Abstract. 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.

Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; tropical meteorology; wave and tides)