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

• Published in: Journal of climate Vol. 28; no. 9; pp. 3731 - 3750
• Main Authors: Walker, Jennifer M., Bordoni, Simona, Schneider, Tapio
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01-05-2015
• Subjects: Atmospheric circulation; Atmospheric moisture; Atmospheric temperature; Brackish; Budgets; Climate change; Datasets; El Nino; Energy flux; Energy transfer; Equatorial circulation; Influence; Interannual variability; Marine; Meteorology; Moisture effects; Monsoon circulation; Monsoons; Observational studies; Precipitation; Rain; Rainy seasons; Regression analysis; Sea breezes; Southern Hemisphere; Studies; Summer; Summer monsoon; Teleconnection patterns; Teleconnections; Temperature; Variability; Water vapor; Water vapor budget; Water vapour; Wind; Winds; Indian Ocean; Tibetan Plateau
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-14-00612.1

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.