Regional variation of mesoscale precipitation system during premonsoon period in Bangladesh

Abstract

Regional variation of mesoscale precipitation systems is analyzed in and around Bangladesh using six-year (2000-2005) radar data obtained from the Bangladesh Meteorological Department (BMD). Over the study period, regional analysis revealed that the arc, line and scattered types precipitation systems were dominant in the northwest and northeast quadrant during the pre-monsoon period. In monsoon, the arc and line types precipitation systems are dominant in the northwest quadrant and scattered type precipitation systems is dominant in the southeast quadrant. Total 230 arc type precipitation systems are indentified during the study period and classified into symmetric type precipitation systems (STPS), asymmetric type precipitation systems (ATPS), combination of symmetric and asymmetric type precipitation systems (CSATPS) and unclassified type precipitation systems (UTPS). During the analysis period, the occurrence frequency of STPS, ATPS, CSATPS and UTPS is 23%, 43%, 21% and 13%, respectively. Seasonal analysis showed that ATPS and STPS is dominated in the pre-monsoon and monsoon period, respectively. Regional analysis of different arc type systems indicate that at the mature stage of their life cycle, STPS, ATPS, and CSATPS is dominated in southwest (northwest), northeast (southeast) and northwest (northwest) quadrants during pre-monsoon (monsoon) period. The maximum occurrence frequency of UTPS is found in the northeast and southwest quadrant during pre-monsoon and in the southwest quadrant during the monsoon season. The statistical analysis of diurnal variation of precipitation systems showed double peaks: primary peak at 03-06 LST (morning) and secondary maximum at 12-15 LST (afternoon). In addition, case study showed that the quantitative comparison between BMD radar retrieve rainfall and conventional raingauge rainfall is not possible.