Fast Warming of the Surface Ocean Under a Climatological Scenario

We examine various strategies for forcing ocean-only models, including an atmospheric boundary layer model. This surface forcing allows air-sea exchanges to affect atmospheric temperature and relative humidity, thus removing the assumption of an infinite atmospheric heat capacity associated with the prescription of these variables. When exposed to climatological winds, the simulated North Atlantic oceanic temperature warms considerably at the surface as compared to a model with full atmospheric variability. This warming is mainly explained by a weakened upper-ocean vertical mixing in response to the weakly varying climatological winds. Specifying the atmospheric temperatures inhibits this warming but depends on the unrealistic large atmospheric heat capacity. We thus interpret the simulated warmer ocean as a more physically consistent ocean response. We conclude the use of an atmospheric boundary layer model provides many benefits for ocean only modeling, although a “normal” year strategy is required for maintaining high-frequency winds.