青藏高原东部多、少雪年地表能量和水分特征对比研究

Comparative Analysis of Surface Energy and Water Characteristics in High Snowfall Years and Low Snowfall Years on the Qinghai-Xizang Plateau

青藏高原积雪对地表能量和水分交换有重要影响。本文通过选取青藏高原东部玛多、玛曲和垭口3个站点多雪年和少雪年的气象资料,对比分析了多雪年和少雪年的地表能量和土壤水热特征。结果表明:在地表辐射平衡方面,多雪年或积雪较多的时期可以反射掉较多的向上短波辐射。玛多站多雪年反射掉的向上短波辐射是少雪年的2.3倍,玛曲站主要积雪期(3-5月)中多雪时期比少雪时期多反射掉10.07 W·m^(-2)的向上短波辐射,垭口站多雪年的年平均向上短波辐射分别比两个少雪年高出37.49 W·m^(-2)和31.92 W·m^(-2)。多雪年或积雪较多的时期还可以减少向上长波辐射的发射。玛多站多雪年与少雪年向上长波辐射的差值在整个研究时段中基本为负,垭口站两个少雪年在当年12月初到次年1月和次年2月末到4月初这两个时段,积雪越深,向上长波辐射值越小。向上短波和向上长波辐射的差异使得多雪年的地表净辐射少于少雪年。不论多雪年还是少雪年,土壤热通量的值都很小,地表能量分配主要以感热通量和潜热通量为主。玛多站少雪年以感热通量为主且感热通量为正,但多雪年感热通量为负;玛曲站的3-5月,多雪年的降雪较少雪年集中,多雪年地表能量分配以潜热为主,少雪年地表能量分配以感热为主。两个站点多雪年土壤热通量由负转正的时间均晚于少雪年。由于积雪的保温效应,多雪年土壤温度高于少雪年,且地表温度与大气温度的差值较大,大气湿度的平均值也大于少雪年;土壤进入冻结期后,各个土层深度上土壤含水量随时间的改变减弱,玛多站在5 cm深度多雪年土壤含水量明显大于少雪年,玛曲站少雪年10~40 cm的土壤含水量变化更明显,垭口站20~160 cm各层土壤多雪年冻结时间晚于少雪年。

The snow cover on the Qinghai-Xizang Plateau has a significant effect on surface energy and water exchange. Based on the meteorological data of Madoi,Maqu and Yakou stations in the east of Qinghai-Xizang Plateau,this paper compares and analyzes the surface energy and water characteristics in high snowfall years and low snowfall years. The results show that:In terms of surface radiation balance,the years or periods with high snow can reflect more upward shortwave radiation. At Madoi station,the upward shortwave radiation which is reflected in the high snowfall year is 2. 3 times that in the low snowfall year. During the main snow period(from March to May)of Maqu station,10. 07 W·m-2upward shortwave radiation was reflected in the high snowfall period than in the low snowfall period. The mean upward shortwave radiation of yakou station in the high snowfall year was 37. 49 W·m-2and 31. 92 W·m-2higher than that in the low snowfall years,respectively. The high snowfall years or periods can also reduce the emission of upward long wave radiation. The difference of upward longwave radiation between high snowfall year and low snowfall year at Madoi station is basically negative during the whole study period. In the two low snowfall years of Yakou station,from December to January and from the end of February to the beginning of April,the deeper the snow was,the lower the upward long-wave radiation value was. Therefore,the difference between the upward shortwave radiation and the upward long wave radiation makes the surface net radiation in high snowfall years less than that in low snowfall years. The value of the soil heat flux is very small in both high and low snowfall years,and the surface energy distribution is mainly composed of sensible heat flux and latent heat flux. Madoi station is dominated by sensible heat flux in low snowfall year and it is positive. While the sensible heat flux is negative in high snowfall years. From March to May in Maqu,the snowfall is more concentrated in high snowfall year,and the surface energy distribution is mainly latent heat. At the same time,the surface energy distribution is mainly sensible heat in low snowfall year. The time of soil heat flux from negative to positive in high snowfall years is later than that in low snowfall years. Due to the heat preservation effect of the snow cover,the soil temperature and the difference between surface temperature and atmospheric temperature in high snowfall years is higher than that in low snowfall years,furthermore,the mean value of atmospheric humidity is also higher than that in low snowfall years. After the soil entering the freezing stage,the change of soil moisture in each layer decreases with time. At the depth of 5 cm,the soil moisture in high snowfall years was significantly higher than that in low snowfall years. At Maqu station,the variation of soil moisture at 10 cm to 40 cm is more obvious in low snowfall years. For the soil freezing time 20~160cm in Yakou station,the high snowfall year is later than the low snowfall year.