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| Titel |
Study of the Jacobian of an extended Kalman filter for soil analysis in SURFEXv5 |
| VerfasserIn |
A. Duerinckx, R. Hamdi, J.-F. Mahfouf, P. Termonia |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 3 ; Nr. 8, no. 3 (2015-03-27), S.845-863 |
| Datensatznummer |
250116191
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| Publikation (Nr.) |
 copernicus.org/gmd-8-845-2015.pdf |
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| Zusammenfassung |
| An externalised surface scheme like SURFEX allows computationally
cheap offline runs. This is a major advantage for surface
assimilation techniques such as the extended Kalman filter (EKF),
where the offline runs allow a cheaper numerical estimation
of the observation operator Jacobian. In the recent past an EKF has
been developed within SURFEX for the initialisation of soil water
content and soil temperature based on screen-level temperature and
relative humidity observations. In this paper we make a comparison
of the Jacobian calculated with offline SURFEX runs and
with runs coupled to the atmospheric ALARO model. Comparisons are
made with respect to spatial structure and average value of the
Jacobian, gain values and increments. We determine the optimal
perturbation size of the Jacobian for the offline and
coupled approaches and compare the linearity of the Jacobian for
these cases. Results show that the offline Jacobian
approach gives similar results to the coupled approach and that it allows
for smaller perturbation sizes that better approximate this
linearity assumption. We document a new case of non-linearities
that can hamper this linearity assumption and cause spurious
2Δ t oscillations in small parts of the domain for the
coupled as well as offline runs. While these
oscillations do not have a detrimental effect on the model run, they
can introduce some noise in the Jacobian at the affected
locations. The oscillations influence both the surface fluxes and
the screen-level variables. The oscillations occur in the late
afternoon in summer when a stable boundary layer starts to form near
the surface. We propose a filter to remove the oscillations and show
that this filter works accordingly. |
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