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Serafimovich, Andrei ; Thomas, Christoph ; Foken, Thomas:
Vertical and horizontal transport of energy and matter by coherent motions in a tall spruce canopy.
In: Boundary-Layer Meteorology.
Bd. 140
(2011)
Heft 3
.
- S. 429-451.
ISSN 1573-1472
DOI: https://doi.org/10.1007/s10546-011-9619-z
Abstract
In the frame of the EGER (ExchanGE processes in mountainous Regions) project the contribution of coherent structures to the vertical and horizontal transport in a tall spruce canopy was investigated. Combination of measurements done in vertical and horizontal directions allows us to investigate coherent structures, their temporal scales, their role in flux transport, vertical coupling between the subcanopy, canopy and air above the canopy, and horizontal coupling in the subcanopy layer. The temporal scales of coherent structures detected with the horizontally distributed systems in the subcanopy layer were larger than the temporal scales of coherent structures detected with the vertically distributed systems. The flux contribution of coherent structures to the momentum and sensible heat transport was found to be dominant in the canopy layer. Carbon dioxide and latent heat transport by coherent structures increases with height and reaches a maximum at the canopy height. The flux contribution of the ejection decreases with increasing height and becomes dominant above the canopy level. The flux fraction transported during the sweep increases with height and becomes the dominating exchange process at the upper canopy level. The determined exchange regimes indicate consistent decoupling between the sub-canopy, canopy and air above the canopy during evening, night and morning hours, whereas the coupled and coupled by sweeps states between layers were observed mostly during the day time. Furthermore, the horizontal transport of sensible heat by coherent structures was investigated and the heterogeneity of contribution of coherent events to the flux transport was shown. The scheme to determine the horizontal coupling by coherent structures in the subcanopy layer was proposed. It was shown that the subcanopy layer was horizontally coupled mainly in the wind direction. The vertical coupling in most cases was observed together with stream-wise horizontal coupling, whereas the cross-stream direction was decoupled.