The influence of wind speed and direction on the reduction of wind speed leeward of a medium porous hedge

Daily run-of-wind (km) was recorded at a control station in the open and at a distance of $\text{4 H}$ (where $\text{H}$ is barrier height) leeward of a medium porous type of hedge during the spring and autumn periods between 1979 and 1981. Daily relative winds (RW) and the run-of-wind differences between the open and sheltered positions (DU) were derived from these measurements. RW at 4 $\text{H}$ was found to be primarily a function of the incident wind angle and independent of the mean open wind speed within the range 1–12 ms⁻¹. The RW at the fixed position was, therefore, suggested as a useful single index of the combined influence of wind direction and that of the barrier itself. For a particular RW value the daily run-of-wind difference between open and sheltered positions was found to vary positively with the mean daily wind speed.