Abstract
Wind observations made at Gadanki (13.5°N) by using Indian MST Radar for few days in September, October, December 1995 and January, 1996 have been analyzed to study gravity wave activity in the troposphere and lower stratosphere. Horizontal wind variances have been computed for gravity waves of period (2-6) h from the power spectral density (PSD) spectrum. Exponential curves of the form eZ/H have been fitted by least squares technique to these variance values to obtain height variations of the irregular winds upto the height of about 15 km, where Z is the height in kilometers. The value of H, the scale height, as determined from curve fitting is found to be less than the theoretical value of scale height of neutral atmosphere in this region, implying that the waves are gaining energy during their passage in the troposphere. In other words, it indicates that the sources of gravity waves are present in the troposphere. The energy densities of gravity wave fluctuations have been computed. Polynomial fits to the observed values show that wave energy density increases in the troposphere, its source region, and then decreases in the lower stratosphere.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence; waves and tides)
Highlights
It is established that the momentum deposition by internal gravity waves in the middle and upper atmosphere provide signi®cant forcing to the meanow originally discussed by Hines (1960)
Chang et al (1997) used ST radar data from Christmas Island (1.95°N, 157.30°W) to study tropospheric gravity waves. They found a broad range of frequencies associated with gravity wave activity in the troposphere
Variance has been calculated by the normal procedure i.e. uH2 vH2 and is found to agree extremely well with the power spectral density (PSD) technique
Summary
It is established that the momentum deposition by internal gravity waves in the middle and upper atmosphere provide signi®cant forcing to the meanow originally discussed by Hines (1960). Chang et al (1997) used ST radar data from Christmas Island (1.95°N, 157.30°W) to study tropospheric gravity waves. In spite of signi®cant advancements, there have been very few studies of gravity wave activity in the tropical troposphere using radar observations. They found a broad range of frequencies associated with gravity wave activity in the troposphere. They applied two dierent cleaning algorithms ACR and SEP as explained in their paper and observed that small dierences in cleaned data sets can create large dierences in gravity wave variance and momentumux estimates in the lower atmosphere. This study presents an estimation of gravity wave intensity of periodicity between (2±6) h from radar data in the troposphere and lower stratosphere over a low latitude station, i.e. Gadanki (13.47°N, 79.18°E)
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