Adjoint-based forecast sensitivity applied to observation error variances tuning

TitleAdjoint-based forecast sensitivity applied to observation error variances tuning
Publication TypeMiscellaneous
Year of Publication2015
AuthorsLupu, C, Cardinali, C, McNally, A
Secondary TitleTechnical Memorandum
Date PublishedJune
Type of WorkTechnical Memorandum

This paper deals with the estimation of observation errors for Infrared Atmospheric Sounding Interferometer (IASI) radiances. We investigate the possibility of combining an established method based on diagnosing errors from innovation statistics (so called Desroziers method) with guidance obtained from adjoint sensitivity tools (that aim to minimise short-range forecast error). In a test version of the European Centre for Medium-range Weather Forecasts (ECMWF) 4D-Var assimilation system that uses in situ observations and IASI as the only source of satellite data, it is found that tuning the IASI observation errors with a combined approach is beneficial (compared to using the innovation based method alone). Fits to data within the analysis are improved and forecasts initiated from the retuned analyses also show a moderate increase in skill.