The influence of El Niño on the Indian summer monsoon rainfall anomaly: a diagnostic study of the 1982/83 and 1997/98 events

Abstract

The Indian summer monsoon of 1982 and 1997 depicts disparities, however, maximum sea surface temperature anomaly over Nino 3 region is observed in the following winter of both the years. The inter-annual variation of sea surface temperature anomaly shows maximum peak during 1982/83 and 1997/98 El Nino events. The inter-annual variation of multivariate ENSO index also supports the above observation. The analyses of the entire tropical Pacific basin including the equatorial region reveal an anomalous behavior of the mean sea level pressure (MSLP) and the convective activities. The observations further reveal that the negative anomaly in monsoon rainfall over India prevails throughout the monsoon season except for the month of August in 1982, while in the year 1997 the monsoon rainfall anomaly shows random variations. The comparison between the summer monsoon rainfall of 1982 and 1997 depicts that the magnitude of the positive anomaly is same in the month of August. The condition over tropical Pacific during 1982/83 and 1997/98 has been investigated through the variation of outgoing long wave radiation (OLR), MSLP and pressure vertical velocity. The time–longitude plots of OLR and MSLP reveal the changes in pressure distribution and convective pattern over the tropical equatorial Pacific. The zonal and meridional cross section of pressure vertical velocity over the tropical Pacific and tropical Indian Ocean facilitates to understand the strength of the vertical motion during the monsoons of 1982 and 1997.