Pré-Publication, Document De Travail (Preprint/Prepublication) Année : 2024

Atmosphere Response to an Oceanic Sub-mesoscale SST Front: A Coherent Structure Analysis

Alex Ayet
Fleur Couvreux

Résumé

The atmosphere response to oceanic submesoscale sea surface temperature (SST) fronts is neither resolved by operational nor climate models. Above the ocean, the atmospheric boundary layer (ABL) is in a convective regime and its turbulence levels and structure are altered by the SST variations. Using large eddy simulations, we investigate an ABL flowing above an idealized oceanic submesoscale SST front in a channel configuration. The atmosphere organization evolves from rolls to a cell-roll transition state but with a 5 km delay due to the strong advection. The SST gradient imprints into the atmosphere, generating a pressure gradient that accelerates the flow at all altitudes. On warm water, horizontal wind in the lower half of the ABL is increased mainly by turbulent mixing. Most of the flow is resolved, and we relate statistical quantities to coherent structures using a conditional sampling. The SST increase induces enhanced updrafts and in response a downward motion sets up, transporting high wind from the upper to the the lower layers of the ABL. We show that this descending flow is not a downdraft but rather a less turbulent object, similar to an enhanced compensating subsidence, that could be parametrized by a mass-flux term. The intense updrafts overshoots the boundary layer height and could trigger convection with moister environmental conditions.

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Dates et versions

hal-04729066 , version 1 (09-10-2024)
hal-04729066 , version 2 (26-11-2025)

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  • HAL Id : hal-04729066 , version 1

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Hugo Jacquet, Alex Ayet, Fleur Couvreux. Atmosphere Response to an Oceanic Sub-mesoscale SST Front: A Coherent Structure Analysis. 2024. ⟨hal-04729066v1⟩
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