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| Titel |
Mesoscale modelling of water vapour in the tropical UTLS: two case studies from the HIBISCUS campaign |
| VerfasserIn |
V. Marecal, G. Durry, K. Longo, S. Freitas, E. D. Rivière, M. Pirre |
| 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 ; 7, no. 5 ; Nr. 7, no. 5 (2007-03-19), S.1471-1489 |
| Datensatznummer |
250004758
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| Publikation (Nr.) |
 copernicus.org/acp-7-1471-2007.pdf |
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| Zusammenfassung |
In this study, we evaluate the ability of the BRAMS (Brazilian Regional
Atmospheric Modeling System) mesoscale model compared to ECMWF global
analysis to simulate the observed vertical variations of water vapour in the
tropical upper troposphere and lower stratosphere (UTLS). The observations
are balloon-borne measurements of water vapour mixing ratio and temperature
from micro-SDLA (Tunable Diode Laser Spectrometer) instrument. Data from two
balloon flights performed during the 2004 HIBISCUS field campaign are used
to compare with the mesoscale simulations and to the ECMWF analysis.
The observations exhibit fine scale vertical structures of water vapour of a
few hundred meters height. The ECMWF vertical resolution (~1 km) is too
coarse to capture these vertical structures in the UTLS. With a vertical
resolution similar to ECMWF, the mesoscale model performs better than ECMWF
analysis for water vapour in the upper troposphere and similarly or slightly
worse for temperature. The BRAMS model with 250 m vertical resolution is
able to capture more of the observed fine scale vertical variations of water
vapour compared to runs with a coarser vertical resolution. This is mainly
related to: (i) the enhanced vertical resolution in the UTLS and (ii) to the
more detailed microphysical parameterization providing ice supersaturations
as in the observations. In near saturated or supersaturated layers, the
mesoscale model predicted relative humidity with respect to ice saturation
is close to observations provided that the temperature profile is realistic.
For temperature, the ECMWF analysis gives good results partly attributed to
data assimilation. The analysis of the mesoscale model results showed that
the vertical variations of the water vapour profile depends on the dynamics
in unsaturated layer while the microphysical processes play a major role in
saturated/supersaturated layers.
In the lower stratosphere, the ECMWF model and the BRAMS model give very
similar water vapour profiles that are significantly drier than micro-SDLA
measurements. This similarity comes from the fact that BRAMS is initialised
using ECMWF analysis and that no mesoscale process acts in the stratosphere
leading to no modification of the BRAMS results with respect to ECMWF
analysis. |
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