The surface radiation budget and its representation in CMIP5 models

The genesis and evolution of Earth's climate is largely regulated by the Earth radiation balance. Despite of its key role in the context of climate change, substantial uncertainties still exist in the quantification of the magnitudes of its different components, and its representation in climate models. While the net radiative energy flow in and out of the climate system at the top of atmosphere is now known with considerable accuracy from satellite programs such as CERES, the energy distribution within the climate system and at the Earth surface is less well determined. Accordingly, the magnitudes of the components of the surface energy balance have recently been disputed and show largely varying values in climate models even on a global mean basis.

We made an attempt to further constrain the magnitudes of the surface radiative components with largest uncertainties, namely the surface downward solar and thermal fluxes. Complementary to the approaches using satellite-derived products as references we make extensive use of the growing number of surface observations to constrain the radiative components at the Earth's surface. These observations stem from the Global Energy Balance Archive (GEBA) and the Baseline Surface Radiation Network (BSRN). We combine these observations with the latest global modeling efforts performed within the Coupled Model Intercomparison Project Phase 5 (CMIP5) to infer best estimates for the global mean surface radiative components. A regression between the model calculated global mean fluxes and their respective biases compared to the surface observations suggests global mean values of downward surface solar and thermal radiation near 185 and 342 Wm^-2, respectively, to be most compatible with surface observations. It is encouraging that these estimates, which make full use of the information contained in the surface networks, coincide within 2 Wm^-2 with the latest satellite-derived estimates from CERES-EBAF (Kato et al. 2013), which are completely independently determined. Combined with an estimated global mean surface absorbed solar radiation and thermal emission of 161 Wm^-2 and 398 Wm^-2, respectively, this leaves around 105 Wm^-2 of surface net radiation globally available for the distribution amongst the non-radiative surface energy balance components. This may impose additional constraints on the global mean sensible and latent heat fluxes and associated hydrological cycle.

References

Kato, S., Loeb, N.G., Rose, F.G., Doelling, D.R., Rutan, D.A., Caldwell ,T.E., Yu, L., and Weller, R., 2013: Surface irradiances consistent with CERES-derived top-of-atmosphere shortwave and longwave irradiances. J. Clim. 26, 2719-2740

Wild, M., Folini, D., Schär, C., Loeb, N., Dutton, E.G., and König-Langlo, G., 2013: The global energy balance from a surface perspective, Clim. Dyn., 40, 3107-3134, Doi:10.1007/s00382-012-1569-8.

Wild, M., Folini, D., Schär, C., Loeb, N., Dutton, E.G., and König-Langlo, G., 2013: A new diagram of the global energy balance, AIP Conf. Proc., 1531, 628-631, doi: 10.1063/1.4804848.