| Summary: | Reports Canadian Defence Research Board's study, 1950-54. Experiments on rates of freeze and thaw of the active layer are described, showing the effects of surface cover, snow cover and characteristics determining the ability of the soil to conduct and absorb heat. Soil temperatures at varying depths were obtained at stations in swamp and high, dry areas of forested and non-forested localities by means of copper-constantan thermocouples and a portable potentiometer. Snow depth, water level measurements and snow temperatures were recorded for part of the time. Correlations between ambient air temperatures and soil temperatures at varying depths and with varying moisture content, ground and snow covers are presented in graphic and tabular form and discussed; also changes in snow temperature at different depths. Findings show a lag, increasing with depth and longest in relatively dry areas, of soil temperature behind ambient air temperatures; and variations in the effect of snow cover according to its hardness, moisture content and depth. The thermal gradient of the snow is affected by changes in temperature of the ambient air and of the soil, ice or water below it.
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