Interannual Variability of the Antarctic Ozone Hole in a GCM. Part I: The Influence of Tropospheric Wave Variability

Abstract

To study the interannual variability of the Antarctic ozone hole, a physically realistic parameterization of the chemistry responsible for severe polar ozone loss has been included in the GISS GCM. The ensuing ozone hole agrees well with observations, as do modeled surface UV increases of up to 42%. The presence of the ozone hole causes a reduction in lower stratospheric solar heating and an increase in upper stratospheric descent and dynamical heating in the model, as expected. Both the degree of ozone depletion and the dynamical response exhibit large interannual variability, however. These variations are driven by differences in the midwinter buildup of tropospheric wave energy in the model, which affect the dynamics globally for several months according to the mechanism detailed herein. Starting by July, strong tropospheric wave activity leads to greater energy reaching the lower stratosphere, and therefore warmer temperatures, than in years with weak wave activity. The warmer temperatures persist throughout the austral spring, resulting in ozone losses that are only ?80% of those seen in the years with weaker wave activity. Significant differences also occur in the zonal wind field, setting up conditions that ultimately affect the propagation of wave energy in the spring. Differences in the propagation of wave energy lead to an October increase in upper stratospheric dynamical heating that is more than three times larger in the years with weak wave activity than in years with strong wave activity. Modeled interannual variations in both upper stratospheric temperatures and ozone loss are of similar magnitude to observations, though the largest observed variations exceed those seen here, indicating that unforced variability likely plays a significant role in addition to periodic forcings such as the QBO. The results are in accord with observational studies showing a strong anticorrelation between the interannual variability of tropospheric wave forcing and of the Antarctic ozone hole, suggesting that midwinter tropospheric wave energy may be the best predictor of the severity of the ozone hole the following spring.