelation between the interannual v ariability of tropospheric wave forcing and of the Antarctic ozone hol e, suggesting that midwinter tropospheric wave energy may be the best predictor of the severity of the ozone hole the following spring.