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| Titel |
Linking CO2-advection estimates to vegetation structure at a forest site |
| VerfasserIn |
Lukas Siebicke, Andrei Serafimovich, 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 |
250039501
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| Zusammenfassung |
| Surface exchange flux measurements of Net Ecosystem Exchange NEE are incomplete if
only the turbulent flux is considered and advection neglected. However, including advective
terms in the budget has not proven to be a robust alternative since the uncertainties inherent
in advection estimates are large und thus increase the uncertainty and scatter of
NEE estimates. The current study investigates some of the processes generating
measured horizontal CO2 concentration gradients, which are generally used to compute
horizontal advective flux terms. In contrast to standard methodology where gradients are
computed over 30 minute time frames and a spatial extend in the order of tens to
hundreds of meters, the focus of this study is on short and small events such as
coherent structures. Moreover, we consider the effect of vegetation structure on
concentration gradients. Our results suggest that coherent structures might act as a transfer
function between vegetation structure such as Plant Area Index PAI and subcanopy
CO2 concentration. Very local mixing of a CO2 concentration distribution with
strong vertical gradients by coherent structures is an alternative explanation for
horizontal variability of subcanopy CO2 concentration as opposed to consistent larger
scale motion representative for the whole area under study, which is an often made
assumption. The small scale variability of vegetation structure leads to high local
variability of concentration gradients. Thus gradients are not representative for the scale
they need to be to complement above canopy turbulent flux measurement with
advective flux terms. Our findings do not directly improve the NEE budget but try to
shed some light on the mechanisms generating the observed CO2 concentration
signal. |
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