Strömningen i och över en skog : utvärdering av en 'mixing-layer' hypotes

• Main Author: Arnqvist, Johan
• Format: Others
• Language: Swedish
• Published: Uppsala universitet, Luft-, vatten och landskapslära 2009
• Subjects: Mixing-layer; Canopy; Wind profile; Kelvin-Helmholtz waves; Roughness sublayer; Nyckelord: Mixing-layer; Vindprofil; Skog; Kelvin-Helmoltz-vågor; Meteorology; Meteorologi
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-105408

A new theory for predicting the windprofile over a canopy has been evaluated. The theory was first presented by Harman and Finnigan (2007). The theory relies on the forming of a mixing-layer above the canopy, due to different mean wind in and above the canopy. Characteristics from both mixing-layer and Monin Obukhov similarity theory have been used to develop the governingequations that give the wind profile. The theory has been used to calculate wind profiles for sixdifferent atmospheric stabilities. In order to evaluate the theory, profiles from the theory have beencompared to measurements from Jädraås forest, Sweden. Profiles from Monin Obukhov similarity theory were also used for comparison.In general the mixing-layer theory gives better results than Monin Obukhov similarity theory. Agreement with measurements is good in neutral conditions, but fails when the atmospheric stability is altered, especially in convective conditions. This is believed to be due to the canopy lacking in thickness. The mean wind speed is systematically underestimated and this is also believed to be caused by insufficient thickness of the canopy. A correction for this behaviour is proposed. The theory gives higher values of the mean wind speed in convective conditions with the correction and the calculated values of mean wind speed are closer to the measurements.