ZHOU Shi-qiao, NAKAWO M, HASHIMOTO S, SAKAI A, NARITA H, ISHIKAWA N
Extensive studies have been reported on the densification of dry snow, but few have been done in the densification of natural wet snow. This paper deals with the densification and grain coarsening of melting snow. A fieldwork was conducted at Moshiri, in the northern part of Hokkaido, Japan, from March to April in 1998. The work included intensively and successively snow sampling, taking snow grain photos, recording snow and air temperature, as well as measuring water content. Based on the stratigraphical records, the snow pack can be divided into 5 layers. For the surface layer, there was a daily melting freezing process in the melting season. For the bottom layer, its thickness varied with location of pit by several centimeters because of landform fluctuations and a slight bottom melting due to heat flux from the earth. Therefore only the three intermediate layers, which were 16 5 cm (LB), 38 cm (LC) and 24 cm (LD) in thickness respectively at the beginning of the fieldwork, were chosen. These three layers kept a constant temperature of 0℃ and certain water content in the study period. By regarding the snow as a viscous fluid, the following model is used: 1/ρdρ/dt=σ/ηc, where ρ is density, t is time, σ is the load and ηc is the compactive viscosity. By using the observed data and regression, the function ηc (ρ) is obtained. It is found that, the snow compactive viscosity decreases with density increase, which is opposite to the trend of dry snow. Compared with Kojimas data[25], it can be seen that the difference arises from the higher water content and grain coarsening. Based on the measurement of snow grain size, it is also found that, similar to the water saturated snow, the frequency of particle size at different times almost all have the same distribution. This reveals that the water unsaturated melting snow holds the same particle coarsening behavior as the water saturated snow does. It is shown that the water unsaturated melting snow coarsens much more slowly than the water saturated snow. The C value, which is the viscosity when the snow density is zero, is related to the mean particle size. It shows that the C value decreases with particle size increasing. It is also found that the decreasing rate of C value increases with grain coarsening rate decrease.