Role of mesoscale ocean variability in thermodynamic air-sea interactions in multi-century, high-resolution climate simulations

Abstract:

It is now well-known that mesoscale ocean currents can generate mesoscale sea surface temperature (SST) anomalies of sufficient magnitude and persistence to induce a response in surface turbulent heat fluxes (THF), with increasing evidence that this influence of mesoscale SSTs can play active roles in weather and climate. Despite the importance of such air-sea coupling regime, its spatial and temporal scales remain poorly constrained and it is still unclear whether it is only relevant over energetic extratropical current systems or can also be important at more quiescent oceanic regions. This study investigates these questions in multi-century climate model simulations from the International Laboratory for High-Resolution Earth System Prediction (iHESP) at both eddy-permitting high-resolution (HR) and eddy-parameterized low-resolution (LR) ocean resolutions with the Community Earth System Model version 1.3. Here, we use spectral methods to characterize the linear relationship between SST and THF and between SST-tendency and THF over scales between 10²-10⁴ km and 60 days-130 years across the global ocean. The relative roles of the ocean and the atmosphere in driving the observed linear relationships is inferred using analytical solutions of an energy balance model for the coupled air-sea system derived in spectral space.

In HR, our results show that the transition between ocean- and atmosphere-driven air-sea coupling regimes occurs at wavelengths near the atmospheric first internal Rossby deformation radius (~600-2000 km). This characteristic is seen across most latitudes of all three major ocean basins, also occurring at regions away from energetic current systems. The ocean-driven regime also shows a surprising temporal persistence, being present over much of the global ocean from periods as short as 60 days up to the truncation limit of the analysis at about 130 years. Such features are virtually absent in LR, suggesting that increasing model resolution can affect the SST and THF variability at not only mesoscales (<100 km) but also sub-basin scales (~1000 km), and from intraseasonal to multi-decadal temporal scales. Research is currently ongoing to determine the physical conditions in the ocean and the atmosphere that allow the prevalence of the ocean-driven regime over this wide range of scales.