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| Titel |
Spatiotemporal variability of water vapor investigated using lidar and FTIR vertical soundings above the Zugspitze |
| VerfasserIn |
H. Vogelmann, R. Sussmann, T. Trickl, A. Reichert |
| 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 ; 15, no. 6 ; Nr. 15, no. 6 (2015-03-19), S.3135-3148 |
| Datensatznummer |
250119564
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| Publikation (Nr.) |
 copernicus.org/acp-15-3135-2015.pdf |
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| Zusammenfassung |
| Water vapor is the most important greenhouse gas and its spatiotemporal
variability strongly exceeds that of all other greenhouse gases. However,
this variability has hardly been studied quantitatively so far. We present an
analysis of a 5-year period of water vapor measurements in the free
troposphere above the Zugspitze (2962 m a.s.l., Germany). Our results are
obtained from a combination of measurements of vertically integrated water vapor
(IWV), recorded with a solar Fourier transform infrared (FTIR) spectrometer on
the summit of the Zugspitze and of water vapor profiles recorded with the nearby
differential absorption lidar (DIAL) at the Schneefernerhaus research station.
The special geometrical arrangement of one zenith-viewing and one sun-pointing
instrument and the temporal resolution of both instruments allow for an
investigation of the spatiotemporal variability of IWV on a spatial scale of
less than 1 km and on a timescale of less than 1 h. The standard
deviation of differences between both instruments σIWV calculated for varied
subsets of data serves as a measure of variability. The different subsets are
based on various spatial and temporal matching criteria. Within a time interval
of 20 min, the spatial variability becomes significant for horizontal
distances above 2 km, but only in the warm season (σIWV =0.35 mm).
However, it is not sensitive to the horizontal distance during the winter season. The
variability of IWV within a time interval of 30 min peaks in July and August
(σIWV > 0.55 mm, mean horizontal distance = 2.5 km) and has its minimum around
midwinter (σIWV < 0.2 mm, mean distance > 5 km). The temporal variability of IWV
is derived by selecting subsets of data from both instruments with optimal
volume matching. For a short time interval of 5 min, the variability is
0.05 mm and increases to more than 0.5 mm for a time interval of 15 h. The
profile variability of water vapor is determined by analyzing subsets of water
vapor profiles recorded by the DIAL within time intervals from 1 to 5 h. For
all altitudes, the variability increases with widened time intervals. The lowest
relative variability is observed in the lower free troposphere around an
altitude of 4.5 km. Above 5 km, the relative variability increases continuously
up to the tropopause by about a factor of 3. Analysis of the covariance of the
vertical variability reveals an enhanced variability of water vapor in the upper
troposphere above 6 km. It is attributed to a more coherent flow of
heterogeneous air masses, while the variability at lower altitudes is also
driven by local atmospheric dynamics. By studying the short-term variability of
vertical water vapor profiles recorded within a day, we come to the conclusion
that the contribution of long-range transport and the advection of heterogeneous
layer structures may exceed the impact of local convection by 1 order of
magnitude even in the altitude range between 3 and 5 km. |
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