Some characteristics of low pressure systems and summer monsoon rainfall over Orissa

Abstract

The present study was undertaken to find out characteristic features like frequency, intensity, movement, region of formation, days of occurrence, etc. of synoptic disturbances such as low, depression, cyclonic storm, etc. forming over Orissa and neighbouring sea and land regions during summer monsoon season (June- September). The study is based on the data of 20 years (1980-1999). The principal objective of this study was to understand the contribution of the low pressure systems (LPS) including low, depression and cyclonic storm to interannual variability of summer monsoon rainfall over Orissa. Most of the LPS develop over northwest (NW) Bay of Bengal and move towards east Madhya Pradesh across Gangetic West Bangal (GWB) during June, July and across Orissa during August and September. The rainfall over Orissa is more related with the frequency of LPS days over Orissa and adjoining land/sea regions than with the frequencies of LPS, cyclonic disturbances (CD) and CD days over those regions. The seasonal monsoon rainfall over Orissa is significantly higher with higher frequency of LPS days over NW Bay and Orissa. It is less with higher frequency of LPS days over Jharkhand followed by west central Bay off north coastal Andhra Pradesh and Bangladesh. The frequencies of monsoon low days are higher over NW Bay and Orissa thus compensating the adverse impact of reduced CD and CD days on rainfall over Orissa in recent years. The monthly and seasonal monsoon rainfall over Orissa show no significant trends in recent years. It may be due to insignificant trends in those LPS days which are significantly correlated with rainfall over Orissa.