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| Titel |
The ASSET intercomparison of stratosphere and lower mesosphere humidity analyses |
| VerfasserIn |
H. E. Thornton, D. R. Jackson, S. Bekki, N. Bormann, Q. Errera, A. J. Geer, W. A. Lahoz, S. Rharmili |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 3 ; Nr. 9, no. 3 (2009-02-09), S.995-1016 |
| Datensatznummer |
250006826
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| Publikation (Nr.) |
 copernicus.org/acp-9-995-2009.pdf |
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| Zusammenfassung |
| This paper presents results from the first detailed intercomparison of
stratosphere-lower mesosphere water vapour analyses; it builds on earlier
results from the EU funded framework V "Assimilation of ENVISAT Data" (ASSET) project. Stratospheric
water vapour plays an important role in many key atmospheric processes and therefore
an improved understanding of its daily variability is desirable. With the
availability of high resolution, good quality Michelson Interferometer for
Passive Atmospheric Sounding (MIPAS) water vapour profiles, the ability of
four different atmospheric models to assimilate these data is tested. MIPAS
data have been assimilated over September 2003 into the models of the
European Centre for Medium Range Weather Forecasts (ECMWF), the Belgian
Institute for Space and Aeronomy (BIRA-IASB), the French Service d'Aéronomie
(SA-IPSL) and the UK Met Office. The resultant middle atmosphere humidity
analyses are compared against independent satellite data from the Halogen
Occultation Experiment (HALOE), the Polar Ozone and Aerosol Measurement (POAM
III) and the Stratospheric Aerosol and Gas Experiment (SAGE II). The MIPAS
water vapour profiles are generally well assimilated in the ECMWF, BIRA-IASB
and SA systems, producing stratosphere-mesosphere water vapour fields where
the main features compare favourably with the independent observations.
However, the models are less capable of assimilating the MIPAS data where
water vapour values are locally extreme or in regions of strong humidity
gradients, such as the southern hemisphere lower stratosphere polar vortex.
Differences in the analyses can be attributed to the choice of humidity
control variable, how the background error covariance matrix is generated,
the model resolution and its complexity, the degree of quality control of the
observations and the use of observations near the model boundaries. Due to
the poor performance of the Met Office analyses the results are not included
in the intercomparison, but are discussed separately. The Met Office results
highlight the pitfalls in humidity assimilation, and provide lessons that
should be learnt by developers of stratospheric humidity assimilation
systems. In particular, they underline the importance of the background error
covariances in generating a realistic troposphere to mesosphere water vapour
analysis. |
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