Lia Siegelman (Scripps Institution of Oceanography, University of California San Diego, United States); Luc Lenain (Scripps Institution of Oceanography, University of California San Diego, United States); Dimitris Menemenlis (Moss Landing Marine Laboratories, San José State University, United States); Andrea Molod (NASA Goddard Space Flight Center, United States)

The Southern Ocean plays an outsized role in air-sea exchanges of heat and other climatically-relevant tracers. In particular, Latent Heat Fluxes (LHF) are the gateways through which moisture is transferred between the ocean and the atmosphere. Air-sea fluxes are known to be modulated by atmospheric variability and oceanic motions. In this study we aim to better understand the contributions of high-frequency atmospheric motions and fine ocean scales (e.g., submesoscales and high-latitude mesoscales) in the Southern Ocean.
We use a global, coupled ocean-atmosphere simulation that admits ocean submesoscales and atmospheric clouds, the so-called GEOS/ECCO C1440-LLC2160 simulation that has ~7-km horizontal grid spacing in the atmosphere and 2–4-km grid spacing in the ocean. The simulation reveals that LHF variability is primarily driven by atmospheric high frequencies (≳2days, e.g. up to 30% in Agulhas retroflection) and oceanic meso- and submesoscales (O(10–100 km) scales, e.g., up to 70% in Agulhas retroflection), with high spatial heterogeneity and distinct seasonal patterns throughout the Southern Ocean. By way of contrast, we also show that the commonly used LHF from ERA5 underestimate LHF variability by 20% on average across the entire Southern Ocean. These results highlight the potential of using SWOT data, in combination with high resolution SST observations, to more accurately diagnose high-latitude heat fluxes at the air-sea interface, fluxes that are at present especially poorly constrained.