Statistical characteristics of the cloud cells in the categories of pre-convective, convective-initiation and convective-enhancement in the contrasting monsoon seasons over the rain-shadow region of peninsular India
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The cloud cells are categorized into six categories based on the radar reflectivity data obtained from Hyderabad S-band radar for the excess (2013) and deficient (2014) summer monsoon seasons. Among these, three categories (pre-convective, PC:19–27.5 dBZ, convective-initiation, CI: 28–36.5 dBZ and convective-enhancement, CE:37–45.5 dBZ) constitute about 59–64% of the total cloud population and play a vital role in the total rainfall. The monsoons are classified into excess/deficient if the seasonal rainfalls are more/less by 10% from the climatological mean. The study showed that on the daily scale, occurrence of these cells is ubiquitous feature of this rain-shadow region. Persistent formation of cells is due to large scale monsoon circulation and solar heating. On the intraseasonal scale monsoon conditions are classified into active/break conditions based on rainfall activity. Prevalence of high moisture (> 80%) and upward vertical velocity (up to 200 hPa) are responsible for high occurrence of cells in the active conditions. The solar heating is conducive for formation of cells in the break monsoon conditions and in the afternoon hours. Mean rate of transition from lower to higher level of convection intensity is − 0.72. The clouds in the states of PC, CI and CE show maximum/minimum values in the local afternoon/morning hours. The linkages established using multivariate regression analysis between VL category cells and the large-scale dynamic parameters and solar heating showed dominant role of these processes in the statistical prediction of number of these cells. The spatio-temporal variability of these cells will be useful for understanding the evolution of convection and modeling studies.
KeywordsConvection using radar Rain-shadow region Pre-convective Convective-initiation Convective-enhancement Dynamical processes Thermodynamical processes Bowen ratio
The authors wish to thank Director, IITM and Ministry of Earth Sciences (MoES). The authors gratefully acknowledge the ECMWF for providing the ERA Interim, Atmospheric model data, NCEP/NCAR for reanalysis data, Wyoming for upper air radiosonde data and IMD for providing high resolution gridded rainfall data used in this publication. Authors thank IMD, Hyderabad, Radar Team for providing the radar data for the summer monsoon seasons of 2013 and 2014. The authors are very thankful to the anonymous reviewers for the fruitful and constructive comments/suggestions which helped to improve the scientific level of the manuscript.
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