Diurnal Asymmetry in the GERB SW Fluxes

The launch of the Geostationary Earth Radiation Budget (GERB) instrument onboard the Meteostat 8 allows a diurnal sampling of the Earth´s Radiation Budget for the first time, providing a unique and important addition to polar-orbiting measurements. However, preliminary data from the GERB instrument exhibit systematic asymmetry in the short-wave (SW) flux diurnal variation. Such asymmetries are not found in the Clouds and the Earth´s Radiant Energy System angular distribution models used to convert the directional broad-band GERB SW radiances to fluxes. Comparison between angularly matched estimations of reflected SW flux at the top of the atmosphere from the Spinning Enhanced Visible and Infra Red Imager (SEVIRI) and GERB data indicates that the SEVIRI spectral modeling could be a major issue. In addition, the results indicate that other factors such as the GERB SW geolocation, the GERB detector spectral response functions, the GERB nominal footprint resolution, and cloud cover could also potentially have an influence on the diurnal evolution of the GERB SW fluxes, as they can erroneously impact on the GERB SW correction factor