Meteor radar observations of short-term variability of quasi 2 day waves and their interaction with tides and planetary waves in the mesosphere-lower thermosphere region over Thumba (8.5°N, 77°E)

Meteor radar measurements of zonal and meridional winds over a low-latitude station, Thumba (8.5 degrees N, 77 degrees E), during March 2006 to March 2009 are used to study the quasi 2 day wave structure in the mesosphere-lower thermosphere (MLT) region. Emphasis is placed on the study of the day-to-day variations of quasi 2 day waves and their interaction with diurnal tides and planetary waves. The seasonal variation of quasi 2 day waves showed two maxima, one during summer and the other during winter, coinciding with the strong eastward winds in the MLT region along with a distinct peak during the month of October. Subsequent analysis of TIMED/SABER observations during October revealed the presence of a westward propagating quasi 2 day wave with zonal wave number 3 over the present latitude. The seasonal variation of quasi 2 day wave is also discussed with respect to the Stratospheric Semiannual Oscillation (SSAO), and we found that the quasi 2 day wave activity peaks in the MLT region during the phase transition of SSAO as well as during the eastward phase. Wavelet and subsequent bispectral analysis confirmed the wave-wave interactions of quasi 2 day wave and planetary waves with periods of 5-10 and 15-20 days. The 16 h oscillation, which is believed to be generated by interaction of quasi 2 day wave and diurnal tide, showed an excellent correlation with quasi 2 day wave activity. Apart from reporting day-to-day variation of quasi 2 day wave for the first time over this latitude, there are two new results from the present study: (1) a consistent peak in quasi 2 day activity during October, which has never been reported and has been observed for the first time over low latitudes, and (2) the relation between SSAO and quasi 2 day wave activity.