A surface-renewal based composite model of the bulk-skin sea surface temperature difference

Analysis of several datasets containing measurements of the bulk-skin sea surface temperature difference (DT) and corresponding environmental parameters indicate that existing models for DT still fail to capture much of the observed variability. Failure to properly account for DT may lead to increased uncertainties or errors in heat flux computations and coupled air-sea modeling studies. New results suggest the potential for further improving our ability to predict DT. Our new composite model is derived from a linear combination of traditional and newly developed surface renewal time scales. The included time scales more completely cover the full range of relevant physical processes from free convection to wave effects due to the presence of capillary and small gravity waves. A time scale for the renewal of the skin layer based on convective theory provides an excellent limit for the magnitude of DT both inside and out of the expected convective regime. New time scales consist of power series expansions of the convective time scale. The relative effects of the different physical processes are determined by weighting functions on the individual time scales. The weighting functions are derived in part from the heat flux and incorporate dependence on both the Rayleigh and Richardson numbers. The composite model exhibits very high correlations with an extensive and highly diverse set of direct measurements of DT from oceanographic cruises. Some assumptions of the model are further evaluated against a numerical molecular diffusion model for the near-surface temperature profile.