  Sudden Stratospheric Warmings (SSW) affect the chemistry and dynamics of the
middle atmosphere. Major warmings occur roughly every second winter in the
Northern Hemisphere (NH), but has only been observed once in the Southern
Hemisphere (SH), during the Antarctic winter of 2002. Observations by the
Global Ozone Monitoring by Occultation of Stars (GOMOS, an instrument on board
Envisat) during this rare event, show a 40% increase of ozone in the nighttime
secondary ozone layer at subpolar latitudes compared to non-SSW years. This
study investigates the cause of the mesospheric nighttime ozone increase, using
the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community
Climate Model with specified dynamics (SD-WACCM). The 2002 SH winter was
characterized by several reductions of the strength of the polar night jet in
the upper stratosphere before the jet reversed completely, marking the onset of
the major SSW. At the time of these wind reductions, corresponding episodic
increases can be seen in the modelled nighttime secondary ozone layer. This
ozone increase is attributed largely to enhanced upwelling and the associated
cooling of the altitude region in conjunction with the wind reversal. This is
in correspondence to similar studies of SSW induced ozone enhancements in NH.
But unlike its NH counterpart, the SH secondary ozone layer appeared to be
impacted less by episodic variations in atomic hydrogen. Seasonally decreasing
atomic hydrogen plays however a larger role in SH compared to NH.
