A consistent hybrid variational-smoothing data assimilation method: Application to a simple shallow-water model of the turbulent midlatitude ocean

Monika Krysta 1 Eric Blayo 1 Emmanuel Cosme 2 Jacques Verron 2
1 MOISE - Modelling, Observations, Identification for Environmental Sciences
Inria Grenoble - Rhône-Alpes, LJK - Laboratoire Jean Kuntzmann, INPG - Institut National Polytechnique de Grenoble
Abstract : In the standard four-dimensional variational data assimilation (4D-Var) algorithm the background error covariance matrix B remains static over time. It may therefore be unable to correctly take into account the information accumulated by a system into which data are gradually being assimilated. A possible method for remedying this flaw is presented and tested in this paper. A hybrid variational-smoothing algorithm is based on a reduced-rank incremental 4D-Var. Its consistent coupling to a singular evolutive extended Kalman (SEEK) smoother ensures the evolution of the B matrix. In the analysis step, a low-dimensional error covariance matrix is updated so as to take into account the increased confidence level in the state vector it describes, once the observations have been introduced into the system. In the forecast step, the basis spanning the corresponding control subspace is propagated via the tangent linear model. The hybrid method is implemented and tested in twin experiments employing a shallow-water model. The background error covariance matrix is initialized using an EOF decomposition of a sample of model states. The quality of the analyses and the information content in the bases spanning control subspaces are also assessed. Several numerical experiments are conducted that differ with regard to the initialization of the B matrix. The feasibility of the method is illustrated. Since improvement due to the hybrid method is not universal, configurations that benefit from employing it instead of the standard 4D-Var are described and an explanation of the possible reasons for this is proposed.
Type de document :
Article dans une revue
Monthly Weather Review, American Meteorological Society, 2011, 139 (11), pp.3333-3347. 〈10.1175/2011MWR3150.1〉
Liste complète des métadonnées

https://hal.inria.fr/hal-00769109
Contributeur : Eric Blayo <>
Soumis le : vendredi 28 décembre 2012 - 11:26:11
Dernière modification le : mercredi 11 avril 2018 - 01:58:15

Identifiants

Collections

Citation

Monika Krysta, Eric Blayo, Emmanuel Cosme, Jacques Verron. A consistent hybrid variational-smoothing data assimilation method: Application to a simple shallow-water model of the turbulent midlatitude ocean. Monthly Weather Review, American Meteorological Society, 2011, 139 (11), pp.3333-3347. 〈10.1175/2011MWR3150.1〉. 〈hal-00769109〉

Partager

Métriques

Consultations de la notice

370