Using an ensemble data set of turbulent air-sea fluxes to evaluate the IPSL climate model in tropical regions
Ocean-atmosphere interactions represent a key component of the hydrological cycle in tropical regions and their variability has profound influences on low-latitude climate. In order to evaluate how climate models represent these fluxes while taking into account the observational uncertainties, we assemble a comprehensive database of 14 climatological surface flux products, including in situ-based, satellite, hybrid, and reanalysis data sets. We find that the large observational uncertainties are reflected in the climatological magnitudes, as well as in the spatial patterns and seasonal variations and that, for the most part, they do not carry specific signatures of product type. This data ensemble allows us to draw several conclusions on the current representation of the intertropical turbulent air-sea fluxes in the atmospheric component of the Intitut Pierre Simon Laplace-Coupled Model 5A, when forced by observed sea surface temperatures. Despite significantly underestimated near-surface wind speeds over the entire tropical oceans domain, the atmospheric model produces generally well represented zonal and meridional wind stress values, and only weak biases in the spatial patterns and seasonality. The simulated latent heat flux develops a bias pattern matching that of the wind speed, but with no systematic underestimation. Compared to the same reference, the sensible heat flux is overestimated over the entire region of interest, in response to a significant overestimation of the sea-air temperature contrast. The observational ensemble and analyses presented in this paper offer a good framework for large-scale model surface flux evaluation.