青藏高原深层土壤热通量的变化特征分析

Analysis of the Characteristics of Deep Soil Heat Flux in Qinghai-Tibetan Plateau

青藏高原地表热状况不仅对局地天气和气候变化有重要影响,而且还在次季节到季节尺度上对周边特别是下游地区的短期气候变化产生影响,因此日益受到研究者的关注。土壤热扩散率和土壤热通量是决定土壤热状况的两个重要因素。不同于以往的研究,本文利用青藏高原地区1980—2001年39个气象站0.8 m和3.2 m的土壤温度资料,采用热传导对流法计算了0.8~3.2 m深层土壤热扩散率和土壤热通量,分析了它们的年变化和年际变化特征,并分析了深层土壤热通量和高原季风的相关关系,得到了一些有意义的结论。青藏高原深层土壤温度随深度的增加振幅减小、位相延迟;在1980—2001年间,土壤热扩散率的变化总体呈减小趋势;土壤深层热通量年变化与土壤表层热通量的年变化具有相反的相位;总热通量与对流热通量的变化具有相同的相位;深层土壤热通量月平均值在冬季为负值(定义热流向上为正),夏季土壤热通量都为正值。土壤热通量与高原冬季风指数的变化趋势相反,相关系数为-0.53;而与高原夏季风指数变化趋势一致,相关系数为0.58,都通过了95%的显著性检验。这些结论对于促使我们认识高原陆气相互作用是非常有意义的。

The surface thermal condition of Qinghai-Tibetan Plateau is not only important for the local weather and climate,but also for the short-term climate change in the surrounding areas,especially in sub-seasonal to seasonal scale. Soil thermal diffusivity and soil heat flux are two key factors to determine soil thermal condition.The spatial and temporal distribution of soil thermal diffusivity and the soil heat flux in Qinghai-Tibetan Plateau are still not well understood. In this paper,the method of Conduction-Convection was applied to calculate the soil thermal diffusivity and the soil heat flux in Qinghai-Tibetan Plateau by using monthly mean soil temperature at the depths of 0. 8 m and 3. 2 m in 39 meteorological observatories from 1980 to 2001. Their characteristics of annual and inter-annual variations and the relationship between soil heat flux and plateau monsoon were analyzed and got some meaningful conclusions. The results showthat the annual amplitude of soil temperature decreases and phase of soil temperature delays with depth. The soil thermal diffusivity appears an overall decreasing trend from 1980 to 2001. The annual variations of soil heat flux have opposite phase between deep and surface. The annual variations of total heat flux and convective heat flux have the same phase. The monthly mean soil heat flux is negative during the winter,and positive in summer. The correlation coefficient between the soil heat flux and plateau winter monsoon index is-0. 53. The soil heat flux is consistent with the plateau summer monsoon index,the correlation coefficient between them is 0. 58. Both values pass the T-test with significance of α = 0. 05. These results are valuable for us to understand the plateau air-land interactions.