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| Titel |
Influence of canopy foliage on turbulence above tall deciduous vegetation |
| VerfasserIn |
Metodija Shapkalijevski, Arnold Moene, Huug Ouwersloot, Edward Patton, Jordi Vilà-Guerau de Arellano |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109901
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| Publikation (Nr.) |
 EGU/EGU2015-9856.pdf |
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| Zusammenfassung |
| In this study, the role of tree phenology on the atmospheric turbulence over tall vegetation is
investigated. Our aim is to study dimensionless mean gradients, variances, and the
turbulent kinetic energy (TKE) within the roughness sublayer (RSL), and their
dependence on the leaf state of the canopy and the stability regimes. To do this, we
analyse observations, that are continuously collected over a whole season above and
in a walnut tree orchard during the Canopy Horizontal Array Turbulence Study
(CHATS) field experiment near Dixon, California. To support this data analysis, we
compare profiles of vertical fluxes and co-variances, as well as vertical gradients of
mean wind, temperature and humidity, with empirically derived dimensionless
gradients from previous studies and results from a second-order closure turbulence
diagnostic model. In doing so, we study the differences in the calculation of the
dimensionless gradients between recently developed model approaches that account for
the RSL effects on these gradients against representations that omit those effects.
The observations and model results are non-dimensionalized using atmospheric
surface layer scaling, paying special attention to the displacement height. The latter is
calculated from the observations and depends on the variable under consideration and
the leaf state. Our results for the dimensionless gradients of momentum, heat and
moisture show a reduction of these variables closer to the canopy top compared to the
standard Monin-Obukhov similarity theory (MOST) for both unstable and near
neutral conditions. We find that the reduction is larger for canopy with leaves than
for leafless canopy. This confirms the applicability of the aforementioned RSL
models. Their results are in better agreement with the observations for the fully
vegetated canopy then for the leafless canopy. With regard to the TKE-budget, our
analysis shows that turbulent transport is increasingly important term of the budget
when approaching heights closer to the canopy top. However, the results are very
sensitive to the choice of the displacement height. Our findings indicate the need (a) to
account for the effects of the roughness sublayer in calculating and interpreting
flux-gradient relationships and TKE above a deciduous forest, and (b) to include in these
calculations a displacement height that takes the canopy leaf state into account. |
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