湿雪的密实化与颗粒粗化过程研究

研究了处于自然状态下的湿雪的密实化和颗粒粗化过程.在野外观测的基础上,通过应用粘滞流体模型,发现与干雪相反,当湿雪的含水率达到一定程度(重量含水率约5%)后,粘滞度随密度增加而降低.通过粒径量测与颗粒大小分布统计发现,与含水饱和的雪相同,在湿雪演变过程中,不同时刻的雪粒粒径积累频率分布曲线形状基本相同,且与含水饱和雪的基本一致,说明含水不饱和的雪与含水饱和的雪在颗粒粗化过程中具有相同的粒径分布及其演进特征.分析还显示,含水不饱和雪的颗粒粗化速率比含水饱和雪的小得多.

Densification and Grain Coarsening of Melting Snow

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/η_c, where ρ is density, t is time, σ is the load and η_c is the compactive viscosity. By using the observed data and regression, the function η_c (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.