降雪粒子の大きさと落下速度の新観測法

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  • A new method of measuring snowflake size and falling velocity
  • コウセツ リュウシ ノ オオキサ ト ラッカ ソクド ノ シン カンソクホウ

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Customarily, the falling velocity of a particular snowflake is measured directly from the time interval taken for it to fall through a given vertical distance, and the size of the snowflakes is examined on dyed filter paper separately. That is, the direct and simultaneous measurements of the size and falling velocity of aggregate snowflakes in the falling space cannot be performed outdoors.<BR>In order to measure both at once, the following new technique has been developed. The moving snowflakes are photographed by two cameras (one camera measures the falling velocity, the other the size) against a dark background. The shutter speeds of the two cameras are set at 1/30 and 1/1000 second. Since both of them are operated simultaneously, two pictures for the same snowflakes are obtained. From the short streak in the picture with a slow shutter speed, the velocity is measured. From the camera with a faster shutter speed, the size and number of the snowflakes are obtained. These negative films are magnified by a factor of 1.5 by a slide projector. Thus, the size, falling velocity and mean concentration of falling snowflakes are measured simultaneously from each negative. This paper describes the effectiveness of this new method as demonstrated by outdoor experiments, and shows that the falling velocity depends upon the size and the concentration of snowflakes under calm conditions.

収録刊行物

  • 雪氷

    雪氷 43 (1), 1-8, 1981

    公益社団法人 日本雪氷学会

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