Frequency of Occurrence of Fast Gusts of Wind Inside a Corn Canopy

Abstract

The removal from leaves of small particles such as pollen, dust or spores often requires gusts of wind having speeds that greatly exceed the mean wind speed. To determine the frequency of occurrence of such fast gusts we analyzed wind data that were measured inside a corn canopy using a fast-response (50 Hz) anemometer to obtain the probability density distribution of the total wind speed Q = (u2 + v2 + w2)½ and of the temporal change in wind speed ?Q for several sampling intervals. Gusts of wind with speeds exceeding the local mean wind speed by a factor of 3 or more were more frequent near the middle than near the top of the canopy and, for winds averaging 0.92 m s?1 for 1 h at mid-canopy, speeds as great as 4.4 times the mean occurred for about 0.8 s during the hour. We estimate that this relatively high speed occurred on at least 10 separate occasions during the hour-long observation period.