Basic Researches on Snowmelt Processes in a Subalpine Region

从热量平衡的角度研究了亚高山地区的融雪特征。新的解释是：（1）净辐射在融雪能量中的比例随着时间的推移而减少，这是因为潜热传输导致了融化季节后半段的凝结。凝结加速了雪的融化。另一方面，蒸发发生在上半年，抑制了融雪。(2)当潜热输送为负值且发生蒸发时，坡面和平地的融雪速率差异是由两个研究点净辐射的变化引起的。当凝结发生时，湍流通量对坡度引起的融雪差异的影响不可忽略。坡度与平地间的融雪差异随风速差的增大而增大。(3)在融化季节的前半段，较低的地方的融雪速率大于较高的地方。但在后半期，较高位置的融雪速度加快。随着时间的推移，低海拔地区的辐射能量总是大于高海拔地区，而高海拔地区的湍流热量输送则逐渐增加，尤其是在温暖多风的天气里，湍流热量输送的变化对亚高山地区的融雪特性非常重要，因为融雪季节很长。

Snowmelt characteristic in a subalpine region were investigated from a viewpoint of a heat balance. New interpretations obtained by this project are as follows ; (1) Ratios of net radiation in snowmelt energy decreased as time passed, because latent heat transfer caused a condensation in the latter half of the melting seasons. The condensation accelerates snowmelt. On the other hand, evaporation occurred in the first half and restrains snowmelt. (2) Differences of snowmelt rates between a slope and a flat place were caused by variations of net radiation at the two study point, when latent heat transfer was negative values and evaporation occurred. The influence of turbulent flux on differences of snowmelt caused by a slope angle was not ignored, when condensation occurred. Differences of snowmelt between a slope and a flat place increased with the increase of differences of wind speed between them. (3) Snowmelt rates were larger at a lower place than at a higher place in the first half of the melting seasons. But snowmelt at the higher place was accelerated during the latter half. Radiative energy was always larger at the lower site than at the higher site, and turbulent heat transfer increased at the higher site as time passed, especially on warm and windy days.Variabilities of turbulent heat transfer are very important on snowmelt characteristics at a subalpine region, because melting seasons are very long.