Impacts of the Mesoscale Ocean‐Atmosphere Coupling on the Peru‐Chile Ocean Dynamics: Impact of the Thermal Feedback.

Consequences of the mesoscale Thermal FeedBack (TFB) on the ocean dynamics are studied in the South‐East Pacific (SEP) using a high‐resolution regional ocean–atmosphere coupled model. Three simulations are compared: the first one is a fully coupled simulation. In the second one, the TFB has been removed with an online smoothing of the Sea Surface Temperature (SST) conditions used by the atmosphere. In the third one, to disentangle the impact of the nearshore and the offshore TFB, the smoothing is only applied in the offshore region. In the SEP, the coastal upwelling cold tongue constitutes a permanent mesoscale SST pattern. We show that this SST pattern alters the coastal wind structure, reducing the coastal upwelling‐favorable wind intensity. So, the nearshore TFB reduces the coastal surface current and the vertical velocities. As a result, the Eddy Kinetic Energy (EKE) generation by baroclinic conversion is also weakened. In the offshore region, on the contrary, the oceanic mean state is not affected by the TFB and only the EKE is weakened. Composites above the coherent eddies show that the heat flux response to the mesoscale SST anomalies is responsible for the mesoscale activity weakening over the whole studied area. Although the wind response to the SST anomalies has a very weak mean impact on the EKE generation through wind work, we show that it strongly modifies the mean oceanic vertical velocity anomalies over the coherent eddies. Plain Language Summary: The ocean dynamics is usually seen as driven by the atmosphere. However, the influence between the ocean and the atmosphere is mutual and the oceanic surface conditions feedback on the atmosphere. In this paper, we focus on the response of the atmosphere to the sea surface temperature mesoscale structures (structures that ranges from a few tens of km to a few hundred km). This response, called Thermal Feedback (TFB), is modeled with a high‐resolution ocean‐atmosphere coupled model to investigate its consequences on the oceanic dynamics in the South‐East Pacific. This region is characterized by a wind‐driven upwelling of sub‐surface waters near the coast, forming a sea surface coastal cold tongue. We show that this structure alters in return the coastal wind structure, which contributes to reduce the upwelling and the surface current. The generation of mesoscale structures, such as coherent eddies and filaments, is also reduced. The mesoscale structures are also weakened in the offshore region. We analyze the atmospheric response above the coherent eddies and show that the heat flux response to the SST anomalies is responsible for the eddy damping. Vertical velocities are also created in the eddy by the wind response to the SST anomalies. Key Points: Mesoscale thermal feedback decreases the mean coastal upwelling‐favorable wind, surface current and nearshore eddy generationMesoscale thermal feedback on the heat fluxes decreases the coherent eddy intensity through baroclinic conversionCoherent eddy mean vertical velocity is strongly modified by the mesoscale thermal feedback [ABSTRACT FROM AUTHOR]