The research described in this paper is an outgrowth of earlier experiments carried out by Jun Du (SAIC at EMC), in collaboration with the second author. The authors had stimulating discussions with Roberto Buizza (ECMWF), Peter Houtekamer (CMC Environment Canada), and Jeff Anderson (NCAR) prior to, and with Istvan Szunyogh (University of Maryland) and John Derber (EMC) during, the research. It is a pleasure to thank Yuejian Zhu and Richard Wobus for their technical help. The authors are grateful to David Burridge, director, and the staff of ECMWF, in particular Horst Boettger and John Hennessy, for participating in an exchange of ensemble forecast data between ECMWF and NCEP. We would also like to thank Kenneth Campana, Glenn White from NCEP, and three anonymous reviewers for comments on an early version of this paper.
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