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Sheehan, Peter M. F. 
ORCID: https://orcid.org/0000-0002-4906-5724, Matthews, Adrian J. ORCID: https://orcid.org/0000-0003-0492-1168, Webber, Benjamin G. M. ORCID: https://orcid.org/0000-0002-8812-5929, Sanchez-Franks, Alejandra, Klingaman, Nicholas M. and Vinayachandran, P. N.
(2023)
On the influence of the Bay of Bengal's sea surface temperature gradients on rainfall of the South Asian monsoon.
Journal of Climate, 36 (18).
6499–6513.
ISSN 0894-8755
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Abstract
The southwest monsoon delivers over 70% of India's annual rainfall and is crucial to the success of agriculture across much of South Asia. Monsoon precipitation is known to be sensitive to sea surface temperature (SST) in the Bay of Bengal (BoB). Here, we use a configuration of the Unified Model of the UK Met Office coupled to an ocean mixed layer model to investigate the role of upper-ocean features in the BoB on southwest monsoon precipitation. We focus on the pronounced zonal and meridional SST gradients characteristic of the BoB; the zonal gradient in particular has an as-yet unknown effect on monsoon rainfall. We find that the zonal SST gradient is responsible for a 50% decrease in in rainfall over the southern BoB (approximately 5 mm day-1), and a 50% increase in rainfall over Bangladesh and northern India (approximately 1 mm day-1). This increase is remotely forced by a strengthening of the monsoon Hadley circulation. The meridional SST gradient acts to decrease precipitation over the BoB itself, similarly to the zonal SST gradient, but does not have comparable effects over land. The impacts of barrier layers and high-salinity sub-surface water are also investigated, but neither has significant effects on monsoon precipitation in this model; the influence of barrier layers on precipitation is felt in the months after the southwest monsoon. Models should accurately represent oceanic processes that directly influence BoB SST, such as the BoB cold pool, in order to faithfully represent monsoon rainfall.
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| Additional Information: | Acknowledgments: The Bay of Bengal Boundary Layer Experiment, jointly funded by the Ministry of Earth Sciences (India) and NERC/UKRI (United Kingdom), supported PMFS, BGMW and AJM (NE/L013827/1), ASF (NE/L013835/1), and PNV. NPK was supported by a NERC Independent Research Fellowship (NE/L010976/1). Part of the research presented in this paper was carried out on the High Performance Computing Cluster supported by the Research Computing Service at the University of East Anglia. PMFS thanks Andy Heaps and Liang Guo, both of the National Centre for Atmospheric Sciences (Reading, United Kingdom) for assistance in accessing archived model output and for assistance with the WAM-2layers moisture-tracking model respectively. Data availability statement. The code of the MetUM is available only under license from the UK Met Office; for details, see www.metoffice. gov.uk/research/modelling-systems/unified-model. Output relevant to this paper has been archived at https://figshare.com/articles/dataset/Sheehan_et_al_2022_MetUM_output/19620975. The WAM2layers model code is available at github.com/ruudvdent/WAM2layersPython/tree/distance/. |
| Uncontrolled Keywords: | atmosphere-ocean interaction,general circulation models,indian ocean,monsoons,rainfall,sea surface temperature,atmospheric science ,/dk/atira/pure/subjectarea/asjc/1900/1902 |
| Faculty \ School: | Faculty of Science > School of Environmental Sciences Faculty of Science > School of Natural Sciences (former - to 2024) University of East Anglia Research Groups/Centres > Theme - ClimateUEA |
| UEA Research Groups: | Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences Faculty of Science > Research Groups > Climatic Research Unit Faculty of Science > Research Groups > Fluids & Structures Faculty of Science > Research Groups > Numerical Simulation, Statistics & Data Science |
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| Depositing User: | LivePure Connector |
| Date Deposited: | 07 Jun 2023 10:30 |
| Last Modified: | 04 Dec 2024 01:39 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/92304 |
| DOI: | 10.1175/JCLI-D-22-0288.1 |
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