HARDENING OF SNOW SURFACE--"NATURAL/ARTIFICIAL"

This paper describes two phenomena for the hardening of snow surface. One of them is natural hardening of snow surface by radiative cooling, which phenomenon is called "Shimi-watari" in Japanese. In Japan, people living in snowy regions have been enjoying such phenomenon for many years. Another is artificial hardening of snow surface. When snow festivals are held in early spring or in midsummer, snow surface was frozen by the use of sodium chloride (NaCl) preventing the snow surface from softening. This technique is the same as the arrangement of Alpine skiing racecourse by the use of "snow cement" or ammonium sulfate.