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Paradox in South Asian summer monsoon circulation change: Lower tropospheric strengthening and upper tropospheric weakening
Author(s) -
Ma Jian,
Yu JinYi
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl059891
Subject(s) - troposphere , climatology , environmental science , stratification (seeds) , precipitation , atmospheric sciences , coupled model intercomparison project , monsoon , moisture , advection , circulation (fluid dynamics) , atmospheric circulation , south asia , general circulation model , climate change , geology , meteorology , geography , oceanography , physics , seed dormancy , history , botany , germination , ethnology , dormancy , biology , thermodynamics
In the literature, there exist contradictory conclusions on the South Asian summer monsoon (SASM) precipitation and circulation changes: whether the circulation change contributes positively by strengthening or negatively by weakening to the rainfall enhancement, on a background of moisture content increase. Based on Representative Concentration Pathway 4.5 simulations by 18 Coupled Model Intercomparison Project phase 5 models, this study explains these puzzles by illustrating that the SASM circulation changes oppositely between the lower and upper troposphere, with tipping point at 450 hPa. However, this indicates a new paradox, created by competing mechanisms. By analyzing the intermodel variability, we determine that the mean advection of stratification change mechanism weakens the upper tropospheric circulation, while the enhanced surface land‐sea thermal contrast strengthens the lower level and surface winds. Our moisture budget analysis shows that the SASM precipitation enhancement (8% K −1 ) attributes to moisture increase (5% K −1 ) and lower tropospheric circulation strengthening (3% K −1 ).