Quantifying the Role of Ocean Dynamics in SST Variability across GCMs and Observations
Numerous studies in the past two decades have investigated the role of ocean dynamics in regions where the ocean plays an active role in driving SST, most notably in western boundary current systems. We examine the strength of this influence as a function of model resolution and identify intensification in high-resolution models, due to both ocean dynamics and surface fluxes.
Midlatitude SSTs forced by mesoscale oceanic processes can affect the large-scale atmosphere, pointing to the ocean's crucial role outside the tropics. Previous studies have shown the effect of oceanic mesoscale processes on global and regional climate variability. This study quantifies the local contribution of ocean dynamics to mixed-layer temperature across the globe by directly estimating the ocean heat flux divergence resolved by state-of-the-art ocean reanalysis, eddy-resolving, and eddy-parameterized versions of two US national climate models and indirectly from air-sea flux satellite-based estimates. Our results show that the eddy-resolving climate simulations resolve mixed-layer temperature variances that are larger and closer to those inferred from observations than both their eddy-parameterized counterparts and ECCO over much of the extratropics.
Our analysis reveals an important and previously unidentified sensitivity for mixed-layer SST variability as a function of model resolution, suggesting a contribution from processes that are poorly resolved in low-resolution models such as ocean eddies and fronts.