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Published November 28, 2016 | Published + Supplemental Material
Journal Article Open

Onset and withdrawal of the large-scale South Asian monsoon: A dynamical definition using change point detection


We introduce an objective definition for onset and withdrawal of the South Asian summer monsoon (SASM), based on the large-scale atmospheric moisture budget. The change point (CHP) index allows precise characterization of the different stages and timescales of the large-scale SASM and is highly correlated with the local operational index, the monsoon onset over Kerala. The CHP-based onset and withdrawal dates, which capture the expected seasonal transitions in rainfall and winds, correspond with regime changes in the SASM moisture budget between negative and positive net precipitation. Climatological composites reveal that the seasonal transitions in SASM sector mean precipitation and circulation closely resemble those of the zonal mean Hadley circulation. The CHP index at grid points within the SASM domain yields a robust definition of local onset and withdrawal dates, which are well correlated with the large-scale index on interannual timescales, providing insight into the regional variability of the SASM.

Additional Information

© 2016 American Geophysical Union. Received 2 SEP 2016; Accepted 4 NOV 2016; Accepted article online 14 NOV 2016; Published online 22 NOV 2016. This work was supported by the Caltech Terrestrial Hazard Observation and Reporting (THOR) Center. We thank Sabin TP for providing MOK data from the IMD. Reanalysis and precipitation data sources are cited in the text and referred to in the references list. MERRA-2 data are available at http://disc.sci.gsfc.nasa.gov/mdisc/. GPCP data are available at http://precip.gsfc.nasa.gov/. All other data and source code necessary to reproduce this analysis are available from the authors upon request (jwalker@caltech.edu).

Attached Files

Published - Walker_et_al-2016-Geophysical_Research_Letters.pdf

Supplemental Material - grl55223-sup-0001-supinfo.pdf


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