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GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L05804, doi:10.1029/2007GL032901, 2008

Modelling the influence of North Atlantic multidecadal warmth on the Indian summer rainfall

Shuanglin Li

Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Beijing, China.


Judith Perlwitz

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.
Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA.


Xiaowei Quan

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.
Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA.


Martin P. Hoerling

Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA.


Abstract

Ensemble experiments with an atmospheric general circulation model reveal that a positive (warm) ocean phase of the Atlantic Multidecadal Oscillation (AMO) increases Indian summer rainfall. The intensification is driven by extratropical North Atlantic warmth, with some cancellation associated with monsoon weakening in response to tropical North Atlantic warmth. Mechanistically, warm extratropical North Atlantic SSTs increase local rainfall, inducing an arching extratropical wavetrain response. The latter leads to intensified northern subsidence of monsoon mean meridional streamflow as well as widespread low surface pressure over North Africa, the Middle East and the western Indian Ocean contributing to a strengthened Indian monsoon trough and increased monsoon rainfall. Warm tropical North Atlantic SSTs primarily increase local tropical Atlantic rainfall that induces a tropically-confined response consisting of low level easterly wind anomalies over the Indian Ocean and dynamically induced subsident drying over India.

Received 5 December 2007; accepted 30 January 2008; published 5 March 2008.

Keywords: Atlantic Multidecadal Oscillation; Indian summer rainfall; monsoon.

Index Terms: 0429 Biogeosciences: Climate dynamics (1620); 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504); 3354 Atmospheric Processes: Precipitation (1854); 3337 Atmospheric Processes: Global climate models (1626, 4928).

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Citation: Li, S., J. Perlwitz, X. Quan, and M. P. Hoerling (2008), Modelling the influence of North Atlantic multidecadal warmth on the Indian summer rainfall, Geophys. Res. Lett., 35, L05804, doi:10.1029/2007GL032901.