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| Titel |
Optimization of vegetation model parameters through sequential assimilation of surface albedo observations |
| VerfasserIn |
Gernot Geppert, Alexander Loew |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250081522
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| Zusammenfassung |
| The dynamic global vegetation model JSBACH, which is the land component of the
MPIÂ Earth System Model, uses cover fractions of up to 21 plant functional types (PFT) to
represent the vegetation in a grid box. Each PFT is described by a set of parameters and the
global distribution of PFTs allows for a spatially differentiated description of the land surface.
The PFT parameters, however, are constant over time and thus neglect processes that lead to
seasonal changes of the described properties.
In the case of land surface albedo, this simplification leads to decreased seasonal
variability within model results compared to observations of the Moderate Resolution
Imaging Spectroradiometer (MODIS), because the fixed canopy albedo parameters of
JSBACH do not adequately represent the seasonal changes of the leaves’ radiative
properties.
To judge the seasonal variability of these parameters and to derive an appropriate
seasonally varying parameterization, we set up a flexible and extensible data assimilation
framework that allows to estimate a time series of parameter values. We incorporated a
standalone version of JSBACH forced by ERA-Interim reanalysis data into the Data
Assimilation Research Testbed (DART). Within DART, an Ensemble Kalman Filter is applied
to sequentially update an ensemble of model states and parameters as new observations
become available. To handle the non-Gaussian distributions of a bounded quantity like albedo
we use a Gaussian anamorphosis technique.
We performed perfect model experiments to show that the assimilation system is able to
retrieve seasonally varying parameters. The synthetic observations for these experiments are
generated in a control run of JSBACH with seasonally varying canopy albedo parameters.
They were perturbed to mimic observation error and subsequently used in an assimilation
run. The results of the assimilation were evaluated with respect to reproducing the parameters
of the control run. |
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