Snow particle speeds in the blowing snow
Résumé
Snow particle speeds are one of the key issues in order to deepen our understanding for the internal structures of blowing snow. In this study, we utilized the snow particle counter (SPC) developed to observe the snow particle size distribution and the mass flux every one second. We have recorded the direct output signal from the transducer with high frequency, and obtained the particle size and the duration of time when the individual particle passed the sampling area. Then, utilizing two data the particle speeds are calculated. Firstly, measurements were carried out at Lac Blanc Pass in French Alps. Then, more precise measurements were conducted at the cold wind tunnel in NIED, which is 14 m long and its working section is 1 m x 1 m. Snow particle speed, its distribution with height and the relation to the wind speeds showed good agreement; the snow particle speed and the wind speed increased with height, and the former was always smaller than the latter below 1 m. In this manner, we succeeded to obtain the reliable snow particle speeds in the blowing snow for the first time and revealed its grain size dependence and the relation to the wind speeds. Similar trends were also shown with the random flight calculations; particle speeds are lower than the air speed. However, the differences in wind and particle speeds amounted larger in the simulation.
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