Improving Ground Heat Flux Estimation: Considering the Effect of Freeze/Thaw Process on the Seasonally Frozen Ground

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.