1.Key Laboratory of Land Surface Process and Climate Change in Cole and Arid Regions, Northwest Institute of Eco-Environment and Resource, Chinese Academy of Sciences, Lanzhou 730000;2.University of Chinese Academy of Sciences, Beijing 100049;3.College of Atmospheric Sciences, Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, Chengdu University of Information Technology, Chengdu 610225
Found by Foundation:National Natural Science Foundation of China Grants 41530529 91737103Found by Foundation:National Natural Science Foundation of China (Grants 41530529, 91737103)
准确量化高寒湿地下垫面冻结过程中土壤热通量的变化特征，对认识高寒湿地—大气间水热交换过程有重要的科学意义。本文利用中国科学院麻多气候与环境综合观测站2014年5月至2015年5月的观测资料，分析了下垫面冻结过程中土壤热通量变化特征，探讨了冻结潜热对土壤热通量的贡献。基于温度积分计算土壤热通量的算法，指出在计算冻结过程中的土壤热通量时，需要同时考虑土壤热通量板以上的土壤热贮存及热通量板以上的冻结潜热。研究表明：（1）冻结锋面形成后，锋面所在深度土壤体积含水量迅速降低，锋面以下土壤热通量接近于零，土壤液态水开始冻结，冻结潜热向上穿过热通量板所在土壤层；降水下渗土壤后冻结所释放的潜热能使次日凌晨5 cm深度土壤热通量接近于零。（2）季节性冻结期，凌晨气温较高时穿过5 cm土壤层的向上土壤热通量很小，可能是由表层土壤发生了日冻融循环所致。土壤水释放的冻结潜热使土壤温度波动减弱并维持在冰点附近。高寒湿地下垫面仅在很浅的表层发生日冻融循环，无法通过5 cm土壤温度资料判断下垫面循环出现日期。（3）加入冻结潜热项，土壤热通量的计算值与实测值之间的均方根误差将会从11.5 W m-2下降到6.2 W m-2。以上研究结果对认识寒区陆面过程有重要的贡献。
The accurate quantification of soil heat flux in the freezing process of the alpine wetland in the source area of the Yellow River has an important scientific significance for understanding the water and heat exchanges between alpine wetlands and the atmosphere. By using the field observed data collected from the Maduo climate and environment comprehensive observatory of the Chinese Academy of Sciences from May 2014 to May 2015, the characteristics of soil heat flux as the alpine wetlands froze were analyzed. The effect of the latent heat of fusion on soil heat flux was also discussed. Both the heat storage and latent heat of fusion loss from above the plate must be considered when calculating the soil heat flux at the alpine wetland using the simple measurement approach algorithm. If the latent heat of fusion is ignored, then large errors can be found. The main results are as follows. (1) After the freezing front appeared, soil heat flux at a depth below the freezing front decreases and approaches zero, the liquid water content of the soil at the depth of the freezing front decreases rapidly, and the soil below the freezing front froze. In addition, the freezing released latent heat travels upward through the soil layer where the soil heat flux plate is located and observed. As the precipitation infiltrates into the soil, thus releasing the freezing latent heat, the freezing latent heat causes the observed soil heat flux to approach zero at a depth of 5 cm. (2) During the seasonally freezing processes, upward soil heat flux at a depth of 5 cm approaches zero if there is a high temperature in the morning and at noon of the previous day. This phenomenon indicates the existence of a diurnal freezing-thawing cycle. The latent heat released by soil water can reduce the amplitude of soil temperature and keep the soil temperature near the freezing point. The diurnal freezing-thawing processes solely occur in a very shallow soil layer, making it difficult to ascertain whether the diurnal freezing-thawing cycle happened not just by using soil temperature data at a depth of 5 cm. (3) Considering the latent heat of fusion factor decreases the root mean square errors of soil heat flux between the observed and calculated values from 11.5 W m-2 to 6.2 W m-2. These findings can contribute towards a better understanding of the land surface processes in cold regions.
李光伟,文军,王欣,王作亮,贾东于,陈金雷.麻多高寒湿地冻结过程中土壤热通量变化特征分析.大气科学,2019,43(4):719~729 LI Guangwei,WEN Jun,WANG Xin,WANG Zuoliang,JIA Dongyu,and CHEN Jinlei.