Journal article

Adaptive Ensemble Covariance Localization in Ensemble 4D-VAR State Estimation

Craig H Bishop, Daniel Hodyss

MONTHLY WEATHER REVIEW | AMER METEOROLOGICAL SOC | Published : 2011

Abstract

An adaptive ensemble covariance localization technique, previously used in "local" forms of the ensemble Kalman filter, is extended to a global ensemble four-dimensional variational data assimilation (4D-VAR) scheme. The purely adaptive part of the localization matrix considered is given by the element-wise square of the correlation matrix of a smoothed ensemble of streamfunction perturbations. It is found that these purely adaptive localization functions have spurious far-field correlations as large as 0.1 with a 128-member ensemble. To attenuate the spurious features of the purely adaptive localization functions, the authors multiply the adaptive localization functions with very broadscale..

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University of Melbourne Researchers