| Popis: |
Wind and temperature profiles were measured above irrigated and non-irrigated field beans in 1972, and potatoes in 1973, and the zero-plane displacement d and roughness length z 0 were derived. For both crops the ratios of d and z 0 to crop height h varied little through the season; typical values of d / h were 0.66 for beans and 0.78 for potatoes, and of z 0 / h were 0.077 and 0.041 respectively. For both crops the seasonal variation of d / h that did occur was related to the foliage area density. There was good evidence for beans and a suggestion for potatoes that either z 0 / h or d / h decreased with increasing wind speed, but it was not possible to tell whether it was d or z 0 that changed. There was no evidence for either crop that d / h was affected by thermal stability for − 0.2 Ri Ri is the Richardson number. For beans the drag coefficient C M , with respect to a height of 2 h , was constant, with a mean value of 0.022 ± 0.002. For potatoes, the crop lodged: before lodging C M was 0.014 ± 0.001, and afterwards was twice this value. |
