Effects of dynamic heat fluxes on model climate sensitivity: Meridional sensible and latent heat fluxes

Abstract

We incorporate physically based parameterizations of atmospheric meridional heat fluxes into the climate model of Wang et al. (1984) to study their effects on climate changes caused by increases of CO2 abundance and solar constant variations. The physically based parameterizations calculate both the magnitudes and profiles of the sensible and latent heat fluxes in good agreement with observations. Comparisons of climate sensitivity between the physically based parameterizations and the original model's empirical parameterization for total transport are performed. The results indicate that both parameterizations yield about the same changes in global mean surface temperature and ice line, but the physically based parameterizations produce smaller changes in meridional temperature gradient. Also, the sensible and latent heat fluxes from the physical parameterization produce mutually compensating changes which are consistent with general circulation model results. We also study the separate feedback effects of sensible and latent heat fluxes by allowing only one or the other to change during climate changes. It is found that these variations in the partitioning of changes in the meridional heat transport have relatively small effects on the change of hemispheric mean surface temperature, but they can affect both the sign as well as the magnitude of the change of meridional temperature gradient. The change in total meridional heat transport is also relatively insensitive to the partitioning variations. Further analysis of the model's energy balance indicates that this insensitivity is a consequence of two features of the results: (1) absorption of the latitudinally varying part of the solar heating is affected very little by the partitioning, and (2) thermal structure changes that are affected by the partitioning do not influence greatly the zonal energy balance.