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| Titel |
Investigation of the spatial variability and possible origins of
wind-induced air pressure fluctuations responsible for pressure pumping |
| VerfasserIn |
Manuel Mohr, Thomas Laemmel, Martin Maier, Matthias Zeeman, Bernard Longdoz, Dirk Schindler |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151177
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| Publikation (Nr.) |
 EGU/EGU2017-15734.pdf |
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| Zusammenfassung |
| The exchange of greenhouse gases between the soil and the atmosphere is highly
relevant for the climate of the Earth. Recent research suggests that wind-induced air
pressure fluctuations can alter the soil gas transport and therefore soil gas efflux
significantly.
Using a newly developed method, we measured soil gas transport in situ in a well
aerated forest soil. Results from these measurements showed that the commonly
used soil gas diffusion coefficient is enhanced up to 30% during periods of strong
wind-induced air pressure fluctuations. The air pressure fluctuations above the forest floor
are only induced at high above-canopy wind speeds (> 5 m s−1) and lie in the
frequency range 0.01-0.1 Hz. Moreover, the amplitudes of air pressure fluctuations in
this frequency range show a clear quadratic dependence on mean above-canopy
wind speed. However, the origin of these wind-induced pressure fluctuations is still
unclear.
Airflow measurements and high-precision air pressure measurements were conducted at
three different vegetation-covered sites (conifer forest, deciduous forest, grassland) to
investigate the spatial variability of dominant air pressure fluctuations, their origin and
vegetation-dependent characteristics. At the conifer forest site, a vertical profile of air
pressure fluctuations was measured and an array consisting of five pressure sensors were
installed at the forest floor. At the grassland site, the air pressure measurements
were compared with wind observations made by ground-based LIDAR and spatial
temperature observations from a fibre-optic sensing network (ScaleX Campaign
2016).
Preliminary results show that at all sites the amplitudes of relevant air pressure
fluctuations increase with increasing wind speed. Data from the array measurements reveal
that there are no time lags between the air pressure signals of different heights, but a
time lag existed between the air pressure signals of the sensors distributed laterally
on the forest floor, suggesting a horizontal propagation of the air pressure waves. |
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