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| Titel |
The STARTWAVE atmospheric water database |
| VerfasserIn |
J. Morland, B. Deuber, D. G. Feist, L. Martin, S. Nyeki, N. Kämpfer, C. Mätzler, P. Jeannet, L. Vuilleumier |
| 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 ; 6, no. 8 ; Nr. 6, no. 8 (2006-06-20), S.2039-2056 |
| Datensatznummer |
250003918
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| Publikation (Nr.) |
 copernicus.org/acp-6-2039-2006.pdf |
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| Zusammenfassung |
| The STARTWAVE (STudies in Atmospheric Radiative Transfer and Water Vapour
Effects) project aims to investigate the role which water vapour plays in
the climate system, and in particular its interaction with radiation. Within
this framework, an ongoing water vapour database project was set up which
comprises integrated water vapour (IWV) measurements made over the last ten
years by ground-based microwave radiometers, Global Positioning System (GPS)
receivers and sun photometers located throughout Switzerland at altitudes
between 330 and 3584 m. At Bern (46.95° N, 7.44° E) tropospheric and
stratospheric water vapour profiles are obtained on a regular basis and
integrated liquid water, which is important for cloud characterisation, is
also measured. Additional stratospheric water vapour profiles are obtained
by an airborne microwave radiometer which observes large parts of the
northern hemisphere during yearly flight campaigns. The database allows us
to validate the various water vapour measurement techniques. Comparisons
between IWV measured by the Payerne radiosonde with that measured at Bern by
two microwave radiometers, GPS and sun photometer showed instrument biases
within ±0.5 mm. The bias in GPS relative to sun photometer over the
2001 to 2004 period was –0.8 mm at Payerne (46.81° N, 6.94° E, 490 m), which
lies in the Swiss plains north of the Alps, and +0.6 mm at Davos (46.81° N,
9.84° E, 1598 m), which is located within the Alps in the eastern part of
Switzerland. At Locarno (46.18° N, 8.78° E, 366 m), which is located on the
south side of the Alps, the bias is +1.9 mm. The sun photometer at Locarno
was found to have a bias of –2.2 mm (13% of the mean annual IWV) relative to the data from the closest radiosonde station at Milano. This
result led to a yearly rotation of the sun photometer instruments between
low and high altitude stations to improve the calibrations. In order to
demonstrate the capabilites of the database for studying water vapour
variations, we investigated a front which crossed Switzerland between
18 November 2004 and 19 November 2004. During the frontal passage, the GPS and microwave
radiometers at Bern and Payerne showed an increase in IWV of between 7 and 9 mm. The
GPS IWV measurements were corrected to a standard height of 500 m, using an
empirically derived exponential relationship between IWV and altitude. A
qualitative comparison was made between plots of the IWV distribution
measured by the GPS and the 6.2 µm water vapour channel on the Meteosat
Second Generation (MSG) satellite. Both showed that the moist air moved in
from a northerly direction, although the MSG showed an increase in water
vapour several hours before increases in IWV were detected by GPS or
microwave radiometer. This is probably due to the fact that the satellite
instrument is sensitive to an atmospheric layer at around 320 hPa, which
makes a contribution of one percent or less to the IWV. |
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