Studies of the phenomena of Waving plants (“HONAMI”) caused by wind

Abstract

A number of wind velocity profiles over a rice field obtained during the summer season under a nearly adiabatic condition are represented by the logarithmic law, i.e., U(z)=2.303/κV*logz-d/z0, z>d+z0;where κ, V*, d and z0 have their usual meanings respecitvely. The zero-plane displacement d is shown to have a maximum value at a certain critical wind velocity; and z0 and, consequently, the surface drag coefficient Cs are shown to attain minimun simultaneously at the same critical.These behaviors are related to predominance of the waving rice phenomena, whose period and amplitude being explained respectively by length and energy of the coupling turbulon in surface wind. The period of waving plants is computed as a passage time of coupling turbulon depending upon d and wind velocity, and is found at the critical velocity (ca. 5.5m/sec at 2m height) to coincide with the natural period of vibrating rice (ca. 1 sec). This coincidence is maintained even in the range of wind velocity over the critical value and to which the predominance of waving plants phenomena is attributed. Preliminary observations made by Suzuki (1948) are shown in accord well with the present considerations.