Southern Hemisphere Stratospheric Warmings and Coupling to the
Mesosphere-Lower Thermosphere
Abstract
Twenty six years of MF radar wind measurements made from 1994 to 2019 at
Davis Station (68.6◦S, 77.9◦E) are used to study the mean re- sponse of
the mesosphere-lower thermosphere to stratospheric warmings in the
southern hemisphere. Warming events were detected using Modern- Era
Retrospective Analysis for Research and Applications (MERRA)-2 data with
a systematic search for reductions in the zonal-mean circulation at 60◦S
and corresponding increases in polar temperatures. Some 38 events were
identified, including the major warmings of 2002 and 2019, with an
average of 1 to 2 warmings per year. At the 10 hPa level, the polar cap
temperature increases ranged from 5 to 30 K, with a mean value of 11 K,
while the zonal wind speed reductions varied between -7 to -43 ms−1,
with −1 a mean value of -15 ms . Peak values occurred near 40 km.
Warmings occurred mainly between August and October, with a small peak
in oc- currence in April/May. The MF radar data showed an average
reduction in the mesospheric eastward winds of about 5-7 ms−1 at heights
near 75 km that occurred some 3-4 days prior to the changes in the
stratosphere. Warming events were driven by episodic intensifications in
planetary waves amplitudes, with quasi-stationary PW 1 being especially
important. Plane- tary wave Eliassen-Palm flux divergences show a
systematic behavior with time and height that is consistent with a
poleward residual circulation and downwelling over the pole prior to the
warming events and an equatorward flow and upwelling after the peak of
the events.