抄録
In 14 Sept. 1954, when the typhoon No. 12 was at Japan sea, we observed the wind over the rice field at Chigasaki, making use of 6 small Robinson cup anemometers installed to the pole of 6m high. The vertical distributions of wind velocity and turbulence were obtained.
The following results were obtained:
(1) The vertical distributions of mean wind velocity were well represented by the logarithmic law,
U(z)=2.30V*/klogz-d/z0,
and the roughness parameter z0 and zeroplane displacement d were found to change in accord with the wind velocity. When the wind velocity at 2m height was within the range 5.5-7.7m/sec, d was reduced and z0 was increased respectively with the wind velocity.
(2) Observations obtained before at other rice fields were also reconsidered, and it was found that, except cases the wind velocity was less than 1m/sec, d was incresed and z0 was decreased respectively with the wind velocity up to 5m/sec, and that, however, when the wind velocity was increased over 5m/sec, d was reduced and z0 was increased respectively. (Fig. 2)
(3) We observed the fluctuation in windy elocity by means of reading anemometer's counter at every 5 seconds. The energy of turbulence ‹u′2› was increased very little with the averaging time ranging from 1 to 30 minutes, and was increased with height. The intensity of turbulence ‹u′2›1/2/U was decreased slightly with height.
(4) Eulerian-correlation coefficients for velocity fluctuation were calculated and the empirical result of R(t)=1-const.t1/3
was obtained.
These results obtained are apparently different from the theoretical ones based on the Similarity theory of Turbulence. These discrepancies might be partly due to the fact that the inertial subrange of turbulence is too small to be observed by the method mentioned above.
