Long Term Trends in the Radiative Heating Rates and Planetary Wave Activity in the Winter Polar Stratosphere

Recently, Hu and Tung (2002) used an energy budget analysis to study the relationships between ozone depletion, planetary wave activity, and the polar vortex in the late winter stratosphere. This study was carried out without explicitly including the radiation fields. We have completed the energy budget analysis using the radiation fields from the NCEP/NCAR reanalysis. Our study confirms Hu and Tung's conclusions with respect to the reduction in planetary wave activity and the cooling trend during the last two decades. Furthermore, our results definitively show that there is a positive trend in the net radiative heating during the same period. The primary cause for this trend was found to be the reduction in the long-wave radiation due to the negative trend in temperature. The increase in the net radiative heating is overwhelmed by a decrease in the dynamical heating (meridional heat transport), leading to the overall cooling trend seen in the polar region in late winter. Thus far, we are not able to find evidence in support of the hypothesis that ozone depletion strengthens the positive feedback loop involving the cooling of the polar stratosphere, increase of the meridional temperature gradient, strengthening of the polar vortex, reduction of planetary wave activity and decrease of meridional transport of heat and ozone.