European Centre for Medium-Range Weather Forecasts

Literary and scientific copyrights belong to ECMWF and are reserved in all countries. This publication is not to be reprinted or translated in whole or in part without the written permission of the Director. Appropriate non-commercial use will normally be granted under the condition that reference is made to ECMWF. The information within this publication is given in good faith and considered to be true, but ECMWF accepts no liability for error, omission and for loss or damage arising from its use. GEMS data assimilation system for chemically reactive gases A data assimilation system for chemically reactive gases has been developed at the European Centre for Medium-Range Weather Forecasts (ECMWF) for the ”Global and regional Earth-system Monitoring using Satellite and in-situ data ” (GEMS) project. ECMWF’s integrated forecast system (IFS) was extended to include the chemically reactive gases ozone, carbon monoxide, nitrogen oxides, formaldehyde and sulphur dioxide. Chemical transport models were coupled to the IFS using the OASIS4 coupler to model the chem-ical processes and to provide the IFS with chemical production and loss rates. This paper describes the assimilation system for the reactive gases, presents the background error statistics developed for the reactive gases, and shows some first results of the assimilation of satellite retrievals for all five new species.