Coupled data assimilation at ECMWF: current status, challenges and future developments

Abstract This article presents coupled data assimilation (DA) activities at the European Centre for Medium‐Range Weather Forecasts (ECMWF). Coupled DA is an essential component of ECMWF Earth‐system strategy. It aims providing consistent initial conditions to atmosphere, land, and ocean forecast model. The introduces different systems observing each component. discusses challenges related observation consistency, availability, sustainability across components. gives a review coupling methodologies methods in development ECMWF. current system relies on weakly approaches between land wave atmosphere. Research has been centred outer loop developments evaluation, focused ocean–atmosphere reanalysis numerical weather prediction. latest configuration combines weak methods. assimilating surface‐sensitive observations it opportunities that offers enhance exploitation interface observations. recent land–atmosphere forward operator multilayer snow‐emission modelling shows potential radiative transfer low‐frequency passive microwave. ongoing in‐house sea‐surface temperature analysis based skin assimilation. preliminary results demonstrate meaningful upper increments when information from four‐dimensional variational are illustrated discussed context several applications reanalysis, scatterometer impact ocean–atmosphere, tropical cyclone, sea‐ice–atmosphere as well surface case studies. These examples illustrate benefits developments. future plans support ECMWF's 2021–2030