Variation of Aerodynamical Characteristics of a Barley Field with Growth

The data of wind and temperature profiles in the low-level air layers over the barley field were used to study the magnitudes of the profile parameters (z0, d, V* and Cd) and their variations with wind velocity and the growth conditions of the crop plants. The profile measurements were made on a 1.5ha field of the barley during the period from November 1964 to June 1965. All wind profile parameter computations are based on the data of ten-minute mean wind velocity profiles. The results obtained are summarized as follows:1. The zero plane displacement (d) increases with the plant height but decreases inversely with the wind velocity. An exponential function of the plant height approximates the variation of d. The value of exponent decreases with wind velocity.2. The roughness parameter (z0) decreases slightly with the wind velocity in the early stages of plant growth, but it increases inversely with the wind velocity in the later stages of the growth. Under the conditions that h is larger than 5cm, z0 is found to be proportional to hl. The exponent varies also from 0.75 at weak wind velocity to 1.35 at at strong wind velocity.3. Surface drag coefficient (Cd) varies with the wind velocity and the plant height. The coefficient is proportional to a power of the plant height in the same manner as z0 (see Fig. 5). The variation of friction velocity (V*) with both the wind velocity and the plant growth is expressed approximately byV*=0.4/0.74+Fu1501.02+0.29F.