The area concerned which is adjacent to the city of Okaya is situated at the outlet of lake Suwa comprises the beginning part of the Valley of Tenryu and its eighboaring mountains. According to K. MISARA's article which was published more than 20 years ago and which reveals that the bending direction of a rice plant indicates the prevailing wind in autumn at the locality, the writer measured the bending direction of this crop this autumn and drew them in the map of 1:10000 which is shown in Fig. 2. It is indeed natural that at the Valley bottom prevail SW winds since Valley Tenryu runs in NE-SW direction, but it is eurious enough to find that there exist conspicuous western winds not only at both valley walls but also at the several alluvial fans in front of them.
In order to investigate the cause of prevalence of these western winds there, the writer furthermore observed the bending direction of the plant as far as in the surrounding region of Fig. 2, and drew them in Fig. 1, the rectangle in which corresponds to the area of Fig. 2. In this map he learned that SW winds exclusively prevail not only in the Suwa Basin, on both foothills of the Shioziri Pass but in the Ina Valley as well, and has ascertained that no wind blows into this area except the SW winds from the Ina Valley, which are the cause of the seasonal winds at the Valley bottom of Fig. 2.
According to the mechanical observations at the Kirigamine Weather Station situated at the summit of Vol. Kuruma-yama, the height of which is 1952m above sea level, however, the direction of the seasonal wind at the locality is S and SSW all through the year*. It is, therefore, not difficult to suppose the prevalence of southern winds in the air of the same height of Vol. Kurumayama also in the region of Fig. 1, even though SW winds prevail near the earth's surface by reason of the terrestrial modification, and it is also easy to infer the seasonal wind of the same direction over the area of Fig. 2, against which the upper part of the western ridge becomes a favourable screen. Since the wind velocity generally increases exceedingly in proportion to the height, it seems that the southern winds thus stroke against this precipitous valley wall blow downwards into the tributary valleys consequently eroding it to become the western winds in question, and these western winds further run upwards in the tributary valleys similarly growing in the opposite wall of Valley Tenryu, since this eastern valley wall is perfectly screened by the interfluve mountain ridge from the southern seasonal winds in the air.
* (the long arrow drawn at the summit of this volcano indicates the direction of the seasonal winds there.)
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