The paper investigates the extent to which the climatic mechanisms generated by the recently identified Indian Ocean Dipole (IOD) and its atmospheric component the Equatorial Indian Ocean Oscillation (EQUINOO) have influenced inter-annual variability of Southern Oman Summer Monsoon (SOSM) rainfall basing on data for the period 1985-2005. It has been identified elsewhere that the interplay of ENSO and the IOD mode can lead to different patterns of Sea Surface Temperature (SST) and Outgoing Long Wave Radiation (OLR) anomalies over the Equatorial Indian Ocean with different implications for the monsoon system in the region. The paper presents the results of an analysis of the possible relations of the inter-annual variation in SOSM with atmospheric convection and circulation over the equatorial Indian Ocean and ENSO. It could be advocated that the IOD and the El Nino/Southern Oscillation (ENSO) have complementarily affected the SOSM during the last four decade. The IOD exercised substantial role, first, through its influence as a modulator of the SOSM and, second, though its impact on the correlation between the SOSM and ENSO. Basing on the analysis of available data, the ENSO-induced anomalous circulation over Arabian Sea is either countered or supported by the IOD, depending upon the state of the phase and the amplitude of the two.
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