Boundary-Layer Meteorology

, Volume 164, Issue 1, pp 1–17 | Cite as

Enhanced Scalar Concentrations and Fluxes in the Lee of Forest Patches: A Large-Eddy Simulation Study

Research Article
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Abstract

By means of large-eddy simulation, we investigate the transport of a passive scalar in the lee of forest patches under neutral atmospheric conditions in flat terrain. We found a pronounced local enhancement of scalar concentration and scalar flux in the lee zone of the forest, while further downstream above the unforested surface, the scalar transport adjusted to an equilibrium with the underlying surface conditions. By means of a term-by-term analysis of the scalar transport equation, we determined the local accumulation of the scalar to be caused by the convergence of: (1) mean and turbulent streamwise transport, (2) mean vertical transport. However, the relative importance of each transport mechanism for the accumulation process was found to depend strongly on forest density. Based on systematic parameter changes, we found concentrations to significantly increase with increasing forest density and with decreasing wind speed, while fluxes were invariant to wind speed and showed a similar relation to forest density as for the concentrations. Despite the scalar sources—ground and/or canopy sources—a local flux enhancement was present in the lee zone. Finally, we provide a first step towards localizing enhanced concentrations and fluxes at micrometeorological sites.

Keywords

Enhanced scalar fluxes Forest-edge flow Large-eddy simulation Lee recirculation Scalar accumulation 

