The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO i...The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH： warmer SST in the TIO changes the equivalent potential temperature （EPT） in the atmospheric boundary layer （ABL）, alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.展开更多
In this paper, a practical equivalent circuit of an active flux-controlled memristor characterized by smooth piecewise-quadratic nonlinearity is designed and an experimental chaotic memristive circuit is implemented. ...In this paper, a practical equivalent circuit of an active flux-controlled memristor characterized by smooth piecewise-quadratic nonlinearity is designed and an experimental chaotic memristive circuit is implemented. The chaotic memristive circuit has an equilibrium set and its stability is dependent on the initial state of the memristor. The initial state-dependent and the circuit parameter-dependent dynamics of the chaotic memristive circuit are investigated via phase portraits, bifurcation diagrams and Lyapunov exponents. Both experimental and simulation results validate the proposed equivalent circuit realization of the active flux-controlled memristor.展开更多
Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well,to diagnose the production state,and to optimize the management o...Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well,to diagnose the production state,and to optimize the management of draining and collection of coalbed methane.A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin,based on the results of isothermal adsorption experiments,and an analytical model was developed based on the Langmuir sorption theory.With the model,a numerical method that adopts equivalent desorption rate and its curve was established,which can be used to characterize the staged desorption of coalbed methane.According to the experimental and numerical characterizations,three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage,have been proposed and confirmed,namely,start-up pressure,transition pressure and sensitive pressure.By using these three key pressure points,the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages,i.e.,zero desorption stage,slow desorption stage,transition desorption stage,and sensitive desorption stage.According to analogy analysis,there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production.Moreover,it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage,whereas it is also possible that the declining production stage may occur ahead of schedule.展开更多
Highly accurate observations at various scales on the land surface are urgently needed for the studies of many areas,such as hydrology,meteorology,and agriculture.With the rapid development of remote sensing technique...Highly accurate observations at various scales on the land surface are urgently needed for the studies of many areas,such as hydrology,meteorology,and agriculture.With the rapid development of remote sensing techniques,remote sensing has had the capacity of monitoring many factors of the Earth's land surface.Especially,the space-borne microwave remote sensing systems have been widely used in the quantitative monitoring of global snow,soil moisture,and vegetation parameters with their all-weather,all-time observation capabilities and their sensitivities to the characteristics of land surface factors.Based on the electromagnetic theories and microwave radiative transfer equations,researchers have achieved great successes in the microwave remote sensing studies for different sensors in recent years.This article has systematically reviewed the progresses on five research areas including microwave theoretical modeling,microwave inversion on soil moisture,snow,vegetation and land surface temperatures.Through the further enrichment of remote sensing datasets and the development of remote sensing theories and inversion techniques,remote sensing including microwave remote sensing will play a more important role in the studies and applications of the Earth systems.展开更多
A reliability assessment method of fatigue life based on the long-term monitoring data is developed for welded details in steel box girder,and the application research is presented with examples of welded rib-to-deck ...A reliability assessment method of fatigue life based on the long-term monitoring data is developed for welded details in steel box girder,and the application research is presented with examples of welded rib-to-deck details in Runyang Bridges. Firstly the fatigue damage limit-state function is established based on S-N curves and Miner's rule,and the probability distribution characteristics of the coefficients in the function are discussed in detail. The uncertainties in fatigue loading effects are mainly studied based on long-term monitoring data. In the traditional studies,only the uncertainty of equivalent stress range is considered in fatigue reliability assessment. However,stress cycle number is also treated as a random variable in this paper because we know traffic flow every day differs in a thousand ways. Then the optimization method is employed to calculate the fatigue reliability. After studying the changing law of the reliability indices with time and the effect of the randomness of stress cycle number on reliability,the effect of the traffic growth on the reliability is studied. This study shows that the uncertainty in the fatigue life of the welded details can be well studied based on structural health monitoring,so it is necessary to carry out long-term strain monitoring of the welded details for accurate fatigue reliability assessment during the whole service period.展开更多
