Planetary wave activity in the Equatorial Mesosphere and Lower Thermosphere (MLT) during Anomalous QBO disruption in 2015-16

Quasi-Biennial Oscillation is an equatorial oscillation with downward descending eastward and westward wind regime of the average period of 28 months. The present work investigates the planetary wave activity in the equatorial Mesosphere Lower Thermosphere (MLT) during anomalous QBO phase change in November 2015- July 2016. The upward displacement of eastward winds developed at 20 hPa in late 2015 accompanied by the development of westward wind centered at 40 hPa. This 40 hPa westward wind reverted back to eastward in July 2016. Spectral analysis of Kotatobang (0.20 degrees S, 100.320 degrees E) Meteor radar winds between November 2015 and July 2016 indicates that the presence of long-period Kelin waves of periods 23days in the equatorial mesosphere during the Anomalous QBO event. The eastward propagating 23day wave is significantly observed in the mesospheric heights at the end of April 2016 and significant till July 2016. The presence of slow phase 23day wave at mesospheric altitudes motivated us to investigate the vertical propagation characteristics of these waves. Space-time Fourier analysis of ECMWF winds and OLR show the presence of 23 day period with zonal wavenumber 1, 2 and 3 indicating that tropical convection is the potential source for these waves and westward phase of stratospheric QBO winds during anomalous phase change during February to August 2016 might have favoured these waves to reach the mesosphere.