The impact of ASCAT winds in storm cases using the HARMONIE model system EUMETSAT Fellowship Programme: First year report

Abstract Scatterometer winds have a potential to improve forecasting of severe weather events byimproving the initial state of atmosphere through data assimilation. Within the EUMETSATfellowship project, Advanced Scatterometer (ASCAT) ocean surface wind data from MetOp-A and MetOp-B satellites are applied in the 3D-Var data assimilation system available inthe high-resolution HARMONIE model used at the Norwegian Meteorological Institute. TheASCAT wind data assimilation demonstrates a slight positive impact on forecasting meansea level pressure (MSLP) at the forecast lengths of 3-21 hours for a selected severe stormcase. Upper levels show a slight improvement on the 24-h forecast of wind speed at 850hPa, temperature at 700 hPa and specific humidity at 500 hPa. Other surface variables orthe upper atmosphere do not experience significant changes. The first attempt to optimisethe use of ASCAT data by reducing the thinning distance further improves the averageverification scores slightly for MSLP. The reduced thinning distance applied in a polar lowcase clearly improves the MSLP at the time of the polar low event, even though ASCATdata do not enhance the statistics averaged over the whole simulation period in this case.This limited set of experiments were cases where we found data assimilation of ASCAT tobe beneficial for forecasting of storms.