表碛下冰面消融的模拟与估算

Estimation of Ice Ablation under a Debris Cover

根据热传导理论和能量平衡原理建立了一个简单的数学模型,对表碛下冰面的融化热进行了估算.模型将表碛分为三层:第一层冰碛以剧烈的温度变化和夜间负温梯度的存在为特征;第二层为中间过渡层,温差和温度变化都较小;第三层为靠近下伏冰体的薄层冰碛,以温度低和变化稳定为特征.模型仅以地表温度时间序列、表碛厚度和导热系数、土壤热容量等参数为计算输入,即可对表碛不同层位的土壤温度及其下部冰体融化所需热量进行模拟估算.在科其喀尔冰川表碛区选取了3个具有不同表碛厚度的试验点(Spot1,0.8m;Spot2,1.5m;Spot3,2.1m)进行了模型测试.模型试验表明,模型对于不同厚度表碛下冰面融化热的模拟是较好的,然而对于不同层位地温序列的模拟仍有一定的偏差,造成这些偏差的原因主要是来自于模型假设和土壤温度垂向上的时间相位差.模拟结果同时也显示了不同表碛厚度下冰面消融的差异,冰面消融热平均分别为:Spot1:26.87W·m-2,Spot2:9.81W·m-2,Spot3:6.92W·m-2.

In this paper a simple numerical model is developed to estimate the ice ablation under a debris cover on the basis of heat transfer theory and energy conservation theory. To a given debris cover, three soil thermal layers are classified in the model. Debris layer 1 is characterized by an intense temperature vaxiation and a negative temperature gradient in the nighttime; within layer 2 the temperature is generally changing slowly; debris layer 3 is characterized by a low temperature and a feeble variation of the debris temperature. The model can calculate the temperatures of different interfaces with a given surface temperature, depth and thermal properties of the debris, and then calculate the heat for ice melting. A case study is carried out on the debris-covered area of Koxkar Glacier to the northwest of Tarim basin, to test the model. Three different spots with ice depths of 0 ^8 m (Spot 1), 1.5 m (Spot 2) and 2.1m (Spot 3), respectively, are selected in the examination. The case study shows that the model is relatively good for the estimation of heat that is consumed for ice ablation. For the debris temperature series of different depths, however, there is still an inconsistency between the simulated and observed values. The main reasons for this inconsistency might be attributed to the improper assumption in the simplified model and the phase lag in the vertical debris temperature profile. Estimation of ablation heat indicates a difference among the three spots. Heat for ablation under a debris cover is 26.87 W 5m -2 for Spot 1, 9.81 W 5m -2 for Spot 2 and 6.92 W 5m -2 for Spot 3, respectively.