WINDS ON THE RIDGE, VALLEY SLOPE AND VALLEY BOTTON. (1)

Abstract

In the previous paper the present author studied the relation between the wind direction and the topography at a station in a mountainous region, using an expression of the numerical index which was calculated from the topographical map (1:50, 000). At that time he pointed outt hat more detailed relationships must be investigated by the field observations. The reason for this is that the table work using the topographical map could not calculate the numerical index of microtopography both with the limits of the accurate calculation and of the. expression of contour lines at maps. The other results, obtained by the comparative studies of the diurnal change of air temperature, confirmed that the atmospheric turbulence plays the important role in a area within a small valley. Considering the results above-mentioned, he tried the observation of the atmospheric turbulence in a moderate. scale in a small area, Nishiura, Izu Peninsula. In order to obtain satisfactory results, firstly the preliminary observation is projected to select the observation. points at the various localities. The observation points, as shown in Fig. 1 and Tab. 1, were selected on the ridge, the upper and lower part of valley slope, and the valley bottom (stationtion No. -1, -2, -3, -4) of the lower, middle and upper course of the river (station No. 1-, 2-, 3-). Using the Mori-type anemograph, wind velocity. of maximum frequency along 16-directions were observed from 12h to 16h on March 8th, 1952. As shown in Fig. 2 (a), the difference of wind conditions at various points are comparatively great. After the analysis of variance (Tab. 2), summary of the preliminary observation is lead as follows: (1) On, the ridge (station 11, 21, 31) the prevailing wind direction, was from south to east with velocity of 3-5m/s. (2) As compared with this, at the valley slope the prevailing wind direction turns clockwise. At the valley bottom, the wind keeps still its clock wise. direction. (3) Above-mentioned results were average as shown in Fig. 2 (b). This is significant as the wind characteristics affected by the microtopography. (4) As a conclu.sion, it can be said that the simultaneously observed points in main observation must be selected at the area of one topographical unit, such as the ridge area, the valley bottom area, or the area of middle course of the river. Then, the author attemptedd to try the main observation using the Nakaasatype anemometer. The difference in type of the used instruments between preliminary and main observation is not significant from the results of comparative obsevation as shown in Tab. 3. In the main observation, carried out on March 21st and 22nd, he investigated the intensity of turbulence, mean wind, velocity, mean wind direction and its variance, from the value observed in every one minute at the four stations. The observation points reported in this paper were selected at the coastal station and the ridge stations of lower, middle and upper course of the river. Comparing the values with each other, following summary is obtained: (1) The intensity of tubulence g=_??_/u at each point isshown in Tab. 4 (a). According to the analysis of variance, the differences of magnitude and the. different relations, due to the dissimilar direction of the prevailing wind, are. not significant. It is meaningful, however, that the value at a particular point indicates the significant difference between that at the other point or under the diverse wind conditions at the same point. (2) The relation between the mean wind velocity and microtopography is, also not so clear as shown in Tab. 4 (b) from the results of the present observation. In general, the peculiar value of mean wind velocity appears different localities owing to the prevailing wind direction.