Continuous data assimilation for the IFS

Lean, Peter ; Bonavita, Massimo ; Hólm, Elías ; Bormann, Niels ; McNally, Tony

Année de publication
2019

Accurate weather predictions are not possible without an accurate specification of the initial state of the Earth system. To this end, billions of observations of the Earth system are made every day. Data assimilation combines many of those observations with model information to arrive at a full set of initial conditions called the analysis. In the current ECMWF operational configuration, by the time the analysis is complete, the most recent observations that have gone into producing it are almost two hours old. This article presents a revised configuration of ECMWF's 4D-Var data assimilation system designed to allow the analysis to benefit from more recent observations. In the new, more continuous framework, we are able to assimilate observations arriving around one and half hours later than in the current system. In addition, more accurate albeit more time-consuming data assimilation configurations can be accommodated inside the operational schedule, providing scope for further improvements in analysis and forecast skill in upcoming cycles. The new data assimilation configuration has been found to improve forecast quality significantly. It is due to be implemented in the next upgrade of ECMWF's Integrated Forecasting System (IFS Cycle 46r1), scheduled for 2019.

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