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Two alternative implementations of the ensemble‐transform (ET) analysis‐perturbation scheme: The ET with extended cycling intervals, and the ET without cycling
Author(s) -
McLay Justin,
Reynolds Carolyn A.
Publication year - 2009
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.437
Subject(s) - covariance , mathematics , perturbation (astronomy) , basis (linear algebra) , diagonal , eigenvalues and eigenvectors , ensemble average , variance (accounting) , covariance matrix , statistics , climatology , physics , geometry , accounting , quantum mechanics , business , geology
Four alternative approximate bases for the ensemble transform (ET) are obtained by extending the cycling interval to 24, 48, 72 and 96 h. Another alternative basis is obtained by foregoing cycling and instead drawing randomly generated perturbations from an archive. Experiments based upon 16‐member global ensembles and a diagonal estimate of analysis‐error covariance indicate that the alternative bases are effective at reducing the discrepancy between the ET analysis‐perturbation variance and the estimated analysis‐error variance. Forecast ensembles associated with the alternative bases maintain considerably more energy in the tropics and subtropics than the forecast ensemble associated with the original basis. Forecast ensembles associated with the alternative bases also outperform the original forecast ensemble in terms of the ensemble forecast‐error covariance‐matrix eigenvalue spectrum, the relationship between ensemble variance and observed squared error and the Brier score. The performance gains facilitated by the alternative approximate bases are substantial in some instances, especially in the tropics. The randomly sampled basis is superior to the original basis in most respects. Published in 2009 by John Wiley & Sons, Ltd.