Seasonal and interannual variations of gravity wave activity in the low-latitude mesosphere and lower thermosphere over Tirunelveli (8.7° N, 77.8° E)

Abstract

Abstract. The Mesosphere and Lower Thermosphere (MLT) winds acquired by medium frequency (MF) radar at Tirunelveli (8.7 • N, 77.8 • E) for the years 1993-2007 are used to study seasonal and interannual variabilities of gravity wave (GW) variances in the altitude region 84-94 km. The GW variances in zonal and meridional winds show semiannual oscillation with maximum variance during March-April and August-September and minimum during June-July and November-December months. The wind variances, in general, are observed to be enhanced during and after the year 1998 and they undergo large interannual variability, in particular, during spring equinox months. An enhancement of GW variances is observed during spring equinox months of the years 2000, 2004 and 2006. These larger GW enhancements, most of the times, coincide with eastward phase of zonally averaged stratospheric QBO at 30 hPa over equator and sudden stratospheric warming occurred at high latitudes. From the zonal and meridional variances, the perturbation ellipses are calculated and they show that the predominant direction of propagation of gravity waves is in SE-NW plane.

First results of warm mesospheric temperature over Gadanki (13.5°N, 79.2°E) during the sudden stratospheric warming of 2009

“…The eastward forcing due to breaking of gravity waves in the winter hemisphere induces an equatorward and upward flow at mesospheric altitudes leading to a temperature decrease of about 50 K at high latitudes. Sridharan and Sathishkumar (2008) noted increased gravity wave variance over Tirunelveli consistently during late winter of SSW years. The prevailing westward winds at stratospheric heights may have allowed eastward propagating gravity waves to reach mesospheric altitudes.…”

Dynamical response of low-latitude middle atmosphere to major sudden stratospheric warming events

“…Sridharan and Sathishkumar (2008) observed enhanced gravity wave variances in the altitude region 84-94 km over Tirunelveli during winters, when major SSW events occurred. Sathishkumar and Sridharan (2009) noted a decrease of planetary wave activity at MLT heights over Tirunelveli coinciding with larger gravity wave variances.…”

Lunar‐dependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings

“…[7] Low-latitude mesospheric and lower thermospheric effects associated with polar stratospheric warmings have been the subject of intense recent scientific interest [e.g., Vineeth et al, 2007;Sridharan and Sathishkumar, 2008].…”