Mattias Mohr, Johan Arnqvist, Hans Bergström Uppsala University (Sweden) Simulating wind and turbulence profiles in and above a forest canopy using the MIUU mesoscale model

Project and Goals Project: Wind power over forests (Vindforsk III) Better estimation of energy yield (wind resource) Better estimation of turbine loads (wind shear, turbulence, forest clearings) Models should be developed for these purposes

MIUU mesoscale model Used for wind resource mapping of Sweden (e.g. Higher order closure, prognostic TKE, no terrain smoothing, 1km resolution Very high resolution in PBL (for canopy modelling: 1, 3, 6, 10, 16, 24, 35, 52, … m)

Wind profile over forests (conceptual)

How to include this in model?

How to include this in the model?

”Elevated” Monin Obukhov theory in model Substitute all terms with elevation above ground through elevation above zero displacement Replace MO-similarity theory terms below zero displacement height with something else (what?) Lower boundary conditions have to be modified

Master length scale Master length scale within forest has to be modified We chose simple model of Inoue (1963): l = 0.47 · (h – d) ≈ 2m Length scale constant with height within canopy However, this has very little influence on results

Energy balance

Summary Basic equations Include drag term F=Cd |U|U Solve the energy balance for each forest level Determine the radiative heating Short wave balance Long wave balance Source/sink from phase changes of water Turbulence closure Include equations for TKE- produktion, dissipation Determine master length scale in forest

Start with idealised 1D simulations Compare new simulated profiles with profiles from bulk layer model version and measurements Use forest drag terms in horizontal momentum equations and canopy energy balance (not in TKE equation) Run 24 hours (diurnal cycle) and take mean value Parameters used: 10m/s geostr. wind, average temperature profile, z 0 = 1m, h = 20m, LAI = 5, pine forest, total cloudiness = 50%

Preliminary 1D results

Comparison with measurements

Comparison with turbulence measurements

Summary & Conclusions Preliminary 1D results promising Still a lot of work to do (lower boundary conditions, canopy energy balance, length scale…) Vertical resolution of 1D results might be too time- consuming to run in 3D Is vertical resolution of 3D runs (2, 6, 12, 21, 33, 49, 72, 103, …m) enough for canopy model?