Summer hemisphere differences in temperature and transport in the lower stratosphere

Abstract

Lower stratospheric temperatures during southern hemisphere summer are found to be warmer than at the same latitude poleward of the equator during northern hemisphere summer. Coincident with such warmer temperatures is a stronger residual circulation as calculated from radiative heating rates computed using as input observations from the Upper Atmospheric Research Satellite (UARS). Such a summertime asymmetry in extratropical downwelling in the lower stratosphere does not appear in the residual circulation calculated via the downward control technique based on National Meteorological Center (NMC) analyses. Computing the residual circulation with the downward control technique using Eliassen‐Palm flux divergences based on assimilated winds and temperatures does yield the above noted summertime hemispheric asymmetry in downward extratropical mass transport, although not as pronounced as with the radiative calculation. It is proposed that smaller‐scale zonal forces due to gravity waves, absent in the NMC downward control calculation, may be important for driving the southern hemisphere summer circulation in the lower stratosphere.