Thawing and freezing processes of active layer in Wudaoliang region of Tibetan Plateau |
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Authors: | Lin Zhao Guodong Cheng Shuxun Li Xinmin Zhao Shaoling Wang |
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Institution: | (1) State Key Laboratory of Frozen Soil Engineering, Institute of Cold and Arid Regions Environmental and Engineering Research, Chinese Academy of Sciences, 730000 Lanzhou, China |
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Abstract: | The interaction between permafrost and atmosphere is accomplished through transfer of heat and moisture in the overlay active
layer. Thus, the research on the thermal and hydrodynamics of active layer during the thawing and freezing processes was considered
a key to revealing the heat and moisture exchanges between permafrost and atmosphere. The monitoring and research on active
layer were conducted because permafrost occupies about two thirds of the total area of the Tibetan Plateau. Based on the analysis
of the ground temperature data and soil moisture data of monitoring near the Wudaoliang region of the Tibetan Plateau, the
thawing and freezing processes of active layer were divided into four stages, i.e. summer thawing stage (ST), autumn freezing
stage (AF), winter cooling stage (WC) and spring warming stage (SW). Coupled heat and water flow is much more complicated
in ST and AF, and more amount of water is migrating in these two stages. Heat is transferred mainly via conductive heat flow
in the other two stages, and less water migrated. Four water migration and coupled heat flow processes were addressed for
the thawing and freezing stages, which are water infiltration driven by gravity, moisture advection and distillation driven
by temperature and osmotic gradients, water migration driven by capillarity and unfrozen water migration driven by temperature
gradient. The water content near the permafrost table tends to increase after one thawing and freezing cycle, which is the
main reason for the development of thick ground ice layer near permafrost table. |
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Keywords: | active layer freezing process water heat couple |
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