Long-term variations and trends in the annual maximum snow depth and snow cover duration were analyzed for Niigata Prefecture between the winters of 1941/42 and 2012/13. Analysis was conducted on ...daily snow depth data from 17 snow observation sites, ranging in altitude from 4m to 507 m, and both the simple linear regression analysis and the Mann-Kendall test were utilized as means to detect trends. Statistical significance of the trend in this study was evaluated at a level of significance of 5%. The results showed that the annual maximum snow depth is on a decreasing trend in the plain area, which has an altitude of 30m or less, while no significant trend is seen in the mountainous area. The rates of decrease range from 2.3 to 12.8cm every 10 years. It is considered that decreases in winter precipitation and rises in winter temperature are likely to be related to the decreasing trend in the annual maximum snow depth. In addition, a decreasing trend in the snow cover duration was observed at the stations analyzed in this study, which have an altitude of 350m or less; rates of decrease range from 1.7 to 7.5 days every 10 years. In the plain area at an altitude of 30m or less, this decreasing trend is believed to be primarily due to the significant increase in air temperature in February and March.
The release mechanism of snow avalanches depends on the mechanical properties of snow, which are closely related to snow microstructure. Previous observations show that snow microstructure can be ...described qualitatively on the basis of snow types. However, the qualitative determination of snow types may become subjective. Therefore, it is essential to quantitatively classify snow. The specific surface area (SSA) and intrinsic permeability (
k
0) are closely related to the snow microstructure. In particular, we believe that the former parameter reflects the features of the grains, and the latter parameter indicates the characteristics of the pores. Measurements of the specific surface area per unit snow volume (
SSAV) and the intrinsic permeability were performed on the naturally deposited dry snow in Hokkaido prefecture, Japan, during the winter of 2007–2008.
SSAV was measured using a stereological method, where the section planes of snow samples were prepared, imaged, and analyzed, and the SSA per unit mass (
SSAM) was obtained by dividing
SSAV by the snow density. The value of
SSAV indicates only the area size, while the value of
SSAM indicates the snow microstructure.
k
0 was measured in situ using an air permeameter with a double cylinder, and it was calculated assuming a laminar flow in order to satisfy Darcy's law. The results showed that the correlation between
SSAM and
k
0 could be used to clearly distinguish the snow types. In addition, we could confirm certain changes in
SSAM and
k
0 accompanied by the occurrence of the two processes of temperature gradient and melt-freezing metamorphism, which occur in the snow cover.
