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Titel |
Local wind phenomena at the Waldstein/Weidenbrunnen FLUXNET site |
VerfasserIn |
S. Schier, F. X. Meixner, T. Foken |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250021342
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Zusammenfassung |
Two Intensive Observation Periods (IOP) of the EGER project (ExchanGE processes in
mountainous Regions) were performed at the Waldstein/Weidenbrunnen FLUXNET site
(DE-Bay) in the Fichtelgebirge/Germany. IOP1 was conducted in September and October
2007, IOP2 in June and July 2008. The project is focused on the detailed quantification of
relevant processes within the soil-vegetation-atmosphere system by observing diurnal and
annual cycles of energy, water and trace gases. The atmospheric boundary layer was
profiled with an acoustic and radar remote sensing system (SODAR-RASS). The
SODAR provided 10 minute mean profiles up to 500Â m a.g.l. In contrast to IOP1
a second SODAR (referred to as miniSODAR) without a RASS-extension was
used during IOP2 and provided 5 minute mean profiles up to 200Â m a.g.l. The
aims of this study included the observation of local wind phenomena at the site, the
determination of their frequency and their relation to surrounding meteorological
circumstances.
During both IOPs some nocturnal low-level jets (LLJ) with a duration time of several
hours were observed. Maximum horizontal wind speed (vhmax) was in the range from 11.5 to
12.3 m s-1 for IOP1 and in the range from 8.0 to 11.6 m s-1 for IOP2. The height of
vhmax varied between 100 and 230Â m a.g.l. Most of the LLJ events were characterised by
an approaching flow from south-easterly directions. Another phenomenon was
observed in the profile of the wind vector. It showed a strong turn of the wind direction
with increasing height. At night times and during the morning hours flows above
the canopy came from the east while the geostrophic wind approached from the
south-westerly directions. The topography and resulting canalising effects seem to be
the reason for the generation of LLJ as well as for the turn of the wind direction. |
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