Measured winds about a thick hedge

We measured mean windspeed and turbulent kinetic energy (15 min averaging intervals) in the region of a tall cypress hedge (height H = 8 m; thickness X = 3 m), the observed patterns resembling those previously reported for dense, natural shelterbelts, except in circumstances where secondary shelterbelts at the site played a role. Along a transect at height z = H/4, minimum mean windspeed always occurred at the anemometer closest to the hedge (H/4 from the downwind edge), and mean windspeed at that point was only about 20–25% of the upwind value, with weak sensitivity to thermal stratification and to the orientation of the approaching wind. We also examined time series of velocity from sonic anemometers placed against the upstream and downstream faces of the hedge, forming statistics over averaging intervals selected by the criterion that lowpass filtered wind direction should never reverse to exchange the ‘upwind’ and ‘downwind’ sides. Whatever the far upwind angle of approach and corresponding angle of incidence on the upwind face, the mean wind emerged from the downwind face aligned with the normal.