Oceanic latent heat fluxes: Consistency with the atmospheric hydrological and energy cycles and general circulation modeling

摘要

Traditional climatological estimates of oceanic latent heat fluxes are significantly lower than those obtained from general circulation models (GCMs). A recent satellite-based climatology yields higher latent heat fluxes, which are in closer agreement with those implied by measurements of ocean heat transports. This motivates a review of the consistency of the atmospheric energy and hydrological cycles as represented by current climatologies. Depending on the combination of climatologies selected, mean imbalances of up to ±13 W m-2 are found in the hydrological cycle over the oceans. The energy cycle shows a lack of net atmospheric absorption for all combinations of climatologies, except those involving constrained surface radiative fluxes: With unconstrained climatologies the global annual mean imbalance in the energy cycle lies in the range -13 to -38 W m-2. A seasonal analysis of the energy cycle shows significant regional imbalances in the winter hemisphere and suggests that it would be premature to focus on the surface shortwave radiation alone to explain imbalances in this cycle. The simulation of the latent heat fluxes in the Met Office's GCM is compared with climatological data, considering the exchange coefficient, the wind speed and the specific humidity. A revision to the exchange coefficient for moisture reduces it to values in closer agreement with recent field observations. Small decreases in the oceanic latent heat fluxes result, reducing the discrepancy with the climatologies, while the atmosphere is cooled and dried.