Tropical precipitating systems observed with Indian MST radar

Three campaigns are conducted with the Indian mesosphere-stratosphere-troposphere (MST) radar, located at Gadanki (13.5°N, 79.2°E), India, to study the precipitating systems in the tropics. This study mainly deals with (1) classification of precipitating clouds and the spectral characteristics of echoes associated with these cloud systems and (2) characteristics of the radar bright band. The radar gets echoes scattered both from refractive index fluctuations and precipitation particles in moderate to heavy precipitation conditions. These echoes are separated in the spectral domain to determine the vertical air motion and the Doppler velocity of hydrometeors simultaneously. The tropical precipitating systems are classified as stratiform and convective using the reflectivity and vertical velocity distribution. The echo power, spectral width, and vertical velocities of the ambient air and hydrometeors in both the cloud systems have been compared. Aspect sensitivity of the echoes from the hydrometeors and refractive index fluctuations in both stratiform and convective atmosphere is studied. A transition stage, where the stratiform precipitation is associated with the convection, is also reported. Backscattered power from precipitation particles is used to estimate the reflectivity factor (dBZ), and these values along with spectral width and vertical velocity values are used to identify the bright band structure. The reflectivity at the bright band, up to 42 dBZ, is found to be 10–12 dB more than the average value of reflectivity below the bright band. Discussion on the factors contributing to this enhancement is also included. A clear layered structure around the 0°C isotherm in the reflectivity profile of the precipitation echo confirms the presence of the bright band. The thickness of the bright band is estimated and is correlated with the peak reflectivity at the bright band. Comparison of the average terminal velocity of hydrometeors with their average Doppler velocities below the bright band shows the presence of gentle updrafts of a few cm s−1 in stratiform precipitation. These studies are made for the first time with the Indian MST radar and also demonstrate the capability of a VHF radar in studying precipitating systems in addition to the turbulence to which these radars are highly sensitive.

[1]  D. A. Carter,et al.  Interactions between clear‐air reflective layers and rain observed with a boundary layer wind profiler , 1995 .

[2]  Warner L. Ecklund,et al.  Classification of Precipitating Clouds in the Tropics Using 915-MHz Wind Profilers , 1995 .

[3]  C. Liu,et al.  The investigations of the atmospheric precipitations by using Chung-Li VHF radar , 1991 .

[4]  Y. Chu,et al.  Observations of precipitation associated with a cold front using a VHF wind profiler and a ground‐based optical rain gauge , 1998 .

[5]  Susumu Kato,et al.  A Direct Method for Deriving Drop-Size Distribution and Vertical Air Velocities from VHF Doppler Radar Spectra , 1986 .

[6]  F. M. Ralph,et al.  Using Spectral Moment Data from NOAA's 404-MHz Radar Wind Profilers to Observe Precipitation , 1995 .

[7]  J. Marshall,et al.  THE DISTRIBUTION OF RAINDROPS WITH SIZE , 1948 .

[8]  R. C. Srivastava,et al.  Doppler radar characteristics of precipitation at vertical incidence , 1973 .

[9]  K. Wakasugi,et al.  Further Discussion on Deriving Drop-Size Distribution and Vertical Air Velocities Directly from VHF Doppler Radar Spectra , 1987 .

[10]  Chunze Lin,et al.  The severe depletion of turbulent echo power in precipitation observed using the Chung‐Li VHF Doppler radar , 1994 .

[11]  K. Reddy,et al.  Studies on refractivity structure constant, eddy dissipation rate, and momentum flux at a tropical latitude , 1997 .

[12]  R. Vincent,et al.  A General Approach to the Retrieval of Raindrop Size Distributions from Wind Profiler Doppler Spectra: Modeling Results , 1993 .

[13]  Hisato Iwai,et al.  Computer processing for deriving drop-size distributions and vertical air velocities from VHF Doppler radar spectra , 1990 .

[14]  I. Hirota,et al.  Direct measurement of air and precipitation particle motion by very high frequency Doppler radar , 1985, Nature.

[15]  Earl E. Gossard,et al.  Measurement of Cloud Droplet Size Spectra by Doppler Radar , 1994 .

[16]  Robert A. Houze,et al.  Melting and Evaporation of Hydrometeors in Precipitation from the Anvil Clouds of Deep Tropical Convection , 1979 .

[17]  J. R. Probert-Jones,et al.  The radar equation in meteorology , 1962 .

[18]  P. Balamuralidhar,et al.  Indian MST radar 1. System description and sample vector wind measurements in ST mode , 1995 .

[19]  A. Bemis,et al.  A QUANTITATIVE STUDY OF THE “BRIGHT BAND” IN RADAR PRECIPITATION ECHOES , 1950 .

[20]  Frédéric Fabry,et al.  Long-Term Radar Observations of the Melting Layer of Precipitation and Their Interpretation , 1995 .

[21]  R. Houze.  Stratiform precipitation in regions of convection : A meteorological paradox ? , 1997 .

[22]  S. Avery,et al.  Combined use of 50 MHz and 915 MHz wind profilers in the estimation of raindrop size distributions , 1992 .

[23]  Warner L. Ecklund,et al.  Tropical precipitation studies using a 915‐MHz wind profiler , 1995 .

[24]  Y. Chu,et al.  An examination of the wind‐driven effect on the drift of precipitation particles using the Chung‐Li VHF radar , 1997 .