Examination of the mechanism behind observed canopy waves
•A new linear analysis shows that shear instability is the cause of canopy waves.•Conditions for Holmboe instabilities is shown to exist over forests.•Waves resembling both shear and Holmboe instabilities were found in measurements.•The existance of wave oscillations could be an important factor on...
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| Published in: | Agricultural and forest meteorology Vol. 218-219; pp. 196 - 203 |
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| Main Authors: | , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Elsevier B.V
15-03-2016
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | •A new linear analysis shows that shear instability is the cause of canopy waves.•Conditions for Holmboe instabilities is shown to exist over forests.•Waves resembling both shear and Holmboe instabilities were found in measurements.•The existance of wave oscillations could be an important factor on wind-turbine loads.
In this paper, we document the existence of wave-like motions above a forest canopy using data taken from a 138m high tower placed within a forest. Characteristics of the waves are examined in relation to their possible effects on wind energy. It is shown that when the wave signal is relatively clean, the phase lag between horizontal and vertical velocity is close to 90°, which limits the contribution of the waves to the downward momentum flux. Numerical solutions of the linear wave equations agree with measurements in terms of wave period and the vertical shape of the wave amplitude. Linear analysis show that shear instability is the cause of unstable wave growth, and that the fastest growing unstable wave number typically has a period of 10–100s. In addition to the shear instability, the linear analysis predicts that under certain conditions instabilities of the Holmboe kind can develop over forests. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0168-1923 1873-2240 1873-2240 |
| DOI: | 10.1016/j.agrformet.2015.11.024 |