Propagation of short period (10-40 min) atmospheric gravity waves from troposphere to mesosphere over Gadanki, India

The Indian MST radar at Gadanki (13.5°N, 79.2°E) has been utilised to conduct a detailed study of the close coupling between the troposphere and the mesosphere through the vertically propagating atmospheric gravity waves. For this purpose two cases from a special campaign dedicated to the simultaneous measurement of the fluctuations in the UTLS (Upper Troposphere and Lower Stratosphere) and in the mesosphere during 2001 and one case from a follow up observation in 2002 have been investigated. By using both the FFT and wavelet techniques, the near simultaneous tropospheric and mesospheric data of radar return signal strengths and tropospheric wind fields are analysed. The signatures of relatively high frequency gravity waves with periods between ~10 and 40 min have been clearly traced as propagating waves from the tropospheric turbulent layer heights (~8–18 km) to the lower mesospheric heights (65–80 km). Significant peak correlation coefficients of 0.56 and 0.45 have been found between the SNR time series of pairs of troposphere and mesosphere levels indicating the propagation of high speed gravity waves. The time series of wavelet spectra determined for the tropospheric SNR/zonal winds and the mesospheric SNR show that the detectability of the gravity waves increases at mesospheric heights. It is shown that the continuous SNR values received from the mesosphere can be used as an effective parameter for studies featuring mesospheric wave dynamics. Based on the observed values of vertical wavelengths and wave amplitudes, the horizontal wavelengths, wave phase and group velocities have been estimated for different wave periods. These results have implications on monitoring of the ubiquitous atmospheric gravity waves generated mainly by the tropospheric weather system of the tropical region from their imprint on the mesospheric turbulence structures.