Improving Ground Heat Flux Estimation: Considering the Effect of Freeze/Thaw Process on the Seasonally Frozen Ground
Jingyuan Wang, Siqiong Luo, Zhibang Lv, Wenjing Li, Xiaoqing Tan, Qingxue Dong, Zihang Chen
Abstract
Abstract An inadequate understanding of the changes in water and heat of the soil is likely a potential reason for the nonclosure of the surface energy balance. During the freeze/thaw period, the large volumetric heat capacity of ice and the latent heat of soil ice phase change had a specific influence on the estimation of ground heat flux ( G 0 ). However, the effects of the freeze/thaw process on G 0 estimation were not well quantified using field observations. The improvements of G 0 estimation by adding the soil ice heat storage (Δ s ice ) and the latent heat of soil ice phase change (Δ s LH ) were evaluated during the freeze/thaw period at two sites (Madoi and Maqu) on the eastern Tibetan Plateau. During the freeze/thaw period, both Δ s ice and Δ s LH had important influences on the reasonable determination of G 0 . Adding Δ s LH increased G 0 at the daytime peak by 34.4 W/m 2 (Madoi) and 9.3 W/m 2 (Maqu). During the completely frozen stage, the contributions of Δ s ice to G 0 ice + LH (adding both Δ s ice and Δ s LH ) were higher than those during other freeze/thaw stages at both sites, and Δ s LH also made a significant contribution to G 0 ice + LH . Therefore, the daily freeze/thaw cycles cannot be ignored during the completely frozen stage in the estimation of G 0 . The G 0 ice + LH approach improved the G 0 estimation more than G 0 ice (adding Δ s ice ) approach during the freezing and thawing stages. The improvements of G 0 estimations increased the energy closure status and reduced the daily average of imbalance.