Extended winter Pacific North America oscillation as a precursor of the Indian summer monsoon rainfall

Abstract

In spite of considerable efforts, long-range forecasting of Indian summer monsoon rainfall (ISMR) is still a challenge for both statistical and dynamical tools. We highlight the winter-to-spring Pacific North America (PNA) oscillation as a predictor for the ISMR. A PNA-related index is proposed that is highly correlated with the following summer precipitation over India and is also a precursor of El Niño-Southern Oscillation (ENSO) events over recent decades. The PNA index compares well with other predictors used in operational statistical models for ISMR prediction. A multiple linear regression scheme is tested with a cross-validation hindcast approach and confirms the added value of our predictor, at least over the period 1958-2005. Nevertheless, the predictor shows less skill over the first half of the 20th century. Possible physical mechanisms of this teleconnection are also briefly discussed and could involve both a tropical Pacific sea surface temperature and Eurasian snow cover pathway. Copyright 2009 by the American Geophysical Union.