Evaluation Of Ensemble Forecasts By PECA
Mozheng Wei and Zoltan Toth
NCEP Environmental Modeling Center
A method called Perturbation vs. Error Correlation Analysis (PECA),
which evaluates the ensemble perturbations instead of the forecasts
themselves by measuring their ability to explain forecast error
is used to evaluate ensemble forecasts from NCEP and ECMWF. Ensemble
perturbations from NCEP and ECMWF were found to perform similarly.
The error variance explained by either ensemble increases with the
of members and the lead time. The dynamically conditioned NCEP and ECMWF
perturbations outperform both randomly chosen perturbations and
differences between lagged forecasts ("NMC" method). Thus ensemble
forecasts potentially could be used to construct flow dependent
forecast error covariance matrices for use in data assimilation schemes.