Influence of Pre-onset Land-Atmosphere conditions on the Indian Summer Monsoon Rainfall variability

A possible link between antecedent/pre-onset land-atmospheric conditions and the Indian summer monsoon rainfall (ISMR) is explored based on observed and reanalysis data. It is shown that, the pre-onset positive (negative) rainfall anomaly over northwest India, Pakistan, Afghanistan and Iran is associated with decrease (increase) in the ISMR, primarily in the months of June and July, which in turn affects the seasonal mean. ISMR in the months of June and July is also strongly linked with the pre-onset 2m air temperature over the same regions. The pre-onset rainfall/2m air temperature variability appears to be linked with midlatitude processes, which is evident from the associated wave activity flux. As the predictability of Indian summer monsoon relies mainly on the El Niņo Southern Oscillation (ENSO), the found link may further enhance our ability to predict the monsoon particularly during a non-ENSO year. This study identifies one more predictor for the first two months (i.e. June and July) of the monsoon season, which will be immensely useful for further pushing the upper limit of model ISMR skill score by including the variability generated by pre-onset rainfall.