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| Titel |
Footprint under low wind conditions |
| VerfasserIn |
Irene Lehner, Ivo Peter, Natascha Kljun |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054182
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| Zusammenfassung |
| Footprints give information about the upwind sources of point measurement at a flux tower.
This knowledge is of special interest as surface characteristics within the footprint influence
strongly the measured surface-atmosphere exchange and constitute a tool to evaluate fetch
quality and to interpret flux data. The footprint depends on atmospheric stability, surface
roughness, and measurement level. A number of approaches exist to predict the footprint.
Here we use the parametrised version of the Lagrangian stochastic dispersion LPDM-B
model (Kljun et al. 2004) which has the advantage of being valid for a wide range
of atmospheric conditions and simple to apply for long-term measurements. The
scaling parameters of the LPDM-B model are the measurement height zm, roughness
length z0, stability parameter zm-L, mixing layer height zi, and friction velocity
u*.
For this study data from the pre-alpine Rietholzbach catchment in the north-eastern part
of Switzerland are analysed. The tower is equipped with three ultrasonic anemometer
(CSAT3, Campbell Scientific, Logan, USA) at 2, 5.5, and 9Â m. At the top and bottom level
an open-path CO2/H2O infrared gas analyser (Li7500, Li-Cor, Lincoln, USA) is
installed as well. The tower is located in a grassland close to the valley bottom.
Similar to many other eddy covariance measurement locations the terrain is not flat
and the land use is not absolutely homogeneous (some individual trees). At the
Rietholzbach site wind direction is along the valley axis from western or eastern
directions and along this axis the topography is about constant with a slight slope of |
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