Interactions between the summer mean monsoon and the intraseasonal oscillation in the Indian monsoon region

The relationship between interannual variations of the seasonal mean monsoon and intraseasonal oscillation (ISO) during boreal summer over the Indian monsoon region is investigated. The result shows a negative correlation between all-India summer monsoon rainfall and the ISO intensity. It is argued that the negative correlation is primarily attributed to the impact of the mean state of Indian summer monsoon on ISO. A strong Indian monsoon leads to the weakening of convection over the equatorial eastern Indian Ocean. The latter may further suppress the eastward and northward propagating ISO variances over the Indian Ocean and lead to a weakened intraseasonal activity over the Indian monsoon region. The ISO may feed back to the Indian summer mean monsoon through nonlinear eddy momentum transport. In addition, the ISO intensity over India increases (decreases) during the ENSO developing (decaying) summers.