References

  1. Armaly BF, Dursts F, Pereira JCF, Schönung B (1983) Experimental and theoretical investigation of backward-facing step flow. J Fluid Mech 127:473–496CrossRefGoogle Scholar
  2. Belcher SE, Jerram N, Hunt JCR (2003) Adjustment of a turbulent boundary layer to a canopy of roughness elements. J Fluid Mech 488:369–398CrossRefGoogle Scholar
  3. Belcher SE, Harman IN, Finnigan JJ (2012) The wind in the willows: flows in forest canopies in complex terrain. Annu Rev Fluid Mech 44:479–504CrossRefGoogle Scholar
  4. Bergen JD (1975) Air movement in a forest clearing as indicated by smoke drift. Agric Meteorol 15:165–179CrossRefGoogle Scholar
  5. Cai XM, Barlow JF, Belcher SE (2008) Dispersion and transfer of passive scalars in and above street canyons—large-eddy simulations. Atmos Environ 42:5885–5895CrossRefGoogle Scholar
  6. Cassiani M, Katul GG, Albertson JD (2008) The effects of canopy leaf area index on airflow across forest edges: large-eddy simulation and analytical results. Boundary-Layer Meteorol 126:433–460CrossRefGoogle Scholar
  7. Chan TL, Dong G, Leung CW, Cheung CS, Hung WT (2002) Validation of a two-dimensional pollutant dispersion model in an isolated street canyon. Atmos Environ 36:861–872CrossRefGoogle Scholar
  8. Detto M, Katull GG, Siqueira M, Juang JY, Stoy P (2008) The structure of turbulence near a tall forest edge: the backward-facing step flow analogy revisited. Ecol Appl 18:1420–1435CrossRefGoogle Scholar
  9. Dupont S, Brunet Y (2008) Edge flow and canopy structure: a large-eddy simulation study. Boundary-Layer Meteorol 126:51–71CrossRefGoogle Scholar
  10. Dupont S, Bonnefond JM, Irvine MR, Lamaud E, Brunet Y (2011) Long-distance edge effects in a pine forest with a deep and sparse trunk space: in situ and numerical experiments. Agric For Meteorol 151:328–344CrossRefGoogle Scholar
  11. Finnigan JJ (2000) Turbulence in plant canopies. Annu Rev Fluid Mech 32:519–571CrossRefGoogle Scholar
  12. Finnigan JJ, Belcher SE (2004) Flow over a hill covered with a plant canopy. Q J R Meteorol Soc 130:1–29CrossRefGoogle Scholar
  13. Flesch TK, Wilson JD (1999) Wind and remnant tree sway in forest cutblocks. I. Measured winds in experimental cutblocks. Agric For Meteorol 93:229–242CrossRefGoogle Scholar
  14. Foken T (2008) Micrometeorology. Springer, Berlin 306 ppGoogle Scholar
  15. Fontan S, Katul GG, Poggi D, Manes C, Ridol L (2013) Flume experiments on turbulent flows across gaps of permeable and impermeable boundaries. Boundary-Layer Meteorol 147:21–39CrossRefGoogle Scholar
  16. Frank C, Ruck B (2008) Numerical study of the airflow over forest clearings. Forestry 81:259–277CrossRefGoogle Scholar
  17. Kanani-Sühring F, Raasch S (2015) Spatial variability of scalar concentrations and fluxes downstream of a clearing-to-forest transition: an LES study. Boundary-Layer Meteorol 155:1–27CrossRefGoogle Scholar
  18. Katul GG, Finnigan JJ, Poggi D, Leuning R, Belcher SE (2006) The influence of hilly terrain on canopy-atmosphere carbon dioxide exchange. Boundary-Layer Meteorol 118:189–216CrossRefGoogle Scholar
  19. Klaassen W, Van Breugel PB, Moors EJ, Nieveen JP (2002) Increased heat fluxes near a forest edge. Theor Appl Climatol 72:231–243CrossRefGoogle Scholar
  20. Kostas J, Soria J, Chong MS (2002) Particle image velocimetry measurements of a backward-facing step flow. Exp Fluids 33:838–853CrossRefGoogle Scholar
  21. Letzel MO, Krane M, Raasch S (2008) High resolution urban large-eddy simulation studies from street canyon to neighbourhood scale. Atmos Environ 42:8770–8784CrossRefGoogle Scholar
  22. Letzel MO, Helmke C, Ng E, An X, Lai A, Raasch S (2012) LES case study on pedestrian level ventilation in two neighbourhoods in Hong Kong. Meteorol Z 21:575–589CrossRefGoogle Scholar
  23. Markfort CD, Porté-Agel F, Stefan HG (2014) Canopy-wake dynamics and wind sheltering effects on Earth surface fluxes. Environ Fluid Mech 14:663–697CrossRefGoogle Scholar
  24. Maronga B, Gryschka M, Heinze R, Hoffmann F, Kanani-Sühring F, Keck M, Ketelsen K, Letzel MO, Sühring M, Raasch S (2015) The parallelized large-eddy simulation model (PALM) version 4.0 for atmospheric and oceanic flows: model formulation, recent developments, and future perspectives. Geosci Model Dev 8:2515–2551CrossRefGoogle Scholar
  25. Miller DR, Lin JD, Lu ZN (1991) Air flow across an alpine forest clearing: a model and field measurements. Agric For Meteorol 56:209–225CrossRefGoogle Scholar
  26. Poggi D, Katul GG (2007) Turbulent flows on forested hilly region terrain: the recirculation. Q J R Meteorol Soc 133:1027–1039CrossRefGoogle Scholar
  27. Queck R, Bernhofer C, Bienert A, Eipper T, Goldberg V, Harmansa S, Hildebrand V, Maas HG, Schlegel F, Stiller J (2015) TurbEFA: an interdisciplinary effort to investigate the turbulent flow across a forest clearing. Meteorol Z 23:637–659CrossRefGoogle Scholar
  28. Raasch S, Schröter M (2001) PALM—a large-eddy simulation model performing on massively parallel computers. Meteorol Z 10:363–372CrossRefGoogle Scholar
  29. Raupach MR, Weng WS, Carruthers DJ, Hunt JCR (1992) Temperature and humidity fields and fluxes over low hills. Q J R Meteorol Soc 118:191–225CrossRefGoogle Scholar
  30. Ross AN (2008) Large-eddy simulations of flow over forested ridges. Boundary-Layer Meteorol 128:59–76CrossRefGoogle Scholar
  31. Ross AN (2011) Scalar transport over forested hills. Boundary-Layer Meteorol 141:179–199CrossRefGoogle Scholar
  32. Ross AN, Baker TP (2013) Flow over partially forested ridges. Boundary-Layer Meteorol 146:375–392CrossRefGoogle Scholar
  33. Ross AN, Harman IN (2015) The impact of source distribution on scalar transport over forested hills. Boundary-Layer Meteorol 156:211–230CrossRefGoogle Scholar
  34. Schlegel F, Stiller J, Bienert A, Hg Maas, Queck R, Bernhofer C (2014) Large-eddy simulation study of the effects on flow of a heterogeneous forest at sub-tree resolution. Boundary-Layer Meteorol 154:27–56CrossRefGoogle Scholar
  35. Sogachev A, Leclerc MY, Zhang G, Rannik Ü, Vesala T (2008) CO\(_{2}\) fluxes near a forest edge: a numerical study. Ecol Appl 18:1454–1469CrossRefGoogle Scholar
  36. Wilson JD, Flesch TK (1999) Wind and remnant tree sway in forest cutblocks. III. A windflow model to diagnose spatial variation. Agric For Meteorol 93:259–282CrossRefGoogle Scholar
  37. Yang B, Raupach MR, Shaw RH, Paw UKT, Morse AP (2006) Large-eddy simulation of turbulent flow across a forest edge. Part I: flow statistics. Boundary-Layer Meteorol 120:377–412CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  1. 1.Institut für Meteorologie und KlimatologieLeibniz Universität HannoverHannoverGermany

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