Pivotal Role of Mixed‐Layer Depth in Tropical Atlantic Multidecadal Variability

Abstract 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 hea...

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Bibliographic Details
Published in:Geophysical Research Letters
Main Authors: Balaji Senapati, Christopher H. O’Reilly, Jon Robson
Format: Article in Journal/Newspaper
Language:English
Published: Wiley 2024
Subjects:
North Atlantic
ocean‐atmosphere coupling
Atlantic Multidecadal Variability
tropical variability
Geophysics. Cosmic physics
QC801-809
Online Access:https://doi.org/10.1029/2024GL110057
https://doaj.org/article/468ccd18437a4fd381b9a0aa66db2d04
Description
Summary:Abstract 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.

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