 |
| Titel |
divand-1.0: n-dimensional variational data analysis for ocean observations |
| VerfasserIn |
A. Barth, J.-M. Beckers, C. Troupin, A. Alvera-Azcárate, L. Vandenbulcke |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1991-959X
|
| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 1 ; Nr. 7, no. 1 (2014-01-29), S.225-241 |
| Datensatznummer |
250115539
|
| Publikation (Nr.) |
 copernicus.org/gmd-7-225-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
A tool for multidimensional variational analysis (divand) is
presented. It allows the interpolation and analysis of observations on
curvilinear orthogonal grids in an arbitrary high dimensional space by
minimizing a cost function. This cost function penalizes the deviation from
the observations, the deviation from a first guess and abruptly varying
fields based on a given correlation length (potentially varying in space and
time). Additional constraints can be added to this cost function such as an
advection constraint which forces the analysed field to align with the ocean
current. The method decouples naturally disconnected areas based on
topography and topology. This is useful in oceanography where disconnected
water masses often have different physical properties. Individual elements of
the a priori and a posteriori error covariance matrix can also be computed,
in particular expected error variances of the analysis. A multidimensional
approach (as opposed to stacking two-dimensional analysis) has the benefit of
providing a smooth analysis in all dimensions, although the computational
cost is increased.
Primal (problem solved in the grid space) and dual formulations (problem
solved in the observational space) are implemented using either direct
solvers (based on Cholesky factorization) or iterative solvers (conjugate
gradient method). In most applications the primal formulation with the direct
solver is the fastest, especially if an a posteriori error estimate is
needed. However, for correlated observation errors the dual formulation with
an iterative solver is more efficient.
The method is tested by using pseudo-observations from a global model. The
distribution of the observations is based on the position of the Argo floats.
The benefit of the three-dimensional analysis (longitude, latitude and time)
compared to two-dimensional analysis (longitude and latitude) and the role of
the advection constraint are highlighted. The tool divand is free
software, and is distributed under the terms of the General Public Licence (GPL)
(http://modb.oce.ulg.ac.be/mediawiki/index.php/divand). |
| |
|
| Teil von |
|
|
|
|
|
|
|
|