天山南坡科其卡尔巴契冰川度日因子变化特征研究

Study of the Positive Degree-day Factors on the Koxkar Baqi Glacier on the South Slope of Tianshan Mountains

度日模型是估算冰川消融的一种简单而有效的方法.根据科其卡尔巴契冰川2003年的观测资料,分析了该冰川度日因子的空间变化规律及其影响因素.研究表明:各高度上的度日因子,介于2.0～9.7mm·℃-1·d-1之间变化,平均值为5.7mm·℃-1·d-1,与青藏高原各冰川及其它地区冰川相比较小;随着海拔的增高,度日因子随之递增;随平均气温的升高而随之递减.由于冰面状况复杂,度日因子变化幅度较大,裸冰区的度日因子明显大于表碛覆盖区.人为测量误差、反照率、地形等对度日因子的影响也不容忽视.

The degree-day method is one of the simplest but sufficiently accurate schemes to estimate ablation on a glacier. It bases on linear correlation between ablation and sum of daily mean temperatures above melting point, which is called the positive degree-day sum (PDD) during a period. The factor linking the ablation to PDD is called the positive degree-day factor. Based on ablation and PDD, the degree-day factors are calculated. The degree-day factors range from 2.0 to 9.7 mm 5℃ + {-1 }·d + {-1 }, and its average value is 5.7 mm 5℃ + {-1 }·d + {-1 }. There are some factors influencing the degree-day factors on the Koxkar Baqi Glacier, including altitude, surface condition of the glacier, albedo and terrain. The study shows that: 1) The degree-day factor depends on altitude on the Koxkar Baqi Glacier; in general, the degree-day factor increases as altitude increases, then, the factor at higher altitude is larger than that at lower altitude, which is mainly due to the ablation caused by Absorbed global radiation at the high altitude, where the PDD is low due to low summer air temperature. 2) The degree-day factor of the Koxkar Baqi Glacier decreases as the mean temperature increases, as what observed in Dongkemadi Glacier, July 1 st Glacier, Yala glacier and AX010 Glacier 3) The surface condition of a glacier, including coverage of debris and snow, surface slope, and so on, is an important factor to the degree-day factor on the Koxkar Baqi Glacier. In the ablation area of the Koxkar Baqi Glacier, the zone below 3 900 m a.s.l. is covered with debris, and the zone above 3 900 m a.s.l. is debris-free; the depth of the debris varies from 0 to 250 cm in general. Debris has a strong influence on the surface energy balance and melting of the underlying ice. The surface debris layer works as a good insulator on the Koxkar Baqi Glacier. The factor in the debris-free area is larger than that in the debris-covered area, because of the main physical characteristics of the debris, such as the thermal resistance and albedo, which control the heat conduction to the ice-debris interface. It would be useful to understand the dependence of ablation on degree-day factor in the Koxkar Baqi Glacier, so that one can estimate the contribution of the Koxkar Baqi Glacier melting, using the degree-day method while calculating total discharge from the glacier basin.