Planetary and gravity waves in the mesosphere and lower thermosphere region over Tirunelveli (8.7°N, 77.8°E) during stratospheric warming events

Abstract

An investigation of planetary wave (PW) activities in UKMO (UK Meteorological Office) winds during winter of the years 1998-99 and 2005-06, when major sudden stratospheric warming (SSW) events occurred, shows that the amplitude of PW of zonal wave number 1 is considerably reduced in zonal winds, when the warming event is onset and the reduced activity persists several days even after the end of the SSW event. Similar reduction of PW activity in zonal winds has been observed in the wavelet spectrum of MF radar zonal winds at altitudes 84-98 km over Tirunelveli (8.7°N, 77.8°E). During this period of reduced PW activity, enhancement in gravity wave activity is observed during 2005-06 and is not observed during 1998-99 and the mean meridional winds change to more equatorward during 2005-06 and remain poleward during 1998-99. In accordance with TIME-GCM results, our observations show that the wind reversal occurred in the stratosphere during major warming events allows more eastward gravity waves to propagate into the mesosphere and lower thermosphere (MLT) region, which causes changes in the meridional circulation from poleward to equatorward.