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Open AccessArticle

Analysis of Air Pressure Fluctuations and Topsoil Gas Concentrations within a Scots Pine Forest

1
Environmental Meteorology, Albert-Ludwigs-University of Freiburg, Werthmannstrasse 10, D-79085 Freiburg, Germany
2
Soil Ecology, Albert-Ludwigs-University of Freiburg, Bertoldstrasse 17, D-79085 Freiburg, Germany
*
Author to whom correspondence should be addressed.
Atmosphere 2016, 7(10), 125; https://doi.org/10.3390/atmos7100125
Received: 29 July 2016 / Accepted: 29 September 2016 / Published: 1 October 2016
High-precision differential air pressure measurements were conducted in the below-canopy space of a Scots pine forest and in the forest soil to investigate small air pressure fluctuations and their effect on soil gas flux. In addition to air pressure measurements, tracer gas concentration in the soil and airflow characteristics above and below the canopy were measured. Results suggest that air pressure fluctuations in the frequency range of 0.01 Hz–0.1 Hz are strongly dependent on above-canopy wind speed. While amplitudes of the observed air pressure fluctuations (<10 Pa) increase significantly with increasing above-canopy wind speed, the periods decrease significantly with increasing above-canopy wind speed. These air pressure fluctuations are associated with the pressure-pumping effect in the soil. A pressure-pumping coefficient was defined, which describes the strength of the pressure-pumping effect. During the measurement period, pressure-pumping coefficients up to 0.44 Pa·s−1 were found. The dependence of the pressure-pumping coefficient on mean above-canopy wind speed can be described well with a polynomial fit of second degree. The knowledge of this relation simplifies the quantification of the pressure-pumping effect in a Scots pine forest considerably, since only the mean above-canopy wind speed has to be measured. In addition, empirical modeling revealed that the pressure-pumping coefficient explains the largest fraction of the variance of tracer gas concentration in the topsoil. View Full-Text
Keywords: turbulence; air pressure fluctuations; pressure pumping; gas transport; Scots pine (Pinus sylvestris L.) turbulence; air pressure fluctuations; pressure pumping; gas transport; Scots pine (Pinus sylvestris L.)
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Mohr, M.; Laemmel, T.; Maier, M.; Schindler, D. Analysis of Air Pressure Fluctuations and Topsoil Gas Concentrations within a Scots Pine Forest. Atmosphere 2016, 7, 125.

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