How Well Operational Ensembles Can Explain Forecast Errors?
Tuesday, April 30, 2002 - 9:00am - 9:45am
Zoltan Toth (National Oceanographic and Atmospheric Administration (NOAA))
Ensemble based schemes have shown great promise in data assimilation experiments in simple and moderately complex environments. Potentially, ensembles can provide and propagate in time case dependent forecast error covariance information in advanced data assimilation schemes. In this talk the ability of the operational NCEP and ECMWF ensembles to explain forecast error fields will be examined in a realistic, imperfect model environment. The performance of randomly chosen perturbations, lagged forecast differences (the NMC method), as well as perfect ensemble perturbations will be contrasted with the performance of the operational ensemble systems. The results indicate that the current operational ensembles do not provide enough diversity in perturbation patterns that would allow for the proper explanation of forecast errors. Even if the ensemble information is used on a regional basis, (1) a relatively large, (2) more diverse ensemble, that can (3) better account for model related errors will be required for successful applications of ensembles in data assimilation schemes.