International Journal of Earth and Atmospheric Science | July-September, 2015 | Vol 2 | Issue 3 | Pages 71-79 © 2015 Jakraya Publications (P) Ltd INTERNATIONAL JOURNAL OF EARTH AND ATMOSPHERIC SCIENCE Journal homepage: www.jakraya.com/journal/ijeas ORIGINAL ARTICLE Seasonal and Diurnal Variation of Mesoscale Convective Systems Over Southern Peninsular India as Observed by TRMM Satellite Anal Chandra Sarma 1* , Atri Deshamukhya 2 and Sanjay Sharma 3 1 Department of Physics, Patkai Christian College, Dimapur, India. 2 Department of Physics, Assam University, Silchar, India. 3 Department of Physics, Kohima Science College, Kohima, India. *Corresponding Author: Anal Chandra Sarma Email: anal_sarma@yahoo.co.in Submitted: 22/04/2015 Revised: 29/08/2015 Accepted: 30/08/2015 Abstract Mesoscale Convective Systems (MCSs) contribute a large proportion of the earth’s precipitation and hence their study is important from climatological point of view. In this paper, seasonal and diurnal variation of MCSs parameters over southern peninsular India has been studied. MCSs data over land for a period of 13 years (1998-2010) from Precipitation Measuring Mission (PMM) website of Utah University (www.trmm.chpc.utah.edu) have been utilized for this study. Distinct seasonal and diurnal variation of MCS parameters are observed over the study region. Number of occurrence and rainfall are maximum in June over southwest peninsular India and in October over southeast peninsular India. MCSs are found to be more severe during pre-monsoon and least severe during south-west monsoon. Their severity is found to be maximum in the month of May by virtue of highest median value of 20dBZ echo-top height (14.8 km) associated with highest median value of CAPE (1323 J/Kg). Convective fraction of rainfall is maximum in April and minimum in December. MCSs occurrence is found to be maximum in the late afternoon to evening and minimum in morning. They are found to be more intense during midday (10-14 hrs) and least intense during midnight (22-02 hrs). Diurnal cycle of convective fraction shows midday maximum and late night minimum. Key words: Mesoscale Convective System, TRMM, Seasonal and Diurnal, Echo-Top Height, CAPE. 1. Introduction Mesoscale Convective Systems (MCSs) are defined as “cloud systems that occur with an ensemble of thunderstorms and produces a contiguous precipitation area, with at least ~100 km or more in horizontal scale in one direction (Houze, 1982)”. The overall cloud and precipitation pattern of MCSs may be round or linear and include weather system such as tropical cyclones, mesoscale convective complexes, squall lines among others. Majority of the MCSs are linear in shape as indicated by their eccentricity (Augustine et al., 1989; Morel and Senesi, 2002; Sharma et al., 2009). Mesoscale convective complexes (MCCs) are circular (eccentricity >0.7), but majority of the MCSs do not meet the MCCs criteria (Augustine et al., 1989; Morel and Senesi, 2002). MCSs evolve over 3 to 6 hours and at some stage contain both convective and stratiform precipitation regions contributing a large proportion of the earth’s precipitation (Houze, 1993). Across the tropics, stratiform precipitation accounts for 40% of the total rainfall, while it covers 73% of total raining area (Schumacher and Houze, 2003). They appear in many forms, ranging from a relatively disorganized mass of convective cells to a highly organized convective line and produce a large variety of hazardous weather (Fujita, 1978; Sharma et al., 2009). The study of MCS by remote sensing is carried out in many spectral band such as visible, infrared and microwave, but the advantage of using microwave is that it penetrates through clouds and facilitates the study of internal structures of precipitating systems (Sharma et al., 2009). In order to study tropical rainfall by facilitating remote sensing of MCS, the Tropical Rainfall Measuring Mission (TRMM) satellite which consists of precipitation radar (TRMM-PR) and microwave imager (TMI) was launched in 1997 (Kummerow et al., 1998). Microwave sensors of