Based on the characteristics of fractured vuggy porous media,a novel mathematical model was proposed to model fluid flow in such media on fine scale,i.e.,the discrete fracture-vug network model.The new model consists ...Based on the characteristics of fractured vuggy porous media,a novel mathematical model was proposed to model fluid flow in such media on fine scale,i.e.,the discrete fracture-vug network model.The new model consists of three systems:porous rock system,fracture system,and vug system.The fractures and vugs are embedded in porous rock,and the isolated vugs could be connected via the discrete fracture network.The flow in porous rock and fractures follows Darcy's law,and the vugs system is free fluid region.Using a two-scale homogenization limit theory,we obtained a macroscopic Darcy's law governing the media on coarse scale.The theoretical formula of the equivalent permeability of the fractured vuggy porous media was derived.The model and method of this paper were verified by some numerical examples.At the end the permeability of some fractured vuggy porous media with typical fracture-vug structures was analyzed.展开更多
Multi-terminal direct current(MTDC)grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy.The modular mul...Multi-terminal direct current(MTDC)grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy.The modular multilevel converter(MMC)has become the basic building block for MTDC and DC grids due to its salient features,i.e.,modularity and scalability.Therefore,the MMC-based MTDC systems should be pervasively embedded into the present power system to improve system performance.However,several technical challenges hamper their practical applications and deployment,including modeling,control,and protection of the MMC-MTDC grids.This paper presents a comprehensive investigation and reference in modeling,control,and protection of the MMC-MTDC grids.A general overview of state-of-the-art modeling techniques of the MMC along with their performance in simulation analysis for MTDC applications is provided.A review of control strategies of the MMC-MTDC grids which provide AC system support is presented.State-of-the art protection techniques of the MMCMTDC systems are also investigated.Finally,the associated research challenges and trends are highlighted.展开更多
The surface deformation after fully mechanized back filling mining was analyzed.The surface deformation for different backfill materials was predicted by an equivalent mining height model and numerical simulations.The...The surface deformation after fully mechanized back filling mining was analyzed.The surface deformation for different backfill materials was predicted by an equivalent mining height model and numerical simulations.The results suggest that:(1) As the elastic modulus,E,of the backfill material increases the surface subsidence decreases.The rate of subsidence decrease drops after E is larger than 5 GPa;(2) Fully mechanized back fill mining technology can effectively control surface deformation.The resulting surface deformation is within the specification grade I,which means surface maintenance is not needed.A site survey showed that the equivalent mining height model is capable of predicting and analyzing surface deformation and that the model is conservative enough for engineering safety.Finally,the significance of establishing a complete error correction system based on error analysis and correction is discussed.展开更多
Human activity intensity is a synthesis index for describing the effects and influences of human activities on land surface. This paper presents the concept of human activity intensity of land surface and construction...Human activity intensity is a synthesis index for describing the effects and influences of human activities on land surface. This paper presents the concept of human activity intensity of land surface and construction land equivalent, builds an algorithm model for human activity intensity, and establishes a method for converting different land use/cover types into construction land equivalent as well. An application in China based on the land use data from 1984 to 2008 is also included. The results show that China＇s human activity intensity rose slowly before 2000, while rapidly after 2000. It experienced an increase from 7.63% in 1984 to 8.54% in 2008. It could be generally divided into five levels： Very High, High, Medium, Low, and Very Low, according to the human activity intensity at county level in 2008, which is rated by above 27%, 16%-27%, 10%-16%, 6%-10%, and below 6%. China＇s human activity intensity was spatially split into eastern and western parts by the line of Helan Mountains-Longmen Mountains-Jinghong. The eastern part was characterized by the levels of Very High, High, and Medium, and the levels of Low and Very Low were zonally distributed in the mountainous and hilly areas. In contrast, the western part was featured by the Low and Very Low levels, and the levels of Medium and High were scattered in Gansu Hexi Corridor, the east of Qinghai, and the northern and southern slopes of Tianshan Mountains in Xinjiang.展开更多
The regional satellite navigation system of COMPASS (Phase I) provides both open services and authorized services. Authorized services offer differential corrections and integrity information to users to support highe...The regional satellite navigation system of COMPASS (Phase I) provides both open services and authorized services. Authorized services offer differential corrections and integrity information to users to support higher positioning, navigation and timing precision. Experimenting with real data, positioning accuracy is estimated with a 3GEO/4IGSO COMPASS constellation. The results show that with dual-frequency and single-frequency pseudo-range measurements, the positioning errors are respectively 8 and 10 m (RMS) for open service users, while for authorized users, the errors are 4 and 5 m (RMS), respectively. The COMPASS constellation geometry may cause large error to occur in the height component by 7-9 m for dualor single-frequency users, which can be effectively reduced with the differential corrections supplied by the authorized services. Multipath errors are identified and corrected for COMPASS, resulting in 25% positioning accuracy improvement for dual-frequency users and 10% improvement for single-frequency users.展开更多
