Unpublished conference/Abstract (Scientific congresses and symposiums)
Local ensemble assimilation scheme with global constraints and conservation
Barth, Alexander; Yan, Yajing; Canter, Martin et al.
2015The 47th International Liege Colloquium
 

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Keywords :
data assimilation; conservation
Abstract :
[en] Ensemble assimilation schemes applied in their original, global formulation have no problem in respecting linear conservation properties if the ensemble perturbations are setup accordingly. For realistic ocean systems, only a relatively small number of ensemble members can be calculated. A localization of the ensemble increment is thus necessary to filter out spurious long-range correlations. However, the conservation of the global property will be lost if the assimilation is performed locally since the conservation requires a coupling between model grid points, which is filtered out by the localization. In the ocean, the distribution of observations is highly inhomogeneous. System- atic errors of the observed parts of the ocean state can lead to spurious systematic adjust- ments of the non-observed part of the ocean state due to data assimilation. As a result, global properties which should be conserved, increase or decrease in long-term simulations. We propose an assimilation scheme (with stochastic or deterministic analysis steps) which is formulated globally (i.e. for the whole state vector) but where spurious long-range correlations can be filtered out. The scheme can thus be used to enforce global conservation properties and non-local observation operators. Both aspects are indeed linked since one can introduce the global conservation as a weak constraint by using a global ob- servation operator. The conserved property becomes thus an observed value. The proposed scheme is tested with the Kuramoto-Sivashinsky model which is conservative. The benefit compared to the traditional covariance localization scheme (with an ad-hoc step enforcing conservation) where observations are assimilated sequentially is shown. The assimilation scheme is suitable to be implemented on parallel computers where the number of available computing cores is a multiple of the ensemble size.
Research center :
GeoHydrodynamics and Environment Research
Disciplines :
Earth sciences & physical geography
Author, co-author :
Barth, Alexander  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Yan, Yajing ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Canter, Martin ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Alvera Azcarate, Aïda  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Beckers, Jean-Marie  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Language :
English
Title :
Local ensemble assimilation scheme with global constraints and conservation
Publication date :
2015
Event name :
The 47th International Liege Colloquium
Event date :
4-8 May 2015
By request :
Yes
European Projects :
FP7 - 283580 - SANGOMA - Stochastic Assimilation for the Next Generation Ocean Model Applications
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
UE - Union Européenne [BE]
CE - Commission Européenne [BE]
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since 12 February 2016

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