Seasonal variability in mean sea level pressure extremes over the Indian region

The extreme values of maximum and minimum daily atmospheric mean sea level pressure (MSLP) and its seasonal variability over the 11 zones of India, Arabian Sea, Bay of Bengal and all-India as a whole during the period 1951–2007 using daily-averaged NCEP/NCAR reanalysis dataset have been analyzed. Trends in the frequencies of low MSLP days are found to be decreasing and for high MSLP days are increasing during winter, pre-monsoon, summer monsoon and post-monsoon seasons. Decrease in the extreme low MSLP days observed in the study may affect the seasonal rainfall distribution and its characteristics across India. High MSLP days are found to be negatively correlated with the All-India Summer Monsoon Rainfall (AISMR). Both the extreme frequencies of the MSLP days show a different nature in the recent decades. The high MSLP days shows a sharp increasing tendency after 1975 with a large variability whereas least variability was observed in case of the low MSLP days. Low/high MSLP days are found to be negatively/positively correlated with Nino4 SSTs for all the seasons. The possible causes for the large-scale changes in the characteristics and its seasonal variabilities of extreme low/high MSLP days might be the increased frequency of strong El Niño events during the period 1975–2007. This might have triggered the Indian summer monsoon circulation causing the reduction in the low MSLP days that resulted in decreasing tendency of the rainfall activities across India.