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九州大学北海道演習林の北向斜面と南向斜面において気温，積雪深，地温の連続測定を4冬季（2014 年－ 2018 年）にわたって行った。地温は深さ0 ～ 45cm において８深度で計測し，土壌凍結深度を地温の鉛直プロファイルから判断した。日平均気温は南向斜面よりも北向斜面で平均0.4°C 程度低かった。積雪は両斜面とも日平均気温が氷点下に転じた日以降に始まり，積雪直後は両斜面で積雪深に違いはなかった...。しかし，南向斜面では融雪速度が速いために，その後の積雪深は南向斜面で浅く，積雪の消失日は南向斜面で10 ～ 15 日ほど早かった。土壌凍結は，日平均気温が氷点下に転じた後に開始された。土壌凍結の開始前に積雪が生じると，土壌凍結の開始が１ヶ月程度遅れた。土壌融解は両斜面とも日平均気温が氷点を上回る前に起こり，北向斜面では積雪消失時期の半月以上前に土壌融解が開始される年もあった。最大土壌凍結深度は年変動するものの，北向斜面，南向斜面でそれぞれ15 － 35cm 程度，南向斜面で0 － 25cm 程度であり，南向斜面のほうが浅かった。
Air temperature, snow depth, and soil temperature on the north- and south-facing slopes of Ashoro Research Forest, Kyushu University Forest, were continuously measured over the four winter seasons from 2014 to 2018. Soil temperature was measured at eight depths from 0 cm to 45 cm depth and soil frost depth was evaluated from vertical profile of soil temperature. Mean daily air temperature was 0.4 °C lower on the north-facing slope than on the south-facing slope. Snow accumulation began after the day when mean daily air temperature was below the freezing point and the snow depth did not differ between north- and south-facing slopes just after the beginning of snow accumulation. However, the snow depth decreased on the south-facing slope more rapidly than on the north-facing slope due to rapid snow melting on the south-facing slope, causing 10-15 days faster for melting away of snow on the south-facing slope than on the north-facing slope. Soil frost began after the day when mean daily air temperature was below the freezing point. The start of soil frost was delayed about one month when the snow accumulation started before the start of soil frost. Soil melting occurred mostly on the day or a few days before when mean air temperature rose up over a freezing point. However, the soil melting on the north-facing slope in 2016 and 2017 began more than half a month before melting away of snow. Although annual maximum depth of soil frost varied, the depth was shallower on the south-facing slope (0-25 cm) than on the north facing slope (15-35 cm).show more
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