土壤热异常影响地表能量平衡的个例分析和数值模拟

摘要

首先给出了土壤热异常与短期气候变化的一个典型个例,进而基于一个off-line的陆面过程模式,通过改变进入土壤底层的热强迫,讨论了土壤热异常影响地表能量平衡过程可能的物理机制.在实验Ⅰ中,在土壤底层(6.3 m)引入5 W m-2的热通量积分3个月,发现与控制试验(土壤底部为零通量,即无热量的流入/流出)相比,地表仅有0.06℃的增温.实验Ⅱ在Ⅰ的基础上将土壤热传导系数放大一个等级以加速土壤中的热交换过程,发现地表增温可达0.65℃.若再将热强迫增至10 W m 2,则地表增温可达0.81℃,且地表感热通量的增幅可达约10 W m-2,这对短期气候变化已不可忽视.结果表明:当土壤热异常达到一定强度并且能较快上传时将对地表能量平衡过程产生明显影响.因此目前陆面过程模式中普遍忽略来自深部土壤热流的做法值得商榷.同时,客观地表述深部热流体在土壤中的传输过程及应用陆气耦合模式对深入理解这一问题也是必要的.%The statistical relationship between soil thermal anomaly and short-term climate change is presented based on a typical case study. Furthermore, possible physical mechanisms behind the relationship are revealed through using an off-line land surface model with a reasonable soil thermal forcing at the bottom of the soil layer.In the first experiment, the given heat flux is 5 W m-2 at the bottom of the soil layer (in depth of 6.3 m)for 3 months, while only a positive ground temperature anomaly of 0.06℃ can be found compared to the control run. The anomaly, however, could reach 0.65℃ if the soil thermal conductivity was one order of magnitude larger. It could be even as large as 0.81℃ assuming the heat flux at bottom is 10 W m-2. Meanwhile, an increase of about 10 W m-2 was detected both for heat flux in soil and sensible heat on land surface, which is not neglectable to the short-term climate change. The results show that considerable response in land surface energy budget could be expected when the soil thermal forcing reaches a certain spatial-tem poral scale. Therefore, land surface models should not ignore the upward heat flux from the bottom of the soil layer. Moreover, integration for a longer period of time and coupled land-atmosphere model are also necessary for the better understanding of this issue.