Response of the extratropical middle atmosphere to the September 2002 major stratospheric sudden warming

Abstract

The effects of a major stratospheric sudden warming (SSW) at extratropical latitudes have been investigated with wind and temperature observations over a Brazilian station, Cachoeira Paulista (22.7°S,45°W) during September–October 2002. In response to the warming at polar latitudes a corresponding cooling at tropical and extratropical latitudes is prominent in the stratosphere. A conspicuous signature of latitudinal propagation of a planetary wave of zonal wavenumbers 1 and 2 from polar to low latitude has been observed during the warming period. The polar vortex which split into two parts of different size is found to travel considerably low latitude. Significant air mass mixing between low and high latitudes is caused by planetary wave breaking. The meridional wind exhibits oscillations of period 2–4days during the warming period in the stratosphere. No wave feature is evident in the mesosphere during the warming period, although a 12–14day periodicity is observed after 2weeks of the warming event, indicating close resemblance to the results of other simultaneous investigations carried out from high latitude Antarctic stations. Convective activity over the present extratropical station diminishes remarkably during the warming period. This behavior is possibly due to destabilization and shift of equatorial convective active regions towards the opposite hemisphere in response to changes in the mean meridional circulation in concert with the SSW.