半干旱草地地表土壤热通量的计算及其对能量平衡的影响

Estimation of Ground Heat Flux for a Semi-Arid Grassland and Its Impact on the Surface Energy Budget

利用2008年7月兰州大学半干旱气候与环境观测(SACOL)站的观测资料,对比分析了地表土壤热通量的三种计算方法,即谐波法、温度预报校正法(TDEC法)以及结合自校正热通量板(HFP01SC)测量的温度积分法(ITHP法);进而分析了三种不同方法的计算结果对地表能量平衡的影响。比较5cm深度处谐波法和TDEC法的计算结果与HFP01SC的实测结果,三者的相位基本一致,相互之间均具有很好的线性关系;谐波法与TDEC法的计算值较为接近,但分别比HFP01SC的实测值偏大了2%和6%(主要发生在夜间)。对于地表的土壤热通量(G0),谐波法与TDEC法两者的计算结果仅偏差约1%;TDEC法与ITHP法的计算结果之间也具有很好的线性关系(R2=0.99),但偏差达到9%左右。相对于HFP01SC的实测结果,由谐波法和TDEC法计算的G0可将SACOL站的地表能量闭合率分别提高6%和7%左右;利用温度积分法将HFP01SC的实测结果校正到地表后,地表能量闭合率也提高了约6%。因此,在对涡动相关通量做了常规订正的情况下,当充分考虑了土壤热存储后,SACOL站的地表能量闭合率可提高6%～7%,达到82%～83%左右。

Three approaches,i.e.Harmonic analysis （HM） technique,temperature prediction-correction （TDEC） method and calorimetric method,for the estimation of ground heat flux are evaluated by using observations from the Semi-Arid Climate and Environment Observatory-of Lanzhou University （SACOL） in July 2008.The calorimetric method,which involves measurement by a HFP01SC self-calibrating heat flux plate buried at 5 cm depths and heat storage between the plate and the surface,was called as ITHP approach here.The results indicate that the good linear relationships were showed among the soil heat fluxes measured by the HFP01SC heat flux plate and those calculated from the HM technique and the TDEC method at 5 cm depths.The calculated soil heat fluxes from the latter two methods well follow the observed phase by the HFP01SC heat flux plate.The magnitudes of the soil heat flux calculated from the HM technique and the TDEC method are near to each other,while they are about 2% and 6% larger than the observed soil heat flux,respectively,which mainly occur at nighttime.Moreover,the ground heat fluxes calculated from the TDEC method and the HM technique are highly correlated with each other with R 2= 0.97,and their difference is only about 1%.The TDEC-calculated ground heat flux also has a good linear relationship with the ITHP-calculated ground heat flux with R 2=0.99,but their difference is larger （about 9%）.Furthermore,compared to the direct measurements by the HFP01SC soil heat plate at 5 cm depths,the ground heat flux calculated from the HM technique,the TDEC method and the ITHP approach can improve the surface energy budget closure by 6%,7% and 6% at SACOL site,respectively.Therefore,the contribution of the ground heat flux in the surface energy budget is very important for the semi-arid grassland ecosystem over the Loess Plateau in China.Using the turbulent fluxes after common corrections,soil heat storage between the surface and the heat flux plate can improve the surface energy budget closure by 6%～7%,resulting in a closure of 82%～83% at SACOL site.