Air-Sea Interaction Plays a Different Role in North Pacific Turbulent Heat Flux Exchange in Summer Versus Winter

The variation of latent and sensible turbulent heat fluxes is vital in large-scale sea surface temperature (SST) variability in the Northern Hemisphere extratropics. Turbulent heat fluxes thus play a key role in the Northern Hemisphere extratropical region in regulating climate variability through SST. In this study, we investigate the linkages between seasonal variations of anomalous turbulent heat fluxes, the underlying SST, and the near-surface wind speed. Preliminary findings based on the ERA5 reanalysis and the NCAR CESM1-CAM4 model show that the linear proportional relationship between turbulent heat fluxes and the prevailing wind does not hold in the North Pacific during summertime. For instance, there is an increase in the latent heat release out of the ocean in the northern hemisphere extratropics during the summer months when the prevailing wind is the lowest. An NCAR CESM1-CAM4 model hierarchy incorporating a fully-coupled model, slab ocean model, and mechanically decoupled model is used to better understand the relative importance of a dynamic ocean, wind-driven ocean variability and the atmosphere in driving these seasonal variations of turbulent heat fluxes. Mechanical decoupling refers to disengaging the anomalous momentum coupling between the atmosphere and ocean by overwriting the fully coupled, time-varying momentum flux with a climatological momentum flux. Additionally, an AMIP simulation with prescribed time-varying SST is used to determine the contribution of oceanic forcing to the seasonal variations of turbulent heat fluxes in the targeted region. Analysis of the coupled model hierarchy suggests that wind-driven ocean dynamics may be important in seasonal changes of the North Pacific air-sea interactions.