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| Titel |
On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study |
| VerfasserIn |
D. J. Durden, C. J. Nappo, M. Y. Leclerc, H. F. Duarte, G. Zhang, M. J. Parker, R. J. Kurzeja |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 12 ; Nr. 10, no. 12 (2013-12-23), S.8433-8443 |
| Datensatznummer |
250085490
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| Publikation (Nr.) |
 copernicus.org/bg-10-8433-2013.pdf |
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| Zusammenfassung |
| The interpretation of flux measurements in nocturnal conditions is typically
fraught with challenges. This paper reports on how the presence of wave-like
disturbances in a time series, can lead to an overestimation of turbulence
statistics, errors when calculating the stability parameter, erroneous
estimation of the friction velocity u* used to screen flux data,
and errors in turbulent flux calculations. Using time series of the pressure
signal from a microbarograph, wave-like disturbances at an AmeriFlux site
are identified. The wave-like disturbances are removed during the
calculation of turbulence statistics and turbulent fluxes. Our findings
suggest that filtering eddy-covariance data in the presence of wave-like
events prevents both an~overestimation of turbulence statistics and errors
in turbulent flux calculations. Results show that large-amplitude wave-like
events, events surpassing three standard deviations, occurred on 18% of
the nights considered in the present study. Remarkably, on flux towers
located in a very stably stratified boundary-layer regime, the presence of a
gravity wave can enhance turbulence statistics more than 50%. In
addition, the presence of the disturbance modulates the calculated turbulent
fluxes of CO2 resulting in erroneous turbulent flux calculations of the
order of 10% depending on averaging time and pressure perturbation
threshold criteria. Furthermore, the friction velocity u* was
affected by the presence of the wave, and in at least one case, a 10%
increase caused u* to exceed the arbitrary 0.25 m s−1
threshold used in many studies. This results in an unintended bias in the
data selected for analysis in the flux calculations. The impact of different
averaging periods was also examined and found to be variable specific. These
early case study results provide an insight into errors introduced when
calculating "purely" turbulent fluxes. These results could contribute to
improving modeling efforts by providing more accurate inputs of both
turbulent kinetic energy, and isolating the turbulent component of u*
for flux selection in the stable nocturnal boundary layer. |
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