gustiness parameterization in the atmospheric boundary layer
DESCRIPTION
Gustiness parameterization in the atmospheric boundary layer. Irene Suomi Timo Vihma Sven-Erik Gryning. Definition. Peak gust ( or here gust ) is the maximum wind speed of short duration (t = 1…3 s) during a sampling period of length T=10min…1h. - PowerPoint PPT PresentationTRANSCRIPT
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Gustiness parameterization in the atmospheric boundary layer
Irene SuomiTimo VihmaSven-Erik Gryning
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Definition
Peak gust (or here gust) is the maximum wind speed of short duration (t = 1…3 s) during a sampling period of length T=10min…1h.
Gust factor is the ratio of peak gust and mean wind speed:
𝐺=𝑈𝑚𝑎𝑥
𝑈
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Motivation• large impacts: in Finland typically cut trees/forests, power
cuts, broken structures, etc• relevant for the wind energy (siting and turbine control) at
different heights (~100m)• gusts are not (yet) directly available from numerical
weather prediction models: parameterizations are needed
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Research questions• Are gust parameterizations applicable above 10 m
height? • What kind of a gust parameterization method is optimal
(based on observations)?
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Overview• Observations• Gust parameterization methods• A new method• Results• Conclusions and ongoing/future work
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Observations• Two weather masts:
Isosaari (83m) and Loviisa (143m)
• One year of data: 4/2009-3/2010, excluding from Isosaari months when sea ice
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Observations
Loviisa
Isosaari
30m
103m
143m
42m
62m
83m
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Type A Type B
• Wieringa (1973, W73)
G = f ( U, t, T, z, z0 )
• Woetman-Nielsen and Petersen (2001, WNP01)
G = f ( U, u*0, w* )
• Wichers Schreur and Geertsema (2008, WSG08)
G = f ( U, t, T, z, E )
U = mean wind speedt = gust durationT = sampling periodz = height a.g.l.u*0 = surface firction velocityw*0 = convective velocity scaleE = turbulent kinetic energy = potential temperature
• Brasseur (2001, B01)G = f ( U, z, , v, E )
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Gust parameterization methods
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A new method (”type A”)From the definition of gust factor:
where is the normalized gust.For unstable conditions:
and stable conditions:
(Gryning et al, 1987)
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𝐺=𝑈𝑚𝑎𝑥
𝑈 =1+𝑈𝑚𝑎𝑥−𝑈
𝜎𝑢
𝜎𝑢
𝑈
𝐺=1+𝑔𝑥𝜎𝑢
𝑈
𝑔𝑥=(𝑈 ¿¿𝑚𝑎𝑥−𝑈) /𝜎𝑢¿
𝜎 𝑢(𝑧 )=𝑢∗ [0.35(− 𝑧𝑘𝐿 )
2 /3
+(2− 𝑧h
)]1/2
𝜎 𝑢(𝑧 )=2𝑢∗(1−𝑧h
)1/2
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Results: Isosaari East/South (marine sector)
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OBS W73
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OBS WNP01
Results: Isosaari East/South (marine sector)
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OBS New method
Results: Isosaari East/South (marine sector)
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OBS W73
Results: Isosaari West (”rough” sector)
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OBS WNP01
Results: Isosaari West (”rough” sector)
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OBS New method
Results: Isosaari West (”rough” sector)
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OBS WNP01
Results: Loviisa North (land sector)
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OBS New method
Results: Loviisa North (land sector)
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Conclusions• In marine sector stability did not have significant role• Over rough surface, stability had effect, but the method by
WNP01 overestimated it, especially in Loviisa with unstable conditions
• The new method performed best in all cases. But: tuning of normalized gust is needed
• Ongoing / future work:• Normalized gust: gx = f ( t, T, z0, z, ? )• Test all methods within NWP model framework
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AcknowledgementsThe research leading to these results has received funding from the European Research Council under the European Community's 7 th Framework Programme (FP7/2007-2013) / ERC grant agreement number 227915, project PBL-PMES.