天山巩乃斯河谷积雪深度及季节冻土温度对气温变化的响应

气候变化影响着积雪的时空变化和季节冻土的水热变化,同时积雪变化对季节冻土的水热状态也有着重要的影响。为了分析积雪和气温对季节冻土热状况的影响,本文使用基于TFACE原理的试验装置在天山积雪与雪崩研究站进行了野外空气增温控制试验。野外试验设置了三种处理：自然状态、增温Ⅰ和增温Ⅱ。自然状态为无人为干扰的纯自然状态,增温Ⅰ为距积雪或土壤表层10cm气温增温约2℃,增温Ⅱ为距积雪或土壤表层10cm气温增温约4℃。结果表明：气温增加对积雪消融有显著的影响。在初始雪深为128cm条件下,增温I和增温II处理下的积雪消融时间比自然状态下分别提前19天和25天。在融雪期,气温、最大雪深和最大雪深发生的日期是影响季节冻土温度的重要因子。积雪覆盖条件下,季节冻土从深层开始解冻。而积雪的消失使土壤直接接受太阳辐射,土壤温度则迅速升高,从而使增温I和增温II处理下的季节冻土提前解冻。积雪消失后,季节冻土解冻的方向是从表层开始逐渐到深层。若积雪深度超过100cm时,积雪和土壤交界面的热交换基本达到平衡,此时土壤热通量损失达到最小值。融雪水对土壤温度特别是深层未冻结土壤有制冷作用。停止增温后,三个室外试验处理下的土壤温度随着时间逐渐趋于一致,并且土壤温度随着气温的波动而显著变化。

Responses of Snow Depth and Seasonal Frozen Ground Temperature to Enhanced Air Temperature in Kunges Valley, Tianshan Mountains

Climate change is influencing the temporal and spatial variation of snow cover and the hydro-thermal variation of seasonal frozen ground. And both seasonal snow cover and frozen ground significantly affect the streamflow in spring and its annual distribution. In order to analyze the effects of snow cover and air temperature on the thermal regime of seasonal frozen ground, an air temperature enhancement experiment was performed at the Tianshan Station for Snow-cover and Avalanche Research with a temperature enhancement system based on the principle of Temperature Free-Air Controlled Enhancement(TFACE). The field experiment was conducted under three treatments: natural condition, temperature-enhanced treatment I (enhanced by approximately 2 ℃ ) and temperature-enhanced treatment II (enhanced by approximately 4 ℃ ). It began on March 13 and ended on April 15. The results indicate that the air temperature enhancement has greater impact on snow cover than on the seasonal frozen ground. With an initial snow depth of 128cm, snow-melting under the temperature-enhanced treatment I and treatment II are 19 days and 25 days respectively earlier than that under natural condition. Air temperature, maximum snow depth and its date are the key factors that influence the seasonal frozen ground temperature during the snow-melting season. Soil thaws from the bottom to the top soil layer under the condition of snow covering. Because of the disappearance of snow cover, the soil receives solar radiation directly and its temperature rises rapidly, which results in the advanced thaw of frozen soil under temperature-enhanced treatment I and treatment II. Besides, it thaws from surface to the bottom. When the snow depth is more than 100cm, the heat exchange on snow-earth interface is more or less balanced and the loss of soil heat flux is minimum. Snowmelt has cooling effect on soil temperature, especially the deep unfrozen soil layer. As the air temperature enhancement system shuts down, soil temperature under the three treatments gradually become identical with time and they change remarkably with the fluctuation of air temperature.