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ESTIMATING ANNUAL APPARENT THERMAL DIFFUSIVITY IN PERMAFROST USING TEMPERATURE TIME SERIES ON THE QINGHAI-TIBET PLATEAU, CHINA
Session: Permafrost Degradation II / Dégradation du pergélisol II
Changwei Xie, Cold & Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences (China)
Gough William, University of Toronto-Scarborough (Toronto)
Lin Zhao, Cold & Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences (China)
Tonghua Wu, Cold & Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences (China)
Soil temperature data used in this study were obtained from 17 monitoring boreholes during the period from 2006 to 2010 on the Qinghai-Tibet plateau. Measurements show that the permafrost temperature is higher than -1.0°C at eleven sites and at eight sites it is higher than -0.5°C. We calculated the annual apparent thermal diffusivity (AATD) in permafrost at different horizons. Results indicate that the latent heat effects have important implications for the permafrost thermal regime. In warm permafrost regions, the latent heat effects buffered heat exchange and resulted in shallow depths of zero annual amplitude(DZAA) of ground temperature and AATD. At the same sites, thermal diffusivity is usually lower at the bottom of the active layer since ice-water conversion consumes most of heat exchange at this horizon. The thermal diffusivity is usually larger in the deep permafrost especially when the permafrost temperature is low. For the 17 monitoring boreholes, there is a causal relationship between the small AATD and the high permafrost temperature. The temperature-dependent adjustments of the thermal diffusivity have important implications for the warming trend of permafrost. The permafrost temperature gradient is greater in cold permafrost with large AATD than it is in warm permafrost with small AATD.
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