Abstract. In the present study, we have used the Weather Research and Forecasting (WRF) model to simulate the features associated with a severe thunderstorm observed over Gadanki (13.5 • N, 79.2 • E), over southeast India, on 21 May 2008 and examined its sensitivity to four different microphysical (MP) schemes (Thompson, Lin, WSM6 and Morrison). We have used the WRF model with three nested domains with the innermost domain of 2 km grid spacing with explicit convection. The model was integrated for 36 h with the GFS initial conditions of 00:00 UTC, 21 May 2008. For validating simulated features of the thunderstorm, we have considered the vertical wind measurements made by the Indian MST radar installed at Gadanki, reflectivity profiles by the Doppler Weather Radar at Chennai, and automatic weather station data at Gadanki.There are major differences in the simulations of the thunderstorm among the MP schemes, in spite of using the same initial and boundary conditions and model configuration. First of all, all the four schemes simulated severe convection over Gadanki almost an hour before the observed storm. The DWR data suggested passage of two convective cores over Gadanki on 21 May, which was simulated by the model in all the four MP schemes. Comparatively, the Thompson scheme simulated the observed features of the updraft/downdraft cores reasonably well. However, all the four schemes underestimated strength and vertical extend of the updraft cores. The MP schemes also showed problems in simulating the downdrafts associated with the storm. While the Thompson scheme simulated surface rainfall distribution closer to observations, the other three schemes overestimated observed rainfall. However, all the four MP schemes simulated the surface wind variations associated with the thunderstorm reasonably well. The model simulated reflectivityCorrespondence to: M. Rajeevan (rajeevan@narl.gov.in) profiles were consistent with the observed reflectivity profile, showing two convective cores. These features are consistent with the simulated condensate profiles, which peaked around 5-6 km. As the results are dependent on initial conditions, in simulations with different initial conditions, different schemes may become closer to observations. The present study suggests not only large sensitivity but also variability of the microphysical schemes in the simulations of the thunderstorm. The study also emphasizes the need for a comprehensive observational campaign using multi-observational platforms to improve the parameterization of the cloud microphysics and land surface processes over the Indian region.

Abstract. Simultaneous observations of Indian

Abstract. Three campaigns are conducted with the Indian mesosphere-stratosphere-troposphere (MST) radar, located at Gadanki (13.5øN, 79.2øE), 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 ofhydrometeors 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 0øC 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 '• 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] The gamma parameters have been derived on the ground with the disdrometer and aloft with VHF and UHF radar measurements made at Gadanki in the southwest monsoon season. They have been used to study the variability of the shape-slope (m -L) relation with the climatic regime and also as a function of height. The m -L relation obtained at Gadanki differs from that derived at Florida and Oklahoma indicating climatic differences in the relation, which could be due to the microphysical differences in the rain DSD at these two locations. However, these differences could also arise due to the use of different type of disdrometers at these locations. For the first time, an attempt has been made to study the variation of this relation with height, and the analysis clearly reveals a significant variation in the coefficients of the relation with height. The vertical variability of the relation has been ascribed to the microphysical processes occurring in the height region concerned in the present study. These results suggest that for accurate retrieval of drop size distribution from polarimetric measurements and also for studies on the microphysics of rain systems, the vertical variability of the relation needs to be accounted, in particular in an environment where the DSD variations are considerable. In addition, the reduction of the scatter in the m -L plot after filtering light rain events, suggests that the m -L relation may be pertinent to moderate to heavy rain corroborating some of the earlier reports. Citation: Narayana Rao, T., N. V. P. Kirankumar, B. Radhakrishna, and D. Narayana Rao (2006), On the variability of the shape-slope parameter relations of the gamma raindrop size distribution model, Geophys. Res. Lett., 33, L22809,

The spatial and seasonal variability of the vertical structure of precipitation has been studied using 15 years of Tropical Rainfall Measuring Mission's Precipitation Radar (TRMM PR) version 7 data over India and adjoining oceans. Special emphasis has been put on six different climatic rain regimes and on different types of precipitation including the virga rain. The distribution of reflectivity factor (Z) above the freezing level height is broader in northwest India (NWI) and narrower over the Arabian Sea and west coast of India (ASWC) than in other selected regions, due to dominance of deep and shallow convective rain, respectively, in those regions. The height variation of contours in normalized distributions for Z indicates that evaporation of raindrops (low-level hydrometeor growth) could be significant in NWI (ASWC and Bay of Bengal). All the above features show clear seasonal variation and are observed predominantly during the southwest monsoon. The occurrence of virga rain clearly shows land-ocean contrast (less over the oceans) and seasonal variation (preponderant during premonsoon). Among different rain categories, the stratiform (convective) rain had highest (lowest) fraction of virga rain of >15-30% (<10%) over land regions. 1. The storm height (SH) vertical distributions show a peak in the vicinity of bright band (BB) in all regions, except for those regions and seasons, where convective precipitation is dominant. The well-defined BB feature and SH exhibit significant seasonal and regional variations, which are linked to variations in the occurrence of stratiform rain and height of BB. The spatial and seasonal variations of mean SH and the occurrence of deep and overshooting convective rain show good correspondence with the spatial variation of convective available potential energy.