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Impacts of Freeze/Thaw Processes on Land Surface Energy Fluxes in the Permafrost Region of Qinghai-Xizang Plateau


Plateau Meteorology


Ge Jun, Yu Ye, Li Zhenchao, Xie Jin, Liu Chuan, Zan Beilei









Corresponding Author

Yu, Y

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Permafrost; Freeze/thaw processes; Land surface energy fluxes; Bowen ratio


Permafrost is ubiquitous on the Qinghai-Xizang Plateau. Soil freezing/thaw processes change the surface condition,which significantly influences the material and energy exchange between land and atmosphere. Observational data of land surface processes from the National Basic Research Program of ChinaThe response of desertification over Tibet Plateau to global changesat Beiluhe during 2014 2015 were used in this paper. The permafrost is divided into four stages based on the daily maximum and minimum soil temperature at 5 cm depth,i.e. the thawing stage,the completely thawed stage,the freezing stage and the completely frozen stage. Characteristics of the seasonal and diurnal variations of surface sensible heat flux(Hs),latent heat flux(LE), ground soil heat flux(G_0)and Bowen ratio at different freeze/thaw stages are analyzed and the impacts of freeze/ thaw processes on land surface energy fluxes and energy partitioning are investigated. The results show that: the transition of soil freeze/thaw stages has remarkable effect on the seasonal variations of Bowen ratio and G_0. Bowen ratio decreases and G_0 changes from positive to negative at the beginning of the completely thawed stage and conversely when the soil starts to freeze. The impact of freezing process on the trend of Hs and LE is not obvious but Bowen ratio increases significantly. Thawing process leads to the reduction in Hs and increase in LE,which makes Bowen ratio decrease obviously. The diurnal variation of Hs is similar during different stages. The diurnal variation of LE is related to the near surface soil water content and its diurnal variation. Due to weak diurnal variation, the higher soil water content leads to larger LE during completely frozen and thawed stages. LE is constrained during the freezing and thawing stage by the combined effects of the large diurnal variation of soil water content and the out-of-phase changes of soil water content and R_(net). Influenced by freeze/thaw processes,the diurnal variation of G_0 is weak during the freezing stage.