Planetary waves in the mesosphere lower thermosphere during stratospheric sudden warming: observations using a network of meteor radars from high to equatorial latitudes

In the present communication, characteristics of mean winds and planetary waves in the mesosphere lower thermosphere (MLT) region during sudden stratospheric warming (SSW) events using observations from four meteor wind radars located at high, middle, low and equatorial latitudes are discussed. The response of the respective MLT regions to three SSW events that occurred during 2008-09, 2009-10 and 2011-12 winters are investigated. SSW signatures in the MLT zonal and meridional winds over the high latitude station Andenes (69.3 degrees N, 16.0 degrees E) are found to have significant differences from event to event. Mean wind reversals in the high latitude MLT are found to be preceding the corresponding signatures at 60 degrees N, 10 hPa by a few days. Zonal and meridional wind reversals extend to the MLT region over the mid latitude location Socorro (34.1 degrees N, 106.9 degrees W). However, MLT region over the low latitude station Thumba (8.5 degrees N, 77 degrees E) as well as the equatorial station Kototabang (0.2 degrees S, 100.3 degrees E) are found to be having a minimal response as far as mean winds are concerned. Apart from mean winds, planetary wave activity in the MLT region over the observational sites are examined, which show a systematic progression of planetary waves from high to equatorial latitudes during major as well as minor SSW events. To elucidate the origin of the observed planetary waves in the MLT region, the stratospheric winds are analyzed. Results suggest that the observed planetary waves have originated in the high-mid latitude middle atmospheric region. The present study provides observational evidence for secondary planetary wave generation in the high-mid latitude middle atmosphere and their equatorial propagation in the MLT as predicted by previous numerical modelling studies. Significance of the present study lies in employing a network of meteor radar observations to investigate the SSW signatures in the MLT region over high, middle, low and equatorial latitudes, simultaneously.