On the Prediction of India Monsoon Rainfall Anomalies

Abstract

Abstract A complex of anomalies in the premonsoon large-scale circulation setting heralds the interannual variability of India summer monsoon rainfall. The most prominent precursors of precipitation anomalies are the latitude position of the upper-air ridge over India, apparently reflecting the persistence of the boreal winter wind regime and its consequence for the establishment of the summer upper-air circulation; the temperature in southern Asia and the adjacent North Indian Ocean waters, a factor instrumental in heat-low development and hence the establishment of meridional pressure gradients and lower-tropospheric airstreams from the Southern Hemisphere; and indices of the Southern Oscillation, capturing pressure departure patterns spanning the global tropics. Stepwise multiple regression is used to extract from this “anomaly complex” the variance most pertinent to the interannual variability of Southwest monsoon rainfall, observations of pertinent elements being available for the period 1939–81. Reg...