Turbulence characteristics in the tropical mesosphere as obtained by MST radar at Gadanki ( 13 . 5 ◦ N , 79 . 2 ◦ E )

Turbulent kinetic energy dissipation rates (ε) and eddy diffusion coefficients (K z) in the tropical mesosphere over Gadanki (13.5 • N, 79.2 • E), estimated from Doppler widths of MST radar echoes (vertical beam), observed over a 3-year period, show a seasonal variation with a dominant summer maximum. The observed seasonal variation of ε and K z in the mesosphere is only partially consistent with that of gravity wave activity inferred from mesospheric winds and temperatures measured by rockets for a period of 9 years at Trivandrum (8.5 • N, 77 • E) (which shows two equinox and one summer maxima) lying close to Gadanki. The summer maximum of mesospheric ε and K z values appears to be related to the enhanced gravity wave activity over the low-latitude Indian subcontinent during the southwest monsoon period (June – September). Both ε and K z in the mesosphere over Gadanki show an increase with an increase in height during all seasons. The absolute values of observed ε and K z in the mesosphere (above ∼80 km) does not show significant differences from those reported for high latitudes. Comparison of observed K z values during the winter above Gadanki with those over Arecibo (18.5 • N, 66 • W) shows that they are not significantly different from each other above the ∼80 km altitude.