祁连山典型大陆型冰川近地层湍流参数与消融物理过程研究

Glacial runoff is vital supplies for the water use of production and life in the western arid and semi-arid regions of China, and under the global warming background, the physical process simulation of glacial ablation become the difficult and hot issues of Glaciology. Surface energy balance of the glacier is one of important methods for glacial ablation research, and the uncertainty of turbulent parameters restricts the credibility of the model. In the typical continental glacier of the Qilian Mountains (the Laohugou Glacier No.12), the observation of weather station and eddy-covariance system are carried out, and surface energy model is improved and the accurate simulation of glacial ablation is finished. The main researches are as follows: 1) The turbulent fluxes calculated by bulk aerodynamic method will be corrected by those observed from eddy-covariance system, and accurate surface roughness and bulk transfer coefficient are obtained. 2) Based on the turbulent parameters, surface energy balance model will be improved and the process of glacial ablation is simulated, which results will be validated by the measured deduced from the sonic ranging sensors and the stakes data. 3) Based on the glacial ablation simulation, the force influences of glacial ablation by dust will be quantified through the observed change of albedo. 4) Climate sensitivity test will discuss how the continental glacier responds to climate change under different settings. Based on the above research, the processes of glacial ablation will be understood from a physical mechanism, to lay the foundation for the quantitative evaluation of the changes of glacial runoff and the changes of glacier water resources in the Qilian Mountains.

冰川融水是我国西部干旱半干旱区生产生活用水的重要补给，全球变暖背景下冰川消融过程的模拟研究是目前冰川学的难点和热点。冰川表面能量平衡模型是研究冰川消融过程的重要方法之一，其中湍流参数的不确定性制约模型可信度。本项目拟在祁连山典型大陆型冰川（老虎沟12号冰川）开展气象和涡动相关系统观测，改进能量平衡模型，准确模拟冰川表面消融过程。包括以下工作：1）利用湍流通量的观测值标定整体空气动力学法，获取准确地表粗糙度和总体输送系数；2）以此为基础，改进能量平衡模型，模拟冰川消融过程，并以气象站雪深资料和花杆观测资料加以校验；3）在冰川消融模拟的基础上，通过冰川表面反照率变化定量计算粉尘对冰川消融的强迫作用；4）通过敏感性试验，探讨大陆型冰川在不同情境下对气候变化的响应过程。以上工作将有助于从物理机制上理解冰川消融过程，并为未来定量评估冰川融水径流变化及水资源奠定基础。

能量平衡模型建立了冰川与大气之间的联系，冰川是气候变化的产物，在气候变暖背景下开展冰川消融模拟工作，对于探讨冰川对气候变化的响应以及评估未来水资源变化具有重要的意义。项目依托中国科学院祁连山站，基于2010-2017年自动气象站观测数据，结合能量平衡模型，在老虎沟12号冰川开展了冰川消融模拟工作。结果表明，（1）积累区和消融区冰川表面空气动力学粗糙度月平均值分别介于0.6～ 2.4mm和1.3-7.8mm之间，大气层结稳定时，动量拖曳系数和热量输送系数月平均值都介于0.0008 - 0.0013之间，大气层结不稳定时，介于0.0021- 0.0022间；（2）净短波辐射是消融区冰川表面的主要能量来源（129 W m-2/96%），感热通量仅为5.7 W m-2（占4%）；冰川消融耗热是第一能量支出项（82.5 W m-2/61%），其次才是净长波辐射（46 W m-2/34%），潜热通量最小，仅占5%；（3）12号冰川海拔4550米处冰川物质平衡模拟值达到12615 mm w.e.，超过观测值505 mm w.e.，这个差值小于花杆观测值的均方根误差568 mm w.e.，可以看出，SEB模型在模拟冰川消融变化方面还是有很好的可行性。（4）观测的6年期间，吸光性物质导致冰川表面辐射强迫年均值达到1.9-4.6 W m-2，冰川强迫消融量增加了1101-2663 mm w.e.，占到了冰川总消融量的8.2-22.3%。（5）由于吸光性物质的存在，纯冰反照率设定为0.3和0.4时，冰川近地层气温强迫增加1.3和3.2℃所造成的冰川消融量与之相当。（6）当冰川反照率变化20%时，导致冰川物质平衡变化值达到46%，仅相当于向下短波辐射变化10%导致的冰川物质变化数值。以上结果也验证了空气动力学法在计算冰川表面湍流通量中具有很好的可信性，能量平衡能够很精确的模拟冰川消融变化，由于吸光性物质的存在，降低了冰川表面反照率，导致辐射强迫增加和冰川消融量增加，这也为未来在流域尺度上开展冰川消融工作奠定了基础。