Indian MST radar 2. First scientific results in ST mode

Abstract

Clear air radars operating in the VHF range provide excellent information on middle atmospheric structure and dynamics with fine height and time resolutions. One such radar is installed at Gadanki, a tropical station in India. Experiments were carried out using the ST mode of this newly established MST radar to study the atmospheric wind field, characteristics of atmospheric stable layers, and clear air turbulence over this tropical station. Atmospheric stable layers are observed at various heights in the troposphere and lower stratosphere. Multilayer structures are observed near the tropopause and in the lower stratosphere. The range‐time‐intensity (RTI) maps for the zenith beam show that once these structures are formed, they are seen to last for more than an hour, indicating their large horizontal extent. The model computations of radar signal‐to‐noise ratio (SNR) for zenith beam, using simultaneous radiosonde observations taken at Madras, show a gross agreement with the observed SNR. However, the model SNR profiles do not show the fine structure observed by the radar, the limitation of the model profiles being the lower height resolution of the radiosonde measurements. The refractivity turbulence structure constant C2n is determined using SNR for 20° off‐zenith beams pointed in east, west, north, and south directions. Profiles of C2n for the four oblique beams are found to agree within 10 dB, indicating that the intensity of the turbulence for the same range bin, within the volume scanned by the radar, is the same. The parameter C2n is also computed using meteorological parameters and compared with radar C2n. The observed and model C2n profiles are found to agree within 5 dB. Radar C2n profiles are found to show large diurnal and day‐to‐day variability. The results of an experiment conducted to determine the effect of transmitted pulse length on the received signal spectral width show that the wind shear effect is important for oblique beams and for longer pulse lengths, where as the beam‐broadening effect is important for both oblique and vertical beams for all pulse lengths. Various turbulence parameters are determined using the observed spectral width after correcting for these effects.

Diurnal and seasonal variability of TKE dissipation rate in the ABL over a tropical station using UHF wind profiler

“…It is, therefore, necessary to choose clear air days for estimating the turbulence parameters from the UHF radar observations. Spectral width, obtained from the radar Doppler spectrum, has been extensively used in many studies on turbulence (e.g., Frisch and Clifford, 1974;Sato and Woodman, 1982;Doviak and Zrnic, 1984;Hocking, 1983Hocking, , 1985Fukao et al, 1994;Jain et al, 1995;Nastrom and Eaton, 1997;Narayana Rao et al, 1997;Hermawan and Tsuda, 1999;White et al, 1999;Furumoto and Tsuda, 2001;Sandra Jocoby-Koaly et al, 2002).…”

VHF radar observation of atmospheric winds, associated shears and <b>C<sup>2</sup></b><b><sub>n</sub></b> at a tropical location: interdependence and seasonal pattern

“…Therefore, more measurements are necessary to have a better idea of C 2 n in this region. Jain et al (1995) presented first measurements of C 2 n in the height range of 4-11 km using Indian MST radar in ST mode with a peak power aperture product of 4.8 × 10 6 Wm 2 . Narayana have presented measurements of C 2 n made using Indian MST radar in MST mode with an average power aperture product of 3 × 10 10 Wm 2 .…”

“…However, most of such studies are confined to mid and high latitudes 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). The received radar echo intensity is generally used for determination of the parameter refractivity structure constant (C 2 n ).…”

UHF wind profiler observations of monsoon low-level jet (MLLJ) and its association with rainfall over a tropical Indian station

“…UHF/VHF Wind profiler radars have proven to be excellent tools to study atmospheric winds, associated vertical shears of horizontal winds and various atmospheric turbulence parameters. Several studies are confined to mid and high latitudes (e.g., VanZandt et al, 1978;Smith et al, 1983;Nastrom et al, 1986) and some observational studies are available at low latitudes (e.g., Sato and Woodman, 1982;Tsuda et al, 1985;Jain et al, 1995;Rao et al, 1997).…”