The Surface Energy Balance and its Representation in CMIP5 Models
Abstract:Substantial uncertainties still exist in the quantification of the surface energy balance, and its representation in climate models. While the radiative exchanges at the top of atmosphere are now well known from satellite programs, the energy distribution at the Earth surface is less well determined. To better constrain the magnitudes of the surface radiative components we make extensive use of surface observations to constrain the radiation balance not only from space, but also from the surface. We combine these observations with the latest generation of climate models (CMIP5) to infer best estimates for the global, land and ocean mean surface radiative components. We determine the global mean downward surface solar and thermal radiation near 185 and 342 Wm-2, respectively, to be most compatible with surface observations. Combined with an estimated global mean surface absorbed solar radiation and thermal emission of 161 Wm-2 and 398 Wm-2, this leaves 105 Wm-2 of surface net radiation globally available for distribution amongst the non-radiative surface energy balance components. Over land, where most direct observations are available to constrain the surface fluxes , we obtain 185 and 305 Wm-2 for solar and thermal downward radiation, respectively. Over oceans, with weaker observational constraints, corresponding estimates are around 185 and 356 Wm-2. Considering additionally surface albedo and emission, we infer an absorbed solar and net thermal radiation of 137 and -67 Wm-2 over land, and of 170 and -53 Wm-2 over oceans. The surface net radiation thus amounts to around 70 Wm-2 over land and 117 Wm-2 over oceans, which may impose additional constraints on the respective sensible and latent heat fluxes.
We discuss further aspects of decadal changes in these fluxes, based on updated surface observations from the BSRN network, as well as their representation in CMIP5 models.
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