Surface Divergent Eddy Heat Fluxes and Their Impacts on Mixed Layer Eddy-Mean Flow Interactions

In this study, the global surface divergent eddy heat flux (EHF) is estimated using remote sensing observations of sea surface height (SSH) and sea surface temperature (SST) over two decades (1993-2017). These results are used as a metric to assess model fidelity in a mesoscale eddy-resolving version of the Community Earth System Model. The estimated EHFs show that the midlatitudes significantly contribute to the poleward transport of heat because of strong regional variability in SSH and SST. A Helmholtz decomposition is performed on the global EHFs to remove prominent nondynamic rotational wave-like structures that appear in these fluxes. The dynamic divergent EHFs are responsible for driving cross-frontal exchange and positive Baroclinic Conversion (BC) rates, suggesting a conversion of mean potential energy to eddy potential energy within the mixed layer. The results show that the model captures the same spatial patterns of EHFs and BC rates, but with relatively higher values in the midlatitudes than observations. The mixed layer geostrophic meridional eddy heat transport reaches maximums of 0.07 PW and 0.1 PW in the midlatitudes in the observations and climate model, respectively. The global integrated BC rate is 0.11 TW in the observations, which is similar to 30% weaker than the climate model (0.16 TW). A cross-spectral analysis further shows that the model has higher energy in low-frequency bands for periods greater than 10 months in the northern hemisphere western boundary currents, but can capture the major spectral peaks in EHFs that are seen in observations.