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Comparison of strategies for the specification of anisotropies in the covariances of a three-dimensional atmospheric data assimilation system
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2006
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Description:Spatial recursive filters and the Hexad algorithm are used to implement four different models of anisotropic background error covariances within the NCEP Eta 3DVAR system.The covariance models are based on the Riishøjgaard method, the semigeostrophic and semigeostrophic-isentropic transformation methods, and the so-called kinematic deformation method. Each formulation uses background state diagnostics to define a distinct local aspect tensor of the assumed Gaussian correlation models.The forecast impacts of the various formulations are evaluated from simulations of a 2004 late winter storm over the continental U.S. All four covariance models used in the case study are found to have a significant, positive impact on the forecast skill measured in terms of the mean-squared errors of the 500 hPa geopotential height and the precipitation equitable threat scores.
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Content Notes:Manuel S.F.V. De Pondeca, R. James Purser, David F. Parrish, and John C. Derber.
"September 2006."
"This is an unreviewed manuscript, primarily intended for informal exchange of information among the NCEP staff members."
System requirements: Adobe Acrobat Reader.
Includes bibliographical references (page 13).
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Rights Information:Public Domain
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Compliance:Library
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