Changes in the frequencies of northeast monsoon rainy days in the global warming

The frequencies of the days having different rainfall limits in northeast monsoon season over South Peninsular [SP] India comprising of five meteorological subdivisions are evaluated using the grid-point rainfall data of India Meteorological Department [IMD] for the period 1951-2008. The study period is divided into two parts 1951-1969 [pre-global warming period] and 1970-2008 [global warming period] as the Earth shows a perceptible rise in the temperature from the beginning of 1970s. The differences in the frequencies of the days having different rainfall limits [zero, 0 to 20 mm, 20-60 mm, 60-100 mm and greater than 100 mm] for these two periods are also evaluated. Further, the differences in the mean rainfall amounts over SP India and zonal wind at 850 hPa for the domain 74 degrees E-85 degrees E, 8 degrees N-20 degrees N in northeast monsoon season using NCEP-NCAR reanalysis data sets for these two periods are calculated and tested with the Z-statistic. It is observed that there is an enhancement in the northeast monsoon rainfall over the major area of SP India in the global warming period which is associated with the intensification of easterly wind belt in the lower troposphere over the major part of northeast monsoon region, decrease in the frequency of no rainfall days and increasing tendencies in the frequencies of the days having all the limits of rainfall except for 2060 mm limit. (C) 2012 Elsevier B.V. All rights reserved.