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Ensemble forecasting at NCEP and the breeding method (1997)
| Venue: | Mon. Wea. Rev |
| Citations: | 191 - 15 self |
BibTeX
@ARTICLE{Toth97ensembleforecasting,
author = {Zoltan Toth and Eugenia Kalnay},
title = {Ensemble forecasting at NCEP and the breeding method},
journal = {Mon. Wea. Rev},
year = {1997},
pages = {3297--3319}
}
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Abstract
The breeding method has been used to generate perturbations for ensemble forecasting at the National Centers for Environmental Prediction (formerly known as the National Meteorological Center) since December 1992. At that time a single breeding cycle with a pair of bred forecasts was implemented. In March 1994, the ensemble was expanded to seven independent breeding cycles on the Cray C90 supercomputer, and the forecasts were extended to 16 days. This provides 17 independent global forecasts valid for two weeks every day. For efficient ensemble forecasting, the initial perturbations to the control analysis should adequately sample the space of possible analysis errors. It is shown that the analysis cycle is like a breeding cycle: it acts as a nonlinear perturbation model upon the evolution of the real atmosphere. The perturbation (i.e., the analysis error), carried forward in the first-guess forecasts, is ‘‘scaled down’ ’ at regular intervals by the use of observations. Because of this, growing errors associated with the evolving state of the atmosphere develop within the analysis cycle and dominate subsequent forecast error growth. The breeding method simulates the development of growing errors in the analysis cycle. A difference field between two nonlinear forecasts is carried forward (and scaled down at regular intervals) upon the evolving atmospheric analysis fields. By construction, the bred vectors are superpositions of the leading local (timedependent)
Keyphrases
breeding method ensemble forecasting analysis cycle regular interval efficient ensemble forecasting national meteorological center subsequent forecast error growth breeding cycle single breeding cycle nonlinear perturbation model real atmosphere independent global forecast cray c90 supercomputer nonlinear forecast possible analysis error difference field national center bred vector environmental prediction atmospheric analysis field bred forecast first-guess forecast initial perturbation control analysis analysis error
