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Published May 2015 | Published
Journal Article Open

Interannual Variability in the Large-Scale Dynamics of the South Asian Summer Monsoon


This study identifies coherent and robust large-scale atmospheric patterns of interannual variability of the South Asian summer monsoon (SASM) in observational data. A decomposition of the water vapor budget into dynamic and thermodynamic components shows that interannual variability of SASM net precipitation (P − E) is primarily caused by variations in winds rather than in moisture. Linear regression analyses reveal that strong monsoons are distinguished from weak monsoons by a northward expansion of the cross-equatorial monsoonal circulation, with increased precipitation in the ascending branch. Interestingly, and in disagreement with the view of monsoons as large-scale sea-breeze circulations, strong monsoons are associated with a decreased meridional gradient in the near-surface atmospheric temperature in the SASM region. Teleconnections exist from the SASM region to the Southern Hemisphere, whose midlatitude poleward eddy energy flux correlates with monsoon strength. Possible implications of these teleconnection patterns for understanding SASM interannual variability are discussed.

Additional Information

© 2015 American Meteorological Society. Received: September 2, 2014; Final Form: December 24, 2014. This work was supported by a Natural Sciences and Engineering Research Council of Canada Postgraduate Scholarship, the Caltech Terrestrial Hazard Observation and Reporting Center, and National Science Foundation Grants AGS-1019211 and AGS-1049201. The data analyses were conducted on Caltech's Division of Geological and Planetary Science CITerra computing cluster.

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