On the El Nino-Indian monsoon predictive relationships

Most of the severe droughts over India are associated with El Nino. However, only less than half of El Nino events are associated with deficient rainfall over India. In other El Nino years, Indian summer monsoon rainfall (ISMR) was either normal or excess. A recent study suggested that the El Nino events with the warmest SST anomalies in the central Pacific are more effective in focusing drought producing subsidence over India than events with the warmest SST anomalies in the eastern equatorial Pacific. They have further suggested that the incorporation of additional information on the spatial distribution of SST anomalies over the equatorial Pacific Ocean in the statistical models should improve monsoon forecast skill. The present study explores this hypothesis on the skill of monsoon forecasts by analyzing SST data for the period 1880 - 2004. The present study reveals that incorporation of information on the spatial pattern of SST anomalies ( by incorporating the Trans Nino Index) does not improve the association between El Nino and Indian monsoon rainfall. Simply using the SST index over the central Pacific (Nino-3.4) may be a better indicator for the association than the Combined Nino Index derived from Nino-3 and Trans Nino Index (TNI).