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| Titel |
Assimilation of OMI NO2 retrievals into the limited-area chemistry-transport model DEHM (V2009.0) with a 3-D OI algorithm |
| VerfasserIn |
J. D. Silver, J. Brandt, M. Hvidberg, J. Frydendall, J. H. Christensen |
| 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 ; 6, no. 1 ; Nr. 6, no. 1 (2013-01-04), S.1-16 |
| Datensatznummer |
250003388
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| Publikation (Nr.) |
 copernicus.org/gmd-6-1-2013.pdf |
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| Zusammenfassung |
Data assimilation is the process of combining real-world
observations with a modelled geophysical field. The increasing
abundance of satellite retrievals of atmospheric trace gases makes
chemical data assimilation an increasingly viable method for
deriving more accurate analysed fields and initial conditions for
air quality forecasts.
We implemented a three-dimensional optimal interpolation (OI) scheme
to assimilate retrievals of NO2 tropospheric columns from
the Ozone Monitoring Instrument into the Danish Eulerian Hemispheric
Model (DEHM, version V2009.0), a three-dimensional, regional-scale,
offline chemistry-transport model. The background error covariance
matrix, B, was estimated based on differences in the
NO2 concentration field between paired simulations using
different meteorological inputs. Background error correlations were
modelled as non-separable, horizontally homogeneous and
isotropic. Parameters were estimated for each month and for each
hour to allow for seasonal and diurnal patterns in NO2
concentrations.
Three experiments were run to compare the effects of observation
thinning and the choice of observation errors. Model performance was
assessed by comparing the analysed fields to an independent set of
observations: ground-based measurements from European air-quality
monitoring stations. The analysed NO2 and O3
concentrations were more accurate than those from a reference
simulation without assimilation, with increased temporal correlation
for both species. Thinning of satellite data and the use of constant
observation errors yielded a better balance between the observed
increments and the prescribed error covariances, with no appreciable
degradation in the surface concentrations due to the observation
thinning. Forecasts were also considered and these showed rather
limited influence from the initial conditions once the effects of
the diurnal cycle are accounted for.
The simple OI scheme was effective and computationally feasible in
this context, where only a single species was assimilated, adjusting
the three-dimensional field for this compound. Limitations of the
assimilation scheme are discussed. |
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