Modulation of Indian summer monsoon through northern and southern hemispheric extra-tropical oscillations

The Indian summer monsoon is a highly energetic global atmospheric circulation system. Although the El Nino Southern Oscillation (ENSO) has been statistically effective in explaining several past droughts in India, in recent decades the ENSO-monsoon relationship has weakened over the Indian subcontinent. In this context, a teleconnection with other dominant modes is of interest. The present study focuses on the mutual impact of the North Atlantic Oscillation (NAO) and Southern Annular Mode (SAM) on the regional variability of the Indian summer monsoon. Strong El Nino and La Nina years are excluded to find the interaction between extratropics and Indian summer monsoon. During the synchronous effect of these extratropical modes, the intensity as well as the spatial distribution of rainfall anomalies varies significantly in the western coastal region, eastern part of central and northeast India. The decrease in rainfall along the southwest coastal regions is related to the reduced zonal moisture transport. Significant reduction in moisture transport occurs in the positive phase of SAM and the negative phase of the NAO. The thermal gradient developed between the Indian landmass and southern tropical ocean differs significantly during the simultaneous impact of these modes. Moreover, the spatial variation and change in intensity of summer monsoon (July–August) parameters associated with SAM depend on the respective phase of the NAO. These results will help to open new areas of research on the simultaneous teleconnection of the two hemispheric modes on circulation features and weather systems.