Abstract

Being an agricultural country, the success or failure of the crops over India is always viewed with the greatest concern and these problems are closely linked with the behavior of the summer monsoon rains from June to September (JJAS) as it contributes more than 80% of the annual total rainfall. India has experienced severe drought conditions in the past including recently in 2002 and 2004 with seasonal rainfall departures of -19% and -13% respectively. The present study is an attempt to explore simultaneous as well as a predictive relationship between Indian Summer Monsoon Rainfall (ISMR) and the convective activity over the Indo-Pacific region in order to understand the causes of large negative departures of ISMR. The monthly mean Outgoing Long-wave Radiation (OLR) data from January 1975 to May 2004 from NOAA’s polar orbiting satellites are used in this study. Similarly, the convective activity over the Northwest (NW) Pacific associated with the typhoon activity over the region, as represented by the daily frequency and positions of typhoon activity over the NW Pacific region for 53 years (1950 to 2002) is also used to find out its impacts on ISMR.

The evolution of OLR (thus, convection) anomalies over the Indo-Pacific regions shows contrasting patterns from January to May preceding the excess and deficient monsoon years with significant correlation coefficient with the ensuing monsoon rainfall over India. It is also observed that a statistically significant negative simultaneous correlation between typhoon days over NW Pacific and July rainfall over India has been observed. Spatial dependence of the relationship revealed that typhoons forming over NW Pacific east of 1500E and moving northwards have an adverse effect on ISMR. It is also observed that typhoons forming over the South China Sea and moving westwards may have a positive impact on monsoon rainfall over India. Enhanced typhoon activity over NW Pacific during July 2002 induced weaker monsoon circulation over the Indian region due to large-scale subsidence.

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