Studies of the dynamical coupling to the equatorial middle atmosphere

Abstract

The dynamics of the low latitude middle atmosphere in the context of sudden newlinestratospheric warming (SSW) signature and its effects is investigated using Medium newlineFrequency (MF) radar at Tirunelveli (8.7oN, 77.8oE), lidar from Gadanki (13.5oN, 79.2oE), newlineSABER/TIMED satellite measurements and UK met office assimilated data sets. Mean newlinewinds, planetary wave variability and gravity waves activities are investigated during SSW newlineevents in the middle atmosphere over tropical region. SSW events were detected using newlineNCEP reanalysis data for 17 years (1992-2009) during NH winter). The SSW events are newlinemore frequent in the month of January and February in the year 1998-2009. Eight SSW newlineevents were selected during 17 years since 1992-2009. The vertical structure of SSW is newlinedemonstrated clearly in each warming events separately. Our observation reveals that the newlinedownward penetration of the disturbances in the stratosphere occurred with some delay with newlinerespect to upper stratosphere heights. newlineThe dynamical response of low latitude middle atmosphere to SSW is studied. It was newlinepresented using UKMO data for five major stratospheric warming events which show newlinecirculation changes at low latitudes due to these warming events and associated circulation newlinechanges at high latitude. All five winter periods considered here showed the intensification newlineof eastward winds in the mesosphere (above 1 hPa) and the presence of westward winds newlinecorresponding to major warming events occurred at high latitudes. The link between high newlineand low latitudes is due to the fact that the upward propagating planetary waves are newlineaccompanied by poleward heat flux which heats the high-latitude stratosphere and cools the newlinelow latitude counterpart. newline