Pivotal role of mixed-layer depth in Tropical Atlantic Multidecadal Variability

Senapati, B. ORCID: https://orcid.org/0000-0001-5029-9731, O'Reilly, C. H. ORCID: https://orcid.org/0000-0002-8630-1650 and Robson, J. ORCID: https://orcid.org/0000-0002-3467-018X (2024) Pivotal role of mixed-layer depth in Tropical Atlantic Multidecadal Variability. Geophysical Research Letters, 51 (15). e2024GL110057. ISSN 1944-8007 doi: 10.1029/2024GL110057

Abstract/Summary

The tropical arm of Atlantic Multidecadal Variability (AMV) influences climate worldwide, yet the mechanisms generating it remain unclear. Here, we examine experiments with sea surface temperature (SST)-restoring in the extratropical North Atlantic in multiple models and use mixed-layer heat budgets to elucidate the important mechanisms. Our results demonstrate that the tropical AMV is driven by wind-mixed-layer-SST feedback. The evolution has two phases with tropical AMV SST anomalies growing from April to October and decaying from November to March. The amplitude of the growth phase surpasses that of the decay phase, resulting in overall tropical Atlantic warming during positive AMV phases. During summer, positive SST anomalies in the extratropics weaken the trade winds, resulting in a shallower mixed-layer with reduced heat capacity. Subsequent absorption of climatological shortwave radiation in this shallower mixed-layer then causes SSTs to warm, generating the tropical AMV. Importantly, anomalous surface heat-fluxes make modest contributions to tropical AMV in these experiments.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/117647
Item Type	Article
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > NCAS Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Geophysical Union
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