Impact of convection over the equatorial trough on summer monsoon activity over India

Abstract

The cause for the disruption of rainfall (break in monsoon conditions) over the Indian subcontinent during the monsoon months, for the period, 1979 - 1998, are investigated using the pentad rainfall data from the Global Precipitation Climatology Project (GPCP). Most (about 73%) of the break in monsoon (BM) events were associated with the convective activity (rainfall more than 30 mm/pentad) over the equatorial trough (ET) region. The association between these events and the convective activity over the western (WET) and eastern equatorial trough (EET) regions of the tropical Indian Ocean were further explored. These relationships were tested for different (deficit, normal and excess) monsoon conditions over the Indian subcontinent and the El Nino conditions in the Pacific Ocean. There appears to be a negative and significant correlation between the Central Indian Region (CIR) rainfall and EET during deficit and non El Nino years. During deficit and El Nino years, the CIR rainfall exhibited a negative correlation with WET. In the case of years with no breaks, the EET was negatively (positively) correlated during the years 1982 & 1992 (1994 & 1997) with the all India rainfall (AIR). The convective activity was more intense over the EET than WET during prolonged BM and also in a deficit and non El Nino year (1979). The probabilities of occurrence of no BM conditions are more in the El Nino years. The number of lows and depressions, in general, were also more in the years when there were no BM events.