Sink of Eddy Energy by Submesoscale Sea Surface Temperature Variability in a Coupled Regional Model

Abstract Air–sea interaction impacts ocean energetics via modifications to the exchange of momentum and buoyancy. Prior work at the submesoscale has largely focused on mechanisms related to the eddy kinetic energy (EKE), such as the current feedback on stress, which generates negative wind work, or variations in sea surface temperature (SST) that modify surface winds. However, less is known about the influence of submesoscale SST variability on ocean energetics through its direct effect on the surface flux of available potential energy. In this work, the role of air–sea fluxes on submesoscale ocean energetics is investigated using a fully coupled model of the California Current region, including a numerical experiment that suppresses the thermal response in the computation of air–sea fluxes at the submesoscale. Correlations between surface buoyancy anomalies and surface buoyancy fluxes lead to an approximately 10%–20% loss of submesoscale eddy potential energy (EPE), which results in similar magnitude reductions of the vertical buoyancy production, EKE, and eddy wind work. The changes induced by this mechanism in the energy reservoirs and dissipation/conversion pathways are on the same order of magnitude as the negative wind work induced by the current feedback. A scaling for the EPE flux shows that it is a function of the density ratio and proportional to the surface EPE reservoir of the system. These findings indicate the importance of the submesoscale SST variability and small-scale variability in surface heat fluxes in modifying energy reservoirs and conversion pathways of the ocean via the direct flux of EPE at the air–sea interface. Significance Statement This work investigates the impact of small oceanic frontal features in the ocean, classified as submesoscale, on the exchange of energy at the air–sea boundary. Submesoscale fronts and filaments range from approximately 0.1–10 km and are characterized by strong horizontal density changes and fast-evolving flow. The associated density anomalies at the surface may be important in the overall energy budget of the surface ocean since they can affect the energy fluxes at the air–sea boundary. Two numerical experiments were set up for a comparative analysis of the energy transfer, conversion, and storage in the upper layer of the California Current region. One simulation works as a control experiment with air–sea fluxes calculated using the full-resolution fields. In the second experiment, the role of sea surface temperature anomalies in generating air–sea fluxes is suppressed. A comparison between the two experiments shows a difference of 10%–20% in the energy storage and conversion. Sea surface temperature variability may induce a reduction of energy via air–sea fluxes similar to energy dissipation driven by wind–current interactions on the same scale of phenomena.