Observations and a Theory of Temperature Profiles in a Surface Layer of Snow Cooling through Nocturnal Radiation

Abstract

Temperature profile and its change with time in a snow surface layer cooling through nocturnal radiation is measured by thermometers of minute thermistor elements (fig. 1). Thermal diffusivity is calculated from the change with time of temparature profile by Takahashi's graphical method of solution for the problems of heat conduction (fig. 3), and the value of 0.00276cm²/sec is obtained (measured snow density is 0.15). The lowest temperature is observed at a depth of about 0.7cm under the surface (fig. 5). This feature of the profile is attributable to semi-transparency of snow layer, and is also demonstrated theoretically, assuming that radiation takes place in the snow layer down to a certain depth (fig. 7). In the case when heat transfer between snow and air is small due to weak turbulence of air the surface of snow is kept at the lowest temperature. As to the compensation for the remarkable temperature fall of the snow surface layer (fig. 8) will be discussed later.