Development of artificial surface hoar production system using a circuit wind tunnel and formation of various crystal types

摘要

The surface hoar layer is known to be one of the most typical types of weak layers in dry slab avalanches. To investigate the features of snow cover, including the surface hoar layer, we developed apparatuses that make surface hoar artificially. Two growth systems were developed using circuit wind tunnels. The first apparatus supplied wind using a circuit wind tunnel. A few millimeters thick of snow were placed on a cooling panel (0.12 m(2)) to form the fundamental snow layer. Surface hoar was then grown on the snow surface using the difference between the temperature and relatively high water vapor pressure of the air; and the cooled snow surface. The shapes of the artificially grown surface hoar crystals were simple plate, sector plate, dendrite, needle, column and cup. It was suggested that the crystal shape depended on snow surface temperature and wind condition. Both dendrite and needle shapes required low wind conditions. The trend of the temperature dependence of the crystal shape was often in agreement with the habit of artificial snow crystals and depth hoar crystals. In the second apparatus, we set nine cooling panels and made a surface hoar layer on the fundamental snow cover. It was possible to make surface hoar with an area of 1.08 m(2) with one experiment using this system. Three surface temperatures could be selected in a single experiment because the panels were cooled by three different thermostatic baths. These systems are useful for investigating the features of snow and the surface hoar layer efficiently.