Modelling Canopy Flows over Complex Terrain
Recent studies of flow over forested hills have been motivated by a number of important applications including understanding CO\(_2\) and other gaseous fluxes over forests in complex terrain, predicting wind damage to trees, and modelling wind energy potential at forested sites. Current modelling studies have focussed almost exclusively on highly idealized, and usually fully forested, hills. Here, we present model results for a site on the Isle of Arran, Scotland with complex terrain and heterogeneous forest canopy. The model uses an explicit representation of the canopy and a 1.5-order turbulence closure for flow within and above the canopy. The validity of the closure scheme is assessed using turbulence data from a field experiment before comparing predictions of the full model with field observations. For near-neutral stability, the results compare well with the observations, showing that such a relatively simple canopy model can accurately reproduce the flow patterns observed over complex terrain and realistic, variable forest cover, while at the same time remaining computationally feasible for real case studies. The model allows closer examination of the flow separation observed over complex forested terrain. Comparisons with model simulations using a roughness length parametrization show significant differences, particularly with respect to flow separation, highlighting the need to explicitly model the forest canopy if detailed predictions of near-surface flow around forests are required.
KeywordsComplex terrain First-order mixing-length closure Flow separation Forest canopy Numerical modelling
- Burns SP, Sun J, Lenschow DH, Oncley SP, Stephens BB, Yi C, Anderson DE, Hu J, Monson RK (2011) Atmospheric stability effects on wind fields and scalar mixing within and just above a subalpine forest in sloping terrain. Boundary-Layer Meteorol 138:231–262. doi:10.1007/s10546-010-9560-6 CrossRefGoogle Scholar
- EDINA (2011) Digimap Ordnance Survey service. http://digimap.edina.ac.uk/. Accessed 13 June 2016
- Oldroyd HJ, Pardyjak ER, Huwald H, Parlange MB (2015) Adapting tilt corrections and the governing flow equations for steep, fully three-dimensional, mountainous terrain. Boundary-Layer Meteorol. doi:10.1007/s10546-015-0066-0
- Pinard JDJP, Wilson JD (2001) First- and second-order closure models for wind in a plant canopy. J Appl Meteorol 40(10):1762–1768. doi:10.1175/1520-0450(2001)040<1762:FASOCM>2.0.CO;2