Simulations of zonal mean gravity wave drag short-term variability in the Southern Hemisphere mesosphere

Whole Atmosphere Community Climate Model simulations are used to investigate the short-term (<30-day) temporal variability in the midlatitude and high-latitude Southern Hemisphere mesosphere. We focus primarily on the short-term variability in zonal mean gravity wave drag and its influence on the mesosphere circulation and chemistry. The seasonal climatology from 36 years (1979-2014) of specified dynamics Whole Atmosphere Community Climate Model simulations reveals that the short-term variability of zonal mean gravity wave drag, which is quantified by the standard deviation over a 30-day window, in the Southern Hemisphere midlatitude mesosphere maximizes during December to March and September to November. The December to March enhancement is related to interhemispheric coupling during Northern Hemisphere sudden stratospheric warming events, and the enhancement during September to November is attributed to variability in the stratosphere and lower mesosphere zonal mean zonal winds that is driven by planetary wave activity in the Southern Hemisphere. Analysis of the simulations demonstrates that the short-term variability in mesospheric gravity wave drag leads to changes in the residual circulation, which subsequently introduces short-term variability in atomic oxygen (O) and nitrogen oxides (NOx). Comparison with the Northern Hemisphere reveals that the zonal mean short-term variability in the Southern Hemisphere during September to November is nearly as large (similar to 80-85%) as the maximum short-term variability in the Northern Hemisphere, which occurs during December to March. This demonstrates that although the Southern Hemisphere middle atmosphere is generally considered to be less disturbed than the Northern Hemisphere, there is still substantial short-term variability in the Southern Hemisphere mesosphere.