Characteristics of ground freezing and thawing under snow cover based on long-term observation

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  • HARADA Yusuke
    The United Graduate School of Agricultural Sciences, Iwate University Snow Research Center
  • TSUCHIYA Fujio
    Obihiro University of Agriculture and Veterinary Medicine
  • TAKEDA Kazuo
    Obihiro University of Agriculture and Veterinary Medicine
  • MUNEOKA Toshimi
    Obihiro University of Agriculture and Veterinary Medicine

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  • 長期観測に基づく積雪下の土の凍結融解特性
  • チョウキ カンソク ニ モトズク セキセツ カ ノ ツチ ノ トウケツ ユウカイ トクセイ

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Abstract

Observations of frost and snow depths were conducted at the Obihiro University site located in eastern Hokkaido, Japan, from November 1981 to April 2007, and the characteristics of ground freezing and thawing under snow cover were analyzed. The results indicated that the annual maximum frost depth ranged from 5 to 55cm during the 26 winters. Frost depth is influenced by seasonal changes in snow depth, and it was confirmed that it is proportional to the square root of the freezing index when snow depth reaches 20cm. The thawing of frozen ground starts from the surface at the seasonal end of snow cover and finishes from late March to early May (last frost day). A linear relationship was found between the vanishing frost depth and the maximum frost depth. Further, the vanishing frost depth was found to be proportional to the square root of the thawing index. Based on these findings, the seasonal maximum frost depth, vanishing frost depth, and last frost day were calculated using meteorological data from 1961 to 1980 obtained from Obihiro Meteorological Observatory. Taken together, we can conclude that the annual maximum frost depth has decreased in the last half century and that the last frost day has shifted from mid to early April.

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