Seasonal cycle and intraseasonal oscillations in the interannual variability over the monsoon region

Abstract

A characteristic seasonal cycle in the interannual variability (IAV) of dynamical fields over the Indian summer monsoon (ISM) region is revealed by an investigation of daily fields from a 40-year global data set from NCEP. The IAV, measured in terms of standard deviation, is remarkably suppressed over the monsoon region during June to September. Time-latitude distribution of IAV shows that a suppression of IAV in the summer months is a general feature, if not as pronounced as over ISM, of the northern hemisphere. Other new features revealed by our analysis are (a) a differential, nearly out of phase behaviour between zonal and meridional wind components north of 30N, and (b) strong intraseasonal oscillations in IAV, which are once again suppressed during the monsoon months. The low IAV implies a weaker contrast in these fields for different years; implications of this feature for long range forecasting of monsoon are discussed. Copyright 2005 by the American Geophysical Union.