Abstract
Abstract. The turbulence refractivity structure constant (C2n ) is an important parameter of the atmosphere. VHF radars have been used extensively for the measurements of C2n. Presently, most of such observations are from mid and high latitudes and only very limited observations are available for equatorial and tropical latitudes. Indian MST radar is an excellent tool for making high-resolution measurements of atmospheric winds, associated shears and turbulence refractivity structure constant (C2n). This radar is located at Gadanki (13.45° N, 79.18° E), a tropical station in India. The objective of this paper is to bring out the height structure of C2n for different seasons using the long series of data (September 1995 – August 1999) from Indian MST radar. An attempt is also made to understand such changes in the height structure of C2n in relation to background atmospheric parameters such as horizontal winds and associated shears. The height structure of C2n, during the summer monsoon and post-monsoon season, shows specific height features that are found to be related to Tropical Easterly Jet (TEJ) winds. It is important to examine the nature of the radar back-scatterers and also to understand the causative mechanism of such scatterers. Aspect sensitivity of the received radar echo is examined for this purpose. It is observed that radar back-scatterers at the upper tropospheric and lower stratospheric heights are more anisotropic, with horizontal correlation length of 10–20 m, as compared to those observed at lower and middle tropospheric heights.Key words. Meteorology and atmospheric dynamics (climatology; tropical meteorology; turbulence)
Highlights
Study of the nature and characteristics of the atmospheric turbulence is of basic importance for understanding the atmospheric dynamics and coupling processes
MST radar is an excellent tool for making high-resolution measurements of atmospheric winds, associated vertical shears of horizontal winds and various atmospheric turbulence parameters
The following points can be noted: (a) The large year-to-year variability is noticeable in the height structure of C2n for all the months. (b) The band of minimum C2n between 10–16 km is broader in height range during winter and pre-monsoon months as compared to remaining months. (c) The secondary peak in C2n is distinctly visible in monsoon and post-monsoon months between 16–19 km
Summary
Study of the nature and characteristics of the atmospheric turbulence is of basic importance for understanding the atmospheric dynamics and coupling processes. MST radar is an excellent tool for making high-resolution measurements of atmospheric winds, associated vertical shears of horizontal winds and various atmospheric turbulence parameters. Most of such studies are confined to mid and high latitudes (VanZandt et al, 1978; Smith et al, 1983; Nastrom et al, 1986) and only a few measurements are available at low latitudes (Sato and Woodman, 1982; Tsuda et al, 1985; Jain et al, 1995; Narayana Rao et al, 1997). These observations have brought out specific features of height structure of C2n during the tropical monsoon season and the same are seen to be related to the easterly jet winds, near the tropopause, prevalent in the summer monsoon season
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