Influence of Indian Ocean Dipole on Poleward Propagation of Boreal Summer Intraseasonal Oscillations

The influence of the Indian Ocean dipole (IOD) on the poleward propagation of boreal summer intraseasonal oscillations (BSISOs) is examined using observed datasets. This study finds that coherent (incoherent) poleward propagation of precipitation anomalies from 5 degrees S to 25 degrees N are observed during negative (positive) IOD years. Disorganized poleward propagation of BSISO in the south equatorial Inidan Ocean is observed during positive IOD years. The rationale behind such an anomaly in the poleward propagation of BSISO in contrasting IOD years identified based on the theory of northward-propagating BSISO, which suggests the influential role of air-sea interaction on the genesis and propagationof BSISO. It is found that the mean structure of moisture convergence and meridional specific humidity distribution undergoes radical changes in contrasting IOD years, which in turn influences the meridional propagationof BSISO. This study assumes significance, considering the critical role of BSISO in modulating the seasonal mean summer monsoon rainfall.