Decdal changes in stratosphere-troposphere wave coupling in the Southern Hemisphere, and the role of ozone depletion

Most discussions of the stratospheric role in SH climate change have emphasized zonal mean downward coupling, via changes in the Southern Annual Mode. We examine decadal variations in downward wave coupling which is a major downward coupling process in the SH winter and spring, both in observations and in the GEOS CCM. Wave-wave cross correlations using MERRA reanalysis, suggest stratosphere-troposphere downward wave coupling in the Southern Hemisphere has become stronger over the past 3 decades, with more downward reflection during September-December. Wave geometry diagnostics indicate this is due both to an earlier onset of downward reflection in September, and to reflection lasting longer into December as a result of the delay in vortex breakup, attributed to ozone loss. A suite of different GEOS simulations of the past and future are then used to understand the impact of ozone changes on downward wave coupling.