International Journal of Advances in Engineering & Technology, Mar. 2013. ©IJAET ISSN: 2231-1963 405 Vol. 6, Issue 1, pp. 405-414 A NEW ALGORITHM FOR CLASSIFICATION OF TROPICAL CONVECTIVE PRECIPITATING CLOUDS OVER NORTH- EASTERN REGION OF INDIA S. Balaji Kumar 1 , K. Krishna Reddy 1 , U. V. Murali Krishna 1 and H. G. Pathak2 1 Department of Physics, Yogi Vemana University, Kadapa-516003, A.P., India 2 Regional Meteorological Centre, India Meteorological Centre, Guwahati, Assam, India ABSTRACT The North East (NE) region of India is prone to severe thunderstorm during pre monsoon period. These pre- monsoon precipitations are measured at Guwahati (26 o 17’ N, 91 o 77’ E) using a laser based particle size and velocity (PARSIVEL) disdrometer from 15 April to 31 May 2010 under a national field campaign named Severe Thunderstorm Observational and Regional Modeling (STORM). For the improved understanding of these pre- monsoon thunderstorm a new cloud classification hybrid algorithm is developed based on thermodynamics and microphysical characterstics of precipitation. This algorithm can classify the premonsoon precipitaitng clouds into thuderstrom (TS), non- thuderstrom (NTS) and futher into convective & stratiform cloud fractions based on thermodynamic indices and rain integral parameters. The observation results showed that raindrops of Small and mid (large) size are having same concentration in convective (stratiform) regions of both TS and NTS precipitations. There is a large spread in the mean diameter (Dm) and total concentration (NT) at higher rainrate of TS than NTS. The coefficient (A) of the radar reflectivity and rainrate relation (Z-R) is found to be smaller for TS than NTS. There is a significant difference in Raindrop concentration in stratiform, convective regions of TS and NTS precipitation. K EYWORDS: Thunderstorm, Rainrate, Radar reflectivity, Raindrop Concentration. I. INTRODUCTION The Eastern and North Eastern (NE) part of India i.e., Gangetic West Bengal, Jharkhand, Orissa, Assam are affected by severe thunderstorms during pre-monsoon months, in particular, during April- May. These storms are also known as Norwesters as they move from Northwest to Southeast. Studies on thunderstorms at different parts of Indian are documented by a few researchers [1-4] using ground instruments, radisonde and satellite observations. There are studies on lightning [5], changes in thunderstorm electric field [6] and climatological aspects of thunderstorms, squalls [7] over Guwahati. There are different techniques viz., satellite [8 & 9], statistical [10], Fuzzy logic [11], Wavelet [12] and Neural Network [13] based approaches for classifying the precipitating clouds over the globe. However, so far there were no attempts on cloud classification over NE region of India. As microphysical characteristics are very important to understand thunderstorm development, propagation and dissipation, there is a need to study the Raindrop Size Distributions (RSD) parameters for the type of precipitation (stratiform, convective) and of thunderstorm, non thunderstorm [14-16]. Hence, for the first time an attempt is made to classify the precipitating clouds into stratiform, convective regions of Thunderstorm (TS) and Non-Thunderstorm (NTS) using a new hybrid algorithm. The main advantage of this algorithm is that, it utilizes both convective thermo- dynamical indices as well as RSD at the ground level. As convective indices gives information about the atmospheric instability of precipitating clouds and RSD represents the microphysical parameters of aloft cloud at the ground level, this hybrid algorithm is considered to be a more advantages for