Weakening of Antarctic stratospheric planetary wave activities in early austral spring since the early 2000s: a response to sea surface temperature trends

Abstract

Using multiple reanalysis datasets and modeling simulations, the trends of Antarctic stratospheric planetary wave activities in early austral spring since the early 2000s are investigated in this study. We find that the stratospheric planetary wave activities in September have weakened significantly since the year 2000, which is mainly related to the weakening of the tropospheric wave sources in the extratropical Southern Hemisphere. As the Antarctic ozone also shows clear shift around the year 2000, the impact of ozone recovery on Antarctic planetary wave activity is also examined through numerical simulations. Significant ozone recovery in the lower stratosphere changes the atmospheric state for wave propagation to some extent, inducing a slight decrease in the vertical wave flux in upper troposphere and lower stratosphere (UTLS). However, the changes in the wave propagation environment in the middle and upper stratosphere over the subpolar region are not significant. The ozone recovery has a minor contribution to the significant weakening of stratospheric planetary wave activity in September. Further analysis indicates that the trend of September sea surface temperature (SST) over 20∘ N–70∘ S is well linked to the weakening of stratospheric planetary wave activities. The model simulations reveal that the SST trend in the extratropical Southern Hemisphere (20–70∘ S) and the tropics (20–20∘ S) induce a weakening of the wave 1 component of tropospheric geopotential height in the extratropical Southern Hemisphere, which subsequently leads to a decrease in stratospheric wave flux. In addition, both reanalysis data and numerical simulations indicate that the Brewer–Dobson circulation (BDC) related to wave activities in the stratosphere has also been weakening in early austral spring since the year 2000 due to the trend of September SST in the tropics and extratropical Southern Hemisphere.