Quantifying the Response Strength of the Southern Stratospheric Polar Vortex to Indian Ocean Warming in Austral Summer

A previous multiple-AGCM study suggested that Indian Ocean Warming (IOW) tends to warm and weaken the southern polar vortex. Such an impact is robust because of a qualitative consistency among the five AGCMs used. However, a significant difference exists in the modeled strengths, particularly in the stratosphere, with those in three of the AGCMs (CCM3, CAM3, and GFS) being four to five times as strong as those in the two other models (GFDL AM2, ECHAM5). As to which case reflects reality is an important issue not only for quantifying the role of tropical ocean warming in the recent modest recovery of the ozone hole over the Antarctic, but also for projecting its future trend. This issue is addressed in the present study through comparing the models' climatological mean states and intrinsic variability, particularly those influencing tropospheric signals to propagate upward and reach the stratosphere. The results suggest that differences in intrinsic variability of model atmospheres provide implications for the difference. Based on a comparison with observations, it is speculated that the impact in the real world may be closer to the modest one simulated by GFDL AM2 and ECHAM5, rather than the strong one simulated by the three other models (CCM3, CAM3 and GFS). In particular, IOW during the past 50 years may have dynamically induced a 1.0 degrees C warming in the polar lower stratosphere (similar to 100 hPa), which canceled a fraction of radiative cooling due to ozone depletion.