Measuring turbulent gust impressions in a forested canopy

Thursday, 18 December 2014
April Hiscox and Katherine Ertell, University of South Carolina, Columbia, SC, United States
The temporal and spatial characteristics of tree-sway motions and their aerodynamic interactions with coherent turbulence wind fields in a forest (Howland Forest, ME) are examined. Year round measurements of turbulence where taken at heights, above, below, and in the live crown. Additionally measurements of tree bole motion were taken simultaneously for 150 trees surrounding the main meteorological tower. To identify the gust impressions and further understand the timing, spacing and intensity of momentum flux, a a multi-resolution decomposition (MRD) technique was used to find the dominant eddy size. Fourier analysis was applied to each tree for the corresponding time and changes in dominant tree frequency were mapped over time. Results indicate that the most coherency in stand-scale motion occurs when frequency changes are mapped at the same time resolution of the dominant eddy size. Through a mapping-displacement comparison, the sub-mesoscale motions of a canopy atmosphere and their effect on the tree's movement as well as fluxes of energy will be better understood.