Validation of IFS+RTTOV/MFASIS solar reflectances against GOES-16 ABI obs

Solar reflectances simulated by running RTTOV/MFASIS (fast visible simulator) on input meteorological data from ECMWF’s operational IFS short-range forecasts are compared with corresponding GOES-16 ABI reflectances observed in channels 0.47, 0.64 and 0.86mm. This is the first systematic validation of the IFS at wavelengths in the solar spectrum, which is expected to provide additional information about the  prediction of meteorological features that are usually not well detected at infrared frequencies (e.g., low-level clouds). Month-long statistics of reflectances as well as individual images are used to identify deficiencies in both the IFS and in the RTTOV/MFASIS radiative transfer model. In the IFS, issues are found in the representation of trade-wind low-level clouds over ocean, shallow convection over the Amazon region and low-level clouds inside the eye of tropical cyclones. On the other hand, this study also confirms the existence of biases resulting from some of RTTOV/MFASIS’s simplifications, such as those made in the Rayleigh scattering computations and in the use of a look-up table. These conclusions are confirmed through an independent comparison of IFS with CERES observations. Results from this work are relevant to the developments towards the assimilation of solar reflectances in ECMWF’s 4-Dimensional Variational data assimilation system (4D-Var).