A shelterbelt study - relative shelter, effective winds and maximum efficiency.

Reports daily run-of-wind measurements, made for 3 years at distances of 3.5 h and 7 h to leeward of a 7-row shelterbelt about 6m.high. After elimination of variations in wind direction, the monthly values of relative shelter at these positions showed no evidence of an increase with time. The variations in wind direction were eliminated by regressions of monthly values of relative shelter on the monthly percentage frequency of effective winds, i.e. winds from the normal windward side of the shelterbelt. Using these regressions the maximum efficiency of the belt at 3.5 h was found to be 61%, and at 7 h it was 40%. Itis suggested that such values may be used as objective indices of the degree of shelter provided at a fixed point.