Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 2 4 2002 10.5194/acpd-2-921-2002 http://www.atmos-chem-phys-discuss.net/2/921/2002/ http://www.atmos-chem-phys-discuss.net/2/921/2002/acpd-2-921-2002.html http://www.atmos-chem-phys-discuss.net/2/921/2002/acpd-2-921-2002.pdf 921 942 2002-07-10 Global ozone forecasting based on ERS-2 GOME observations H. J. Eskes P. F. J. van Velthoven, H. M. Kelder Royal Netherlands Meteorological Institute, De Bilt, The Netherlands The availability of near-real time ozone observations from satellite instruments has recently initiated the development of ozone data assimilation systems. In this paper we present the results of an ozone assimilation and forecasting system, in use since Autumn 2000. The forecasts are produced by an ozone transport and chemistry model, driven by the operational medium range forecasts of ECMWF. The forecasts are initialised with realistic ozone distributions, obtained by the assimilation of near-real time total column observations of the GOME spectrometer on ERS-2. The forecast error diagnostics demonstrate that the system produces meaningful total ozone forecasts for up to 6 days in the extratropics. In the tropics meaningful forecasts of the small anomalies are restricted to shorter periods of about two days with the present model setup. It is demonstrated that important events, such as the breakup of the South Pole ozone hole and mini-hole events above Europe can be successfully predicted 4--5 days in advance.