Canopy waves, observations and predictions from lineartheory
(English)Manuscript (preprint) (Other academic)
In this paper the existence of canopy waves is examined using measurements from a 138 m high tower placed in a forest. Characteristics of the waves are examined in relation to wind energy. Using wavelet analysis it is shown that when the wave signal is clear, the phase lag between horizontal and vertical velocity is close to 90 degrees, which limits the contribution of the waves to themomentum flux. Results from numerical solution of linear wave equations is shown to agree with measurements in terms of wave period and the vertical shape of the wave amplitude. Linear analysis and measurements suggests that Kelvin-Helmholtz instability causes unstable wave growth and that the most unstable wave number normally has a period of 10-100 s. In addition to the Kelvin-Helmholtz instability, the linear analysis predicts that instabilities of the Holmboe kind, with higher frequency, can develop over forests in certain conditions.
Forest, Holmboe instability, Kelvin-Helmholtz instability, Linear wave theory, Shear instability, Wind power
Meteorology and Atmospheric Sciences
IdentifiersURN: urn:nbn:se:uu:diva-237763OAI: oai:DiVA.org:uu-237763DiVA: diva2:768816