A frozen soil parameterization coupling of thermal and hydrological processes is used to investigate how frozen soil processes affect water and energy balances in seasonal frozen soil. Simulation results of soil liqui...A frozen soil parameterization coupling of thermal and hydrological processes is used to investigate how frozen soil processes affect water and energy balances in seasonal frozen soil. Simulation results of soil liquid water content and temperature using soil model with and without the inclusion of freezing and thawing processes are evaluated against observations at the Rosemount field station. By comparing the simulated water and heat fluxes of the two cases, the role of phase change processes in the water and energy balances is analyzed. Soil freezing induces upward water flow towards the freezing front and increases soil water content in the upper soil layer. In particular, soil ice obviously prevents and delays the infiltration during rain at Rosemount. In addition, soil freezingthawing processes alter the partitioning of surface energy fluxes and lead the soil to release more sensible heat into the atmosphere during freezing periods.展开更多
Based on the analysis of data on temperatures and moisture of soils in the active layer at four different permafrost sites in the source areas of the Yellow River(SAYR)in 2010–2012,the freeze–thaw processes of soils...Based on the analysis of data on temperatures and moisture of soils in the active layer at four different permafrost sites in the source areas of the Yellow River(SAYR)in 2010–2012,the freeze–thaw processes of soils in the active layer were compared and contrasted for understanding the spatiotemporal variations.At the four studied sites,the thickness and mean annual temperature of permafrost are different.The temperatures at the top of permafrost(TTOP),i.e.,the maximum depth(s)of seasonal frost and/or thaw penetration,are-1.9°C at the Chalaping site(CLP),-0.9°C at the site on the southern bank of the Zhaling Lake(ZLH),-0.4°C at the Maduo Town site(MDX),and 1.1°C at the site on the northern bank of the Eling Lake(ELH).Differences in the mean annual ground temperature of permafrost and TTOPs may be responsible for the differentiations in the freeze–thaw processes of soils in the active layer.With rising TTOPs,the ground thawing started earlier:CLP in early June,ZLH in late May,MDX in early May,and ELH in mid-April,while the freezing began later:CLP in early October,ZLH in early to midOctober,MDX in mid-October,and ELH in the mid-to late October.With increasing TTOPs,the freeze-up periods for permafrost sites were shortened:202 days at CLP,130 days at ZLH,100 days at MDX,and the period of complete thaw was 89 days at ELH.At the CLP and ZLH sites,the two-directional ground freezing(downwards from ground surfaces and upwards from the permafrost table)and thawing finished in the same year,but the ground freezing at the MDX continued to the end of the nextJanuary,with very slow freezing rates in the end.At the ELH site,ground freezing kept on until early May when thawing began on the surface,and upward and downward thawing became increasingly stable in late June to early July.At each site,with rising TTOPs,the downward freezing accelerated in comparison with the upward freezing,and with an increasing proportion of downward frozen depth,and with the larger ratios of freezing to thawing duration.In summary,the p展开更多
Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP).Under the background of temperature warming,the TP has witnessed an accelerated warming...Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP).Under the background of temperature warming,the TP has witnessed an accelerated warming trend in frozen ground temperature,an increasing active layer thickness,and the melting of underground ice.Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP,the trend of ground temperature at each observation site and its response to climate change were analyzed.The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period,the warming in winter is more significant than that in summer.The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites.During the study period,thawing occurred earlier,whereas freezing happened later,resulting in shortened freezing season and a thinner frozen layer at the BJ site.And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn.From 1997 to 2012,the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend,with a more significant temperature increase in winter than in summer.The ground temperature showed an obvious response to air temperature warming,but the trend varied significantly with soil depths due to soil heterogeneity.展开更多
Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size ...Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size groups, different water contents, various freeze-thaw cycles, and various freezing temperatures. The results showed that, when at suitable water content, aggregate stability was enhanced, aggregate sta-bility will be disrupted when moisture content is too high or too low, especially higher water content. Temperature also had a significant ef-fect, but moisture content determined the suitable freezing temperatures for a given soil. Water-stable aggregate （WSA〉0.5）, the total aggre-gate content, and mean weight diameter decreasing with the freeze-thaw cycles increase, reached to 5 percent significance level. The reason for crumbing aggregates is the water and air conflict, thus raising the hypothesis that water content affects the aggregate stability in the process of freezing and thawing.展开更多
基金supported by the National Basic Research Program of China under Grant No 2006CB400504National Natural Science Foundation of China under Grant Nos 40605027 and 40775050
文摘A frozen soil parameterization coupling of thermal and hydrological processes is used to investigate how frozen soil processes affect water and energy balances in seasonal frozen soil. Simulation results of soil liquid water content and temperature using soil model with and without the inclusion of freezing and thawing processes are evaluated against observations at the Rosemount field station. By comparing the simulated water and heat fluxes of the two cases, the role of phase change processes in the water and energy balances is analyzed. Soil freezing induces upward water flow towards the freezing front and increases soil water content in the upper soil layer. In particular, soil ice obviously prevents and delays the infiltration during rain at Rosemount. In addition, soil freezingthawing processes alter the partitioning of surface energy fluxes and lead the soil to release more sensible heat into the atmosphere during freezing periods.
