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| Titel |
Tropospheric profiles of wet refractivity and humidity from the combination of remote sensing data sets and measurements on the ground |
| VerfasserIn |
F. Hurter, O. Maier |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 11 ; Nr. 6, no. 11 (2013-11-14), S.3083-3098 |
| Datensatznummer |
250085107
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| Publikation (Nr.) |
 copernicus.org/amt-6-3083-2013.pdf |
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| Zusammenfassung |
We reconstruct atmospheric wet refractivity profiles for the western
part of Switzerland with a least-squares collocation approach from
data sets of (a) zenith path delays that are a byproduct of the GPS
(global positioning system) processing, (b) ground meteorological
measurements, (c) wet refractivity profiles from radio occultations
whose tangent points lie within the study area, and (d) radiosonde
measurements. Wet refractivity is a parameter partly describing the
propagation of electromagnetic waves and depends on the atmospheric
parameters temperature and water vapour pressure. In addition, we have
measurements of a lower V-band microwave radiometer at Payerne. It
delivers temperature profiles at high temporal resolution, especially
in the range from ground to 3000 m a.g.l., though vertical
information content decreases with height. The temperature profiles
together with the collocated wet refractivity profiles provide
near-continuous dew point temperature or relative humidity profiles at
Payerne for the study period from 2009 to 2011.
In the validation of the humidity profiles, we adopt a two-step
procedure. We first investigate the reconstruction quality of
the wet refractivity profiles at the location of Payerne by
comparing them to wet refractivity profiles computed from
radiosonde profiles available for that location. We also assess
the individual contributions of the data sets to the
reconstruction quality and demonstrate a clear benefit from the
data combination. Secondly, the accuracy of the conversion from
wet refractivity to dew point temperature and relative humidity
profiles with the radiometer temperature profiles is examined,
comparing them also to radiosonde profiles.
For the least-squares collocation solution combining GPS and ground
meteorological measurements, we achieve the following error figures
with respect to the radiosonde reference: maximum median offset of
relative refractivity error is −16% and quartiles are 5% to
40% for the lower troposphere. We further added 189
radio occultations that met our requirements. They mostly improved the
accuracy in the upper troposphere. Maximum median offsets have
decreased from 120% relative error to 44% at 8 km height. Dew
point temperature profiles after the conversion with radiometer
temperatures compare to radiosonde profiles as to: absolute dew point
temperature errors in the lower troposphere have a maximum median
offset of −2 K and maximum quartiles of 4.5 K. For relative
humidity, we get a maximum mean offset of 7.3%, with standard
deviations of 12–20%.
The methodology presented allows us to reconstruct humidity
profiles at any location where temperature profiles, but no
atmospheric humidity measurements other than from GPS are
available. Additional data sets of wet refractivity are shown to
be easily integrated into the framework and strongly aid the
reconstruction. Since the used data sets are all operational and
available in near-realtime, we envisage the methodology of this
paper to be a tool for nowcasting of clouds and rain
and to understand processes in the boundary layer and at its
top. |
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