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Titel |
Determination of the correction function for the roughness sublayer for application of the aerodynamic method at a tall vegetation site |
VerfasserIn |
Friederike Rütz, Anywhere Tsokankunku, Franz X. Meixner, Thomas Foken |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250035516
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Zusammenfassung |
The diel variability as well as the magnitude and direction of the aerodynamic gradient
fluxes of reactive (NO-NO2-O3) and nonreactive (CO2 and H2O) trace gases were
investigated on a 32 m flux measurement tower above a spruce forest canopy at the
"Weidenbrunnen" research site (Fichtelgebirge, Germany). The measurements were
done within the framework of the EGER project. Eddy covariance measurements
were made at the top of the 32 m tower while the gradients for the aerodynamic
flux calculations were derived from the mixing ratios of the trace gases at the 31.5
m and 25 m levels of a trace gas profile measurement system on the tower. The
measurements were within the roughness sublayer, where the measured gradients are often
underestimated and an enhancement factor has to be applied to correct for the error
associated with measuring in the roughness sublayer. Therefore the profile and eddy
covariance measurement data, measured at several heights within the roughness sublayer,
were used to calculate φ* values for each half hour. The resulting φ* values were
merged with φ* values calculated from profile and eddy covariance measurements
above a cornfield (COPS experiment). Furthermore, an equation was fitted and
found to work best for φ* = -z
z*η , which was found to depend on the associated u*
values and is valid for u* > 0.2 m/s with η = 0.6. In this process, each half hour
gradient flux calculated from the aerodynamic gradient method was corrected for the
roughness sublayer effect by applying the respective φ* factor for that half hour period. |
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