Radiation and Surface Energy Budgets in Climate Models
Substantial differences exist in the representation of radiation and surface energy fluxes in climate models. We use comprehensive sets of worldwide distributed surface flux measurements combined with satellite measurements to evaluate and constrain the energy fluxes in climate models. The GEBA database provides a useful source of information for these studies. We also address related methodological aspects, such as the quantification of the error introduced by the spatial mismatch between the point observations at the surface and the larger scale of the gridded climate model data (Hakuba et al. 2013, 2014, Schwarz et al. 2017). Our studies over several generations of climate models show that globally climate models tend to overestimate the solar radiation and underestimate the thermal radiation incident at the surface (e.g., Wild et al. 1995, 1998, 2015, Wild 2008). This results in a globally realistic surface radiation balance due to error cancellation in the solar and thermal fluxes. This error cancellation, however, does no longer apply on regional, seasonal and diurnal spatial and temporal scales, inducing substantial errors in the simulation of the thermal and hydrological conditions at the Earth surface which crucially depend on an accurate surface radiation balance. Substantial uncertainties also exist in the radiation budgets under cloud-fre conditions, thus not considering the uncertainties induced by the simulation of clouds. We also make an attempt to constrain these fluxes in models using newly established observational clear-sky reference data (Wild et al. 2006, 2018).