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

Abstract

Causes of disruption of rainfall (break in monsoon conditions) over the Indian subcontinent during the monsoon months for the period 1979–1998 are investigated using pentad rainfall data from the Global Precipitation Climatology Project (GPCP). Most (about 73%) of the break in monsoon (BM) events were associated with 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 Niño 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 Niño years. During deficit and El Niño years (1982 and 1987), both CIR and all India rainfall (AIR) exhibited a negative correlation with WET. In the case of years with no breaks, EET was negatively (positively) correlated during the years 1982 and 1992 (1994 and 1997) with AIR. The convective activity was more intense over EET than WET during prolonged BM and also in a deficit and non‐El Niño year (1979).

Acknowledgements

The authors are grateful to the Global Precipitation Climatology Project of the World Data Center for Meteorology, Asheville, USA for providing the GPCP data. The rainfall data for the present study was obtained from the Indian Institute of Tropical Meteorology. The authors would also like to thank two anonymous reviewers for their critical comments that helped vastly in improving an earlier version of the manuscript and making the ideas clearer. Freeware Ferret was used for the analysis. Two of the authors (M.R.R.K and S.S.C.S) would like to thank the DST for financial support.