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Implementation of forest canopy in the MIUU mesoscale model. Mattias Mohr, Johan Arnqvist, Hans Bergström Uppsala University (Sweden). Project G oals. Project: Wind power over forests ( Vindforsk III) Better estimation of energy yield (wind resource) - PowerPoint PPT Presentation
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Mattias Mohr, Johan Arnqvist, Hans BergströmUppsala University (Sweden)
Implementation of forest canopy in the MIUU mesoscale model
Project 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
Ryningsnäs test site
140m high mast
18m high mast
T1, T2 = wind turbines
Measurement setupU, T, , Global radiation
U, T
U, T, , q
U, T,
U, T, q
U, T, , Net radiation
TU ,
Sonic ane-mometers, LiCor
MIUU mesoscale model
• Used for wind mapping of Sweden (Uppsala University, Weathertech)
• Higher order closure, prognostic TKE, no terrain smoothing, 1km resolution (mapping), 100m resolution (forest modelling)
• Very high resolution in boundary layer (canopy modelling: 1, 3, 6, 10, 16, 24, 35, 52, … m)
Wind profile over forests
• Bulk versuscanopy modelling
• Does it make any difference at allin mesoscalemodels?
Bulk versus canopy modelling
• Resource assessment benefit? Not sure
• Micro-scale siting benefit? Definitely
• In MIUU model wind-mapping setup: 5 vertical levels within forest anyway, so why not include canopy?
How to include this in the model?
• Production/dissipation term in TKE equation
LAD | horizontal | 3 - | horizontal | q2
where q2 = turbulent kinetic energy (TKE)
βp = 1.0 (canopy production coefficient)βd = 4.0 (canopy dissipation coefficient)
Seems to make little difference above forest. (Main part of TKE produced by strong wind shear above forest.)
Drag term for horizontal wind components (u, v)
LAD | horizontal | (same for v-component)
, = wind component
Halldin, S. (1985): Leaf and bark area distribution in a pine forest. In The forest atmosphere interaction, edited by B. A. Hutchison and B. B. Hicks (Dordrecht: Reidel Publishing Company), p. 39–58.
Lalic, B. and D. T. Mihailovic (2004): An Empirical Relation Describing Leaf-Area Density inside the Forest for Environmental Modeling. Journal of Applied Meteorology, Notes and Correspondence, Vol. 43, p. 641-645.
”Elevated” Monin Obukhov (MO) theory in model
• Replace elevation above ground with elevation above zero displacement
• Replace MO-similarity theory terms in forest with something else (what?)
• Lower boundary conditions have to be modified (energy balance, u*, … )
Master length scale• Length scale within forest
• Simple model of Inoue (1963):
l = 0.47 · (h – d) ≈ 2m
• Within canopy: Length scale constant with height
Seems to have very little influence on results.
Energy balance
• Has to be solved at each model level within canopy
• Direct shortwave radiation follows Beer’s law S↓ = S↓0 · exp(-0.5 · )
• Longwave radiation (Zhao and Qualls, 2006)
Start with idealised 1D simulations
• Run several days (diurnal cycle)
• Parameters used: 10m/s geostr. wind, average temperature profile, z0 = 1 m, h = 20 m, LAI = 5, pine forest, spring
• Compare results with bulk version
Idealised 1D results – diurnal variation
0 0 0
1 122
3 3
4
4
4
4
4
5
5
555
5
5
5
5
55
5
6
6
6
6
66
6
6
6
6
6
6
6
7
7
7
7
77
7
7
7
7
7
7
7
7
7
7
7
8
8
8
8
8
8
9
9
9
Model-prediced wind speed (fair-weather test case)
Local standard time
Hei
ght a
bove
gro
und
(m)
12 0 12 0 12 0 12 00
20
40
60
80
100
120
140
160
180
0
1
2
3
4
5
6
7
8
9
10
11
m/s
No wind in forest
Idealised 1D results – mean profiles
0 1 2 3 4 5 6 7 80
20
40
60
80
100
120
140
160
180
200
Mean Wind Speed (m/s)
Heig
ht a
bove
gro
und
(m)
Comparison of Bulk and Canopy Wind Profiles (4 day 1D test run)
Bulk forest (z0 = 1 m)
Forest canopy (additional drag terms)Logarithmic wind profile
4 day 1D simulation – Input data
• Temperature profiles from radio soundings atRyningsnäs
• Global radiation from measurements
• Geostrophic winds from Reanalysis
• Forest: hc, LAI, LAD(z), zm best guess
4 day 1D simulation - Ryningsnäs
0 2 4 6 8 10 12
20
40
60
80
100
120
140
Comparison of Bulk and Canopy Wind Profiles (05/04 - 08/04/2011)
Mean Wind Speed (m/s)
Hei
ght a
bove
gro
und
(m)
Forest canopy (additional drag terms)MeasurementsBulk forest (z0 = 1 m)
4 day 1D simulation - shear
• Comparison of shear exponents (4 days):
Shear exponentMeasurements 0.374
Forest canopy model 0.365
Bulk model 0.39
For comparison (annual values)42 Swedish forest site: 0.25 - 0.40 (median value 0.33)
(Source: ”Wind power in forests”, final report, Elforsk, published March 2013)
Summary & Conclusions
• Preliminary 1D results promising
• Still lot of work to do (lower boundary conditions, canopy energy balance, length scale…)
• Vertical resolution of 1D runs too time-consuming for 3D runs?
• Is vertical resolution of 3D runs enough for canopy model?
Future plans
• Refine forest canopy module in MIUU model
• Implement and run in 3D
• Study effects on resource assessment
• Implement forest canopy in WRF