Carla Cardinali, ECMWF

Abstract: Over the last decade data assimilation schemes have evolved towards very sophisticated systems. The scheme handles a large variety of both space and surface-based meteorological observations. It combines the observations with prior (or background) information on the atmospheric state and uses a comprehensive (linearized) forecast model to ensure that the observations are given a dynamically and statistically realistic response in the analysis. Effective performance monitoring of such a complex system, with an order of 109 degrees of freedom and more than 107 observations per 12-hour assimilation cycle has become an absolute necess ity. The assessment of each observation contribution to the analysis and forecast is among the most challenging diagnostics in data assimilation and numerical weather prediction. Recently, adjoint-based observation sensitivity techniques have been used to measure the observation contribution to the forecast, where the observation impact is evaluated with respect to a scalar function representing the short-range forecast error. Moreover, the theoretical framework to evaluate the other analysis input parameters impact, not only the observation impact, has been derived and application will be shown. The performance of the current ECMWF operational version of the data assimilation and forecast system for June 2010 shows a consistent overall positive impact of the observations. In particular, a comprehensive assessment of the impact of GPS radio occultation observations and all-sky microwave imager radiances in the assimilation and forecast system is in this talk provided, throughout the diagnostic tools introduced above.