基金supported by the National Natural Science Foundation of China (41301068)Global Change Research Program of China (2010CB951402)+1 种基金Excellent Youth Scholars Fund of Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences (51Y351051)Research Fund of State Key Laboratory of Frozen Soils Engineering (SKLFSE-ZQ-18)
文摘Based on the analysis of data on temperatures and moisture of soils in the active layer at four different permafrost sites in the source areas of the Yellow River(SAYR)in 2010–2012,the freeze–thaw processes of soils in the active layer were compared and contrasted for understanding the spatiotemporal variations.At the four studied sites,the thickness and mean annual temperature of permafrost are different.The temperatures at the top of permafrost(TTOP),i.e.,the maximum depth(s)of seasonal frost and/or thaw penetration,are-1.9°C at the Chalaping site(CLP),-0.9°C at the site on the southern bank of the Zhaling Lake(ZLH),-0.4°C at the Maduo Town site(MDX),and 1.1°C at the site on the northern bank of the Eling Lake(ELH).Differences in the mean annual ground temperature of permafrost and TTOPs may be responsible for the differentiations in the freeze–thaw processes of soils in the active layer.With rising TTOPs,the ground thawing started earlier:CLP in early June,ZLH in late May,MDX in early May,and ELH in mid-April,while the freezing began later:CLP in early October,ZLH in early to midOctober,MDX in mid-October,and ELH in the mid-to late October.With increasing TTOPs,the freeze-up periods for permafrost sites were shortened:202 days at CLP,130 days at ZLH,100 days at MDX,and the period of complete thaw was 89 days at ELH.At the CLP and ZLH sites,the two-directional ground freezing(downwards from ground surfaces and upwards from the permafrost table)and thawing finished in the same year,but the ground freezing at the MDX continued to the end of the nextJanuary,with very slow freezing rates in the end.At the ELH site,ground freezing kept on until early May when thawing began on the surface,and upward and downward thawing became increasingly stable in late June to early July.At each site,with rising TTOPs,the downward freezing accelerated in comparison with the upward freezing,and with an increasing proportion of downward frozen depth,and with the larger ratios of freezing to thawing duration.In summary,the p
基金the National Natural Science Foundation of China(41771068,41571066,41601077)the Strategic Priority Research Program of the Chinese Academy of Sciences(CAS)(XDA20100102)+1 种基金the Chinese Academy of Sciences(CAS)"Light of West China"Program,the Youth Innovation Promotion Association CAS(2018460)the Program of China Scholarship Council(201804910129).
文摘Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP).Under the background of temperature warming,the TP has witnessed an accelerated warming trend in frozen ground temperature,an increasing active layer thickness,and the melting of underground ice.Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP,the trend of ground temperature at each observation site and its response to climate change were analyzed.The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period,the warming in winter is more significant than that in summer.The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites.During the study period,thawing occurred earlier,whereas freezing happened later,resulting in shortened freezing season and a thinner frozen layer at the BJ site.And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn.From 1997 to 2012,the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend,with a more significant temperature increase in winter than in summer.The ground temperature showed an obvious response to air temperature warming,but the trend varied significantly with soil depths due to soil heterogeneity.
基金National Basic Research Program of China (2005CB121101, 2005CB121103)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-407)
文摘Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size groups, different water contents, various freeze-thaw cycles, and various freezing temperatures. The results showed that, when at suitable water content, aggregate stability was enhanced, aggregate sta-bility will be disrupted when moisture content is too high or too low, especially higher water content. Temperature also had a significant ef-fect, but moisture content determined the suitable freezing temperatures for a given soil. Water-stable aggregate （WSA〉0.5）, the total aggre-gate content, and mean weight diameter decreasing with the freeze-thaw cycles increase, reached to 5 percent significance level. The reason for crumbing aggregates is the water and air conflict, thus raising the hypothesis that water content affects the aggregate stability in the process of freezing and thawing.
