Progress towards assimilating cloud visible reflectances at ECMWF

Satellite observations are critical for numerical weather prediction (NWP), yet the full potential of visible spectral data remains to be explored. In recent years, ECMWF has been advancing efforts to incorporate visible satellite observations to enhance the analysis and forecasts of clouds and aerosols in the Integrated Forecasting System (IFS). We discuss results from the CLOVIS-2 and CERTAINTY projects, presenting visible reflectance (655 nm) monitoring and assimilation experiments using observations from the Ocean and Land Color Instrument (OLCI) onboard ESA's Sentinel 3A and 3B satellite missions. Our study assesses the first-ever successful experimental assimilation of visible all-sky satellite observations in the IFS using model CY49R1, which became operational in November 2024. A comprehensive evaluation of these experiments demonstrates that visible reflectance assimilation can improve the model analysis of clouds by better fitting the model trajectory to observations in reflectance space. We will also discuss the remaining challenges related to the future operational assimilation of visible observations, including observation operator refinements, observation error modelling, and the role of model errors and biases. Our findings underscore the vast potential of visible spectral data for operational NWP and future re-analysis products.