[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,

Raindrop size distribution (DSD) parameters are retrieved from dual-frequency (UHF and VHF) wind profiler measurements made at Gadanki, India, in a summer monsoon season. The convoluted UHF spectra are first corrected for vertical air motion and spectral broadening (using VHF measurements) and later are used for deriving DSD parameters. Two distinctly different case studies, a mesoscale convective system and a pure stratiform precipitation system, have been considered for a detailed study. DSD parameters obtained in these case studies reveal systematic variations of DSD from case to case and also from one rain regime to another within the same precipitating system. A statistical study has been carried out using the profiler data collected during the passage of 16 rain events. The retrieved DSD profiles are divided into separate rain regimes (stratiform and convection), based on reflectivity, to examine salient microphysical characteristics and the vertical variability of DSD in different precipitation regimes. The distribution of DSD parameters is, in general, wider in the convective rain regime than in the stratiform regime, particularly below 2.4 km. The vertical variation of the gamma parameter distribution in the stratiform rain regime is minimal, indicating that the microphysical processes (growth and decay), which alter the rain DSD, may be in equilibrium. On the other hand, the distribution in the convective rain regime appears to be more complex, with the mean profile of the shape parameter varying significantly with height. The observed vertical variability of the gamma parameters and the median volume diameter in the convective rain regime is attributed to two major microphysical processes: evaporation and breakup. The role of other processes, like drop sorting and collision–coalescence, in altering the DSD parameters is also discussed. The present statistics, representing continental monsoon rainfall, are compared with the existing statistics at Darwin, Australia, and the results are discussed in light of DSD differences in oceanic and continental monsoon precipitation.

The lower atmospheric wind profiler (LAWP) measurements made at Gadanki, India, have been used to develop an objective algorithm to classify the tropical precipitating systems. A detailed investigation on the existing classification scheme reveals major shortcomings in the scheme. In the present study, it is shown with examples that the Doppler velocity gradient (DVG) criterion is a necessary but certainly not a sufficient condition to identify the radar bright band. Such gradients in Doppler velocity can exist in other types of rain systems, for example, in convection, due to the modulation of Doppler velocity of hydrometeors by vertical air motion. The approach of the new classification scheme deviates considerably from that of existing algorithms. For instance, the new algorithm, in contrast to identifying the stratiform rain and assuming the remaining rain as convection, identifies first convection and later stratiform precipitation based on their specific characteristics. The other interesting feature in this algorithm is that it was built on the strengths of other potential classification schemes and theoretically accepted thresholds for classification of the precipitation. The performance of the new algorithm has been verified with the help of time-height maps of profiler moments and corresponding surface rainfall patterns.

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