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The ETKF rescaling scheme in HIRLAM Cover

The ETKF rescaling scheme in HIRLAM

Open Access
|Jan 2011

Abstract

The ETKF rescaling scheme has been implemented into the HIRLAM forecasting system in order to estimate the uncertainty of the model state. The main purpose is to utilize this uncertainty information for modelling of flowdependent background error covariances within the framework of a hybrid variational ensemble data assimilation scheme. The effects of rank-deficiency in the ETKF formulation is explained and the need for variance inflation as a way to compensate for these effects is justified. A filter spin-up algorithm is proposed as a refinement of the variance inflation. The proposed spin-up algorithm will also act to prevent ensemble collapse since the ensemble will receive ‘fresh blood’ in the form of additional perturbation components, generated on the basis of a static background error covariance matrix. The resulting ETKF-based ensemble perturbations are compared with ensemble perturbations based on targeted singular vectors and are shown to have more realistic spectral characteristics.

Language: English
Page range: 385 - 401
Submitted on: Jan 11, 2010
Accepted on: Jan 4, 2011
Published on: Jan 1, 2011
Published by: Stockholm University Press
In partnership with: Paradigm Publishing Services

© 2011 Jelena Bojarova, Nils Gustafsson, Åke Johansson, Ole Vignes, published by Stockholm University Press
This work is licensed under the Creative Commons Attribution 4.0 License.