Vertical wave number spectra of wind fluctuations in the troposphere and lower stratosphere over Gadanki, a tropical station

Abstract

Spectral analyses of horizontal and vertical winds measured by Gadanki (13.5°N, 79.2°E) MST radar in the troposphere and lower stratosphere have been presented. Average slopes of the wave number spectra obtained in the power-law region are −2.5 for horizontal winds and −2.2 for vertical winds. Spectral indices are found to vary in different altitude zones with steepest slopes in the tropopause region for both horizontal and vertical winds. A seasonal variation of the slope has also been observed with higher value in summer. The ratio of the spectral magnitudes between the stratosphere and troposphere is found to be quite variable with an average value of 4.2 and 5.5 for horizontal and vertical winds, respectively. The power-law region seems to be dominated by gravity wave fluctuations and high correlations are observed between horizontal and vertical winds and between stratospheric and tropospheric energy densities. It is suggested that the saturated gravity wave model may be modified to match the observed spectral features. Spectral growth is found to be inhibited on some days which cannot be explained by gravity wave theory. It is felt that mesoscale spectra can be influenced by mechanism like 2D-turbulence.