Teleconnections of Indian monsoon rainfall with AMO and Atlantic tripole
The teleconnections between the decadal modes in the Indian monsoon rainfall (IMR) and the North Atlantic sea surface temperature are investigated. The two decadal modes of variability in the North Atlantic, the Atlantic multidecadal oscillation (AMO) and the Atlantic tripole, have opposite relation with the two decadal modes of IMR. The AMO has positive correlation with the monsoon rainfall while the Atlantic tripole has negative correlation. This study has put forward hypotheses for the mechanisms involved in the teleconnections of the AMO and the Atlantic tripole with the IMR. The warm phase of AMO may influence the monsoon through the summer North Atlantic Oscillation (SNAO) and further through the equatorial zonal winds which increase the moisture flow over India by enhancing the southwesterly flow. The warm phase of Atlantic tripole may impact the monsoon through the all-season NAO, leading to decreased moisture flow over India through the equatorial wind pattern. The observed relations between the decadal modes in the North Atlantic and the Indian monsoon are explored in the simulations of National Center for Atmospheric Research Community Climate System Model version 4 (CCSM4) model. Although the model supports the observed decadal teleconnection between the Atlantic Ocean and Indian monsoon, it has limitations in capturing the details of the spatial pattern associated with the teleconnection. The teleconnections of AMO and Atlantic tripole with the Indian monsoon is further demonstrated through an experiment with CCSM4 by decoupling the North Atlantic Ocean. The hypotheses for the mechanisms of the Atlantic teleconnections are also explored in the CCSM4 simulation.
KeywordsIndian monsoon AMO Atlantic tripole NAO NCAR CCSM4 Decadal variability
This work was supported by grants from National Science Foundation (ATM-0830062 and ATM-0830068), National Oceanic and Atmospheric Administration (A09OAR4310058), and National Aeronautics and Space Administration (NNX09AN50G). The authors thank National Center for Atmospheric Research for computer time, the model control data and technical help with model experiments, and Bohua Huang and Yohan Ruprich-Robert for helpful discussions. We also thank two anonymous reviewers for their insights which has helped to improve this manuscript. This work formed a part of the Ph.D. thesis of Lakshmi Krishnamurthy at George Mason University.
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