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La Niña's Diminishing Fingerprint on the Central Indian Summer Monsoon
Author(s) -
Samanta Dhrubajyoti,
Rajagopalan Balaji,
Karnauskas Kristopher B.,
Zhang Lei,
Goodkin Nathalie F.
Publication year - 2020
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 - 10.1029/2019gl086237
Subject(s) - climatology , walker circulation , indian ocean , monsoon , environmental science , tropical cyclone , oceanography , subsidence , deep convection , atmospheric sciences , east asian monsoon , convection , geology , geography , structural basin , meteorology , paleontology
La Niña years tend to provide increased Indian summer monsoon (ISM) rainfall. However, observations show 6–8% reduction in ISM rainfall during post‐1980 La Niñas relative to pre‐1980. Using a suite of atmospheric general circulation model experiments, we replicate this observed phenomenon and attribute it to a combination of weakening La Niña events themselves plus strongly warming tropical Indian Ocean. We demonstrate that half of the ISM rainfall reduction during post‐1980 La Niñas can be attributed to changes in the spatial pattern and intensity of La Niña within the tropical Pacific Ocean. Warmer eastern‐equatorial Pacific Ocean temperatures during post‐1980 La Niñas weaken the Walker circulation, resulting in large‐scale anomalous subsidence over the Indian subcontinent, thereby inhibiting the deep convection that drives ISM rainfall. Further, we demonstrate the declining central ISM rainfall during La Niña years with increasing tropical Indian Ocean warming, which has several serious concerns for regional water resources and stability.