Winds in a V-shaped Small Valley

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Abstract
An observation was carried out during July 27-31, 1957, in a small V-shaped valley dissecting Sugadaira high land, Nagano Prefecture. [I] When the prevailing upper winds crossed over the valley, the following results were obtained. (1) Ratio of the wind speed at the valley stations to that at the station situated on the horizontal high land surface is smaller at night than in the daytime. It is the smallest generally in the valley bottom and becomes larger to the upper edge of the valley side slope. (2) Deviation of the wind direction from the prevailing winds reached almost 90° at the lower part of the valley slope and had diverse component in the valley bottom. From these circumstances the eddies formed in the valley seemed to have some twisted character in the valley bottom. (3) The ratio of the wind speed at the valley stations dependen upon the prevailing wind speed, but an inverse relation in the daytime and a positive relation at night was found. This is originated by the development of relatively strong valley winds and the weak mountain winds in this region. (4) The eddies in the valley were produced even under the low speed (1-2m/s at 1 meter height) of the prevailing wind and irrespectively of time of day or night. [II] When the prevailing wind direction coincides with the running direction of the valley, there appear almost same wind speedsin the valley bottom as that on the open horizontal land. In some cases, however, the former was stronger than the later. Especially, the station located in the valley bottom becomming narrow had an anomalously wide fluctuation of the wind direction and a relatively strong wind speed.

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