Vertical propagation characteristics and seasonal variability of tidal wind oscillations in the MLT region over Trivandrum (8.5° N, 77° E): first results from SKiYMET Meteor Radar

Tidal activity in the Mesospheric Lower Thermosphere (MLT) region over Trivandrum (8.5° N, 77° E) is investigated using the observations from newly installed SKiYMET Meteor Radar. The seasonal variability and vertical propagation characteristics of atmospheric tides in the MLT region are addressed in the present communication. The observations revealed that the diurnal tide is more prominent than the semi/terdiurnal components over this latitude. It is also observed that the amplitudes of meridional components are stronger than that of zonal ones. The amplitude and phase structure shows the vertical propagation of diurnal tides with vertical wavelength of ~25 km. However, the vertical wavelength of the semidiurnal tide showed considerable variations. The vertical propagation characteristics of the terdiurnal tide showed some indications of their generating mechanisms. The observed features of tidal components are compared with Global Scale Wave Model (GSWM02) values and they showed a similar amplitude and phase structure for diurnal tides. Month-to-month variations in the tidal amplitudes have shown significant seasonal variation. The observed seasonal variation is discussed in light of the variation in tidal forcing and dissipation

Seasonal variation of gravity waves in the Equatorial Middle Atmosphere: results from ISRO's Middle Atmospheric Dynamics (MIDAS) program

Altitude profiles of temperature in the stratospheric and mesopheric region from lidar observations at NARL, Gadanki, India, during December 2002–April 2005, as part of ISRO's Middle Atmospheric Dynamics – "MIDAS (2002–2005)" program are used to study the characteristics of gravity waves and their seasonal variation. Month-to-month variation of the gravity wave activity observed during the period of December 2002–April 2005 show maximum wave activity, with primary peaks in May 2003, August 2004 and March 2005 and secondary peaks in February 2003 and November 2004. This month-to-month variation in gravity wave activity is linked to the variation in the strength of the sources, viz. convection and wind shear, down below at the tropospheric region, estimated from MST radar measurements at the same location. Horizontal wind shear is found to be mostly correlated with wave activity than convection, and sometimes both sources are found to contribute towards the wave activity

Gravity wave flux retrievals using meteor radars

The ability of all-sky interferometric meteor radars to measure mean wind and high-frequency gravity wave wind perturbations from meteor radial velocities is assessed. A Monte-Carlo technique that models line-of-sight meteor wind measurements with realistic errors in angle-of-arrival and range is used to investigate uncertainties in mean wind and gravity wave wind parameters as a function of meteor echo rate. It is shown that mean horizontal wind speeds are recovered with reasonable accuracy at meteor rates as low as 10 hr-1. Mean-square horizontal wind perturbation can be derived with relatively little averaging, but u′u′ momentum fluxes are recovered with much less accuracy, which means that considerable averaging is required to produce meaningful values. Results are illustrated using meteor wind radar observations taken over a 30-day period in January-February 2006 in Northern Australia. © 2010 by the American Geophysical Union.R. A. Vincent, S. Kovalam, I. M. Reid and J. P. Younge