Constraining Radiative Fluxes in the Climate System using Worldwide Surface Radiation Observations

The radiative energy exchanges between Sun, Earth and space can be accurately quantified from new satellite missions such as CERES or SORCE. However, the magnitudes of the radiative fluxes within the climate system and at the Earth surface, which cannot be directly measured by satellites, are afflicted with much larger uncertainties. Accordingly, also state of the art climate models show substantial discrepancies particularly in their surface radiative fluxes already on a global mean basis, which further accentuate on regional and seasonal scales (Wild et al. 2015, Wild 2017). In addition to satellite observations, a growing number of worldwide distributed surface observations can be used to better constrain the radiative fluxes not only from space, but also from the surface. Such observations become increasingly available for example through the Baseline Surface Radiation Network (BSRN) and the Global Energy Balance Archive (GEBA, Wild et al. 2017).

In my presentation, I will give an overview over recent research aiming at constraining radiative fluxes in the climate system and their representation in models, both in terms of their magnitudes as well as their decadal changes, based on the information contained in the surface observations. Recent advances have been achieved with the establishment of clear-sky flux climatologies from surface radiation records with sufficiently high temporal resolution (minutes up to daily) to allow for the differentiation between cloudy and cloud-free periods. The clear-sky flux climatologies are shown to be of use to constrain the global energy balance under cloud-free conditions, which may serve as a base state to infer the magnitude of cloud radiative effects not only at the Top of Atmosphere, but also within the atmosphere and at the Earth's surface. The clear-sky records further allow the differentiation between trends in surface radiative fluxes under cloudy and cloud-free conditions. A prerequisite is thereby that the underlying records are homogeneous, as shown for long-term records from China and Italy. Assessments of trends in surface solar radiation under both all-sky and clear-sky conditions may be able to provide more insights into the relative importance of clouds and aerosols for the explanation of their multidecadal variations known as “global dimming and brightening” (Wild 2012, 2016).

References

Wild, M. 2012: Enlightening Global Dimming and Brightening. Bull. Amer. Meteor. Soc., 93, 27–37, doi:10.1175/BAMS-D-11-00074.1

Wild, M., Folini, D., Hakuba, M., Schär, C., Seneviratne, S.I., Kato, S., Rutan, D., Ammann, C., Wood, E.F., and König-Langlo, G., 2015: The energy balance over land and oceans: An assessment based on direct observations and CMIP5 climate models. Clim. Dyn., 44, 3393–3429, doi: 10.1007/s00382-014-2430-z.

Wild, M., 2016: Decadal changes in radiative fluxes at land and ocean surfaces and their relevance for global warming, WIRES Clim Change, 7, 91–107, doi: 10.1002/wcc.372.

Wild, M., 2017: Towards Global Estimates of the Surface Energy Budget, Curr. Clim. Change Rep., 3, 87–97. doi: 10.1007/s40641-017-0058-x

Wild, M., Ohmura, A., Schär, C., Müller, G., Folini, D., Schwarz, M., Hakuba, M. Z., and Sanchez-Lorenzo, A., 2017: The Global Energy Balance Archive (GEBA) version 2017: a database for worldwide measured surface energy fluxes, Earth Syst. Sci. Data, 9, 601-613, doi: 10.5194/essd-9-601-2017.