Abstract
Abstract. The potential utility of Mesosphere-Stratosphere-Troposphere (MST) radar measurements of zonal, meridional and vertical winds for divulging the gravity wave vertical wave number spectra is discussed. The data collected during the years 1995–2004 are used to obtain the mean vertical wave number spectra of gravity wave kinetic energy in the tropical troposphere over Gadanki (13.5° N, 79.2° E). First, the climatology of 3-dimensional wind components is developed using ten years of radar observations, for the first time, over this latitude. This climatology brought out the salient features of background tropospheric winds over Gadanki. Further, using the second order polynomial fit as background, the day-to-day wind anomalies are estimated. These wind anomalies in the 4–14 km height regions are used to estimate the profiles of zonal, meridional and vertical kinetic energy per unit mass, which are then used to estimate the height profile of total kinetic energy. Finally, the height profiles of total kinetic energy are subjected to Fourier analysis to obtain the monthly mean vertical wave number spectra of gravity wave kinetic energy. The monthly mean vertical wave number spectra are then compared with a saturation spectrum predicted by gravity wave saturation theory. A slope of 5/3 is used for the model gravity wave spectrum estimation. In general, the agreement is good during all the months. However, it is noticed that the model spectrum overestimates the PSD at lower vertical wave numbers and underestimates it at higher vertical wave numbers, which is consistently observed during all the months. The observed discrepancies are attributed to the differences in the slopes of theoretical and observed gravity wave spectra. The slopes of the observed vertical wave number spectra are estimated and compared with the model spectrum slope, which are in good agreement. The estimated slopes of the observed monthly vertical wave number spectra are in the range of −2 to −2.8. The significance of the present study lies in using the ten years of data to estimate the monthly mean vertical wave number spectra of gravity waves, which will find their application in representing the realistic gravity wave characteristics in atmospheric models.
Highlights
Studies of the atmospheric gravity waves are cynosures for many atmospheric researchers, as they play a major role in a variety of phenomena taking place right from the planetary boundary layer to the upper atmosphere. Hines (1960) was the first to propose a theory, interpreting the observed atmospheric fluctuations as manifestations of the upward propagating internal gravity waves
Using the ten years of Indian MST radar observations, a climatology of zonal, meridional and vertical winds is developed and the same is shown in Fig. 2a, b and c, respectively
It is very interesting to observe the features of the Tropical Easterly Jet (TEJ) in the upper tropospheric region (13– 17 km), which is a well-established gravity wave source apart from atmospheric convection and orography over the present observational site
Summary
Studies of the atmospheric gravity waves are cynosures for many atmospheric researchers, as they play a major role in a variety of phenomena taking place right from the planetary boundary layer to the upper atmosphere. Hines (1960) was the first to propose a theory, interpreting the observed atmospheric fluctuations as manifestations of the upward propagating internal gravity waves. Hines (1960) was the first to propose a theory, interpreting the observed atmospheric fluctuations as manifestations of the upward propagating internal gravity waves. This theory has since been universally accepted and has provided a firm foundation for subsequent gravity wave studies. Since a considerable amount of effort is being focused towards the exploration of gravity waves Most of these studies identified frontal systems, orography, jet streams and convective systems as major sources for the gravity waves. Since the convective phenomena is dominant in the tropical region, it is of considerable significance to study gravity wave activity over tropics
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