青藏高原多年冻土区典型下垫面冻融过程作用分析

Analysis of Freezing and Thawing Processes on Typical Underlying Surface in Permafrost Area of Tibet Plateau

利用青藏高原腹地安多站土壤观测资料,根据10cm土壤日最高和最低温度将冻土分为融化过程、完全融化、冻结过程和完全冻结四个阶段,并结合感热通量、积雪深度、相对湿度和降水资料定性的探讨了冻融过程对地气热量、水分交换的影响。结果表明:各层土壤在东亚季风爆发前期由上至下完成融化过程,10月中旬~12月上旬完成冻结过程,融化期普遍长于冻结期。土壤湿度大值区在时间上集中在高原雨季,空间上10cm深度以上为湿度大值区,而且上层土壤的温度梯度要明显大于下层。在融化阶段整层土壤的温度长期保持0℃的等温相变现象,此时,表层土壤温度日变化幅度为全年最大,最高日变幅达22.5℃。安多站地面除12月个别天数和1月上旬是冷源外,全年为地面热源,近地面感热通量从1月开始增大,到6月上旬达到峰值,之后逐渐减小。同时,感热通量的变化对相对湿度、降水和积雪的变化较为敏感。

Based on the soil observation data of Amdo station in Tibet plateau, the peimafrost is divided into tour stages by the daily maximum and minimun soil temperature at 10cm depth： the thawing stage, the completely thawed stage,the freezing stage and the completely frozen stage. The ditterence between ground soil and air temperature （Ts -Ta） was analyzed and influence of freezing thawing process on the heat and moisture exchange was discussed by combining the freezing thawing action with the temperature, ground temperature, snow depth, relative humidity and precipitation data. The results show that： 1 ） Each layer of soil complete melting process from top to bottom beifore East Asian Monsoon. The freezing process completed from mid October to early December. The melting period is generally longer than the freezing period; 2）The soil humidity value area is concentrated in the rainy season, 10cm above the depth is the humidity value area. The temperature gradient above the soil is greater than below. In the melting stage, the isothermal phase transition of soil temperature is maintained at 0℃ for a long time. At the same time, the diurnal variation of soil surlace temperature was the largest in the whole year. The highest diurnal variation reached 22.5 degrees centigrade. 3 ） The （Ts - Ta） reached its peak in the early June, then decreased gradually, reaches the minimum value in early January, the annual change rate of 0℃ to 12℃. The change of temperature is sensitive to relative humidity, precipitation and snow cover.