The impact of a uniform ocean warming on the West African monsoon

Mutton, Harry; Chadwick, Robin; Collins, Matthew; Lambert, F. Hugo; Taylor, Christopher M. ORCID: https://orcid.org/0000-0002-0120-3198; Geen, Ruth; Todd, Alexander. 2024 The impact of a uniform ocean warming on the West African monsoon. Climate Dynamics, 62 (1). 103-122. https://doi.org/10.1007/s00382-023-06898-1

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Abstract/Summary

Projections of West African Monsoon (WAM) precipitation are uncertain. To address this, an improved understanding of the mechanisms driving WAM precipitation change is needed to shed light on inter-model differences and aid model development. The full forcing of increased CO2 can be decomposed into different components such as the impact of ocean warming, or the direct radiative effect of increased CO2. This paper investigates such a decomposition, analysing the effect of a uniform 4K ocean warming whilst keeping atmospheric CO2 concentrations constant. The analysis highlights several mechanisms acting to decrease WAM precipitation over a range of timescales, from days after the abrupt ocean warming, to the long-term equilibrium response. The initial decrease in WAM precipitation is caused by warming and enhanced convection over the ocean, stabilising the atmosphere inland and disrupting the monsoon inflow at low levels. Later in the response (after about 5 days), the WAM precipitation is reduced through a strengthening of the shallow circulation over West Africa, associated with changes in the large-scale temperature gradients and a local warming of the atmosphere related to a soil moisture feedback mechanism over the Sahel. Finally, from around 20 days after the SST increase, the WAM precipitation is also reduced through changes in specific humidity gradients that lead to increased potency of dry air advection into the monsoon rainband. The analysis concludes by demonstrating that the processes affecting precipitation in the early stages of the response are also relevant to the long-term equilibrium response.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1007/s00382-023-06898-1
UKCEH and CEH Sections/Science Areas:	Hydro-climate Risks (Science Area 2017-)
ISSN:	0930-7575
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	Africa, monsoons, atmosphere, climate change
NORA Subject Terms:	Meteorology and Climatology Atmospheric Sciences
Date made live:	09 Nov 2023 10:52 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/535845

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