The flow resistance factors of non-submerged rigid vegetation in open channels were analyzed. The formulas of drag coefficient CD and equivalent Manning＇s roughness coefficient na were derived by analyzing the force ...The flow resistance factors of non-submerged rigid vegetation in open channels were analyzed. The formulas of drag coefficient CD and equivalent Manning＇s roughness coefficient na were derived by analyzing the force of the flow of non-submerged rigid vegetation in open channel. The flow characteristics and mechanism of non-submerged rigid vegetation in open channel were studied through flume experiments.展开更多
Northeastern China has the second largest expanse of permafrost in China,primarily known as Xing'an-Baikal permafrost.Located on the southeastern edges of the Eurasian cryolithozone,the permafrost is thermally uns...Northeastern China has the second largest expanse of permafrost in China,primarily known as Xing'an-Baikal permafrost.Located on the southeastern edges of the Eurasian cryolithozone,the permafrost is thermally unstable and ecologically sensitive to external changes.The combined impacts of climatic,environmental,and anthropogenic changes cause 3-dimensional degradation of the permafrost.To predict these changes on the southern limit and ground temperature of permafrost in Northeastern China,an equivalent latitude model (ELM) for the mean annual ground surface temperature (MAGSTs) was proposed,and further improved to take into account of the influences of vegetation and snow-cover based on observational data and using the SHAW model.Using the finite element method and assuming a climate warming rate of 0.048°C a-1,the ELM was combined with the unsteady-state heat conduction model to simulate permafrost temperatures at present,and to predict those after 50 and 100 a.The results indicate that at present,sporadic permafrost occurs in the zones with MAGSTs of 1.5°C or colder,and there would still be a significant presence of permafrost in the zones with the present MAGSTs of 0.5°C or colder after 50 a,and in those of-0.5°C or colder after 100 a.Furthermore,the total areal extent of permafrost would decrease from 2.57×105 km2 at present to 1.84×105 km2 after 50 a and to 1.29×105 km2 after 100 a,i.e.,a reduction of 28.4% and 49.8% in the permafrost area,respectively.Also the permafrost would degrade more substantially in the east than in the west.Regional warming and thinning of permafrost would also occur.The area of stable permafrost (mean annual ground temperature,or MAGT≤-1.0°C) would decrease from present 1.07×105 to 8.8×104 km2 after 50 a,and further decrease to 5.6×104 km2 after 100 a.As a result,the unstable permafrost and seasonally frozen ground would expand,and the southern limit of permafrost would shift significantly northwards.The changes in the permafrost environment may adversely affect on ec展开更多
基金supported by the National Key Technology R&D Program 2008BAK50B02CAS Innovation Key Program (Grant No. KZCX2-YW-BR-14)+2 种基金National Basic Research Program of China(2011CB309704)Special Scientific Research Project for Public Interest (Grant No. GYHY201006021)the National Natural Science Foundation of China (Grant Nos.40890155, 40775051, U0733002)
文摘The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH： warmer SST in the TIO changes the equivalent potential temperature （EPT） in the atmospheric boundary layer （ABL）, alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.
基金supported by the Natural Science Foundation of Jiangsu Province of China (Grant No. BK2009105)
文摘In this paper, a practical equivalent circuit of an active flux-controlled memristor characterized by smooth piecewise-quadratic nonlinearity is designed and an experimental chaotic memristive circuit is implemented. The chaotic memristive circuit has an equilibrium set and its stability is dependent on the initial state of the memristor. The initial state-dependent and the circuit parameter-dependent dynamics of the chaotic memristive circuit are investigated via phase portraits, bifurcation diagrams and Lyapunov exponents. Both experimental and simulation results validate the proposed equivalent circuit realization of the active flux-controlled memristor.
基金supported by National KeyBasic Research Program of China (Grant No. 2009CB219605)Key Project of National Natural Science Foundation of China (Grant No.40730422)Grand Science and Technology Special Project of China(Grant No. 2011ZX05034-04)
文摘Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well,to diagnose the production state,and to optimize the management of draining and collection of coalbed methane.A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin,based on the results of isothermal adsorption experiments,and an analytical model was developed based on the Langmuir sorption theory.With the model,a numerical method that adopts equivalent desorption rate and its curve was established,which can be used to characterize the staged desorption of coalbed methane.According to the experimental and numerical characterizations,three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage,have been proposed and confirmed,namely,start-up pressure,transition pressure and sensitive pressure.By using these three key pressure points,the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages,i.e.,zero desorption stage,slow desorption stage,transition desorption stage,and sensitive desorption stage.According to analogy analysis,there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production.Moreover,it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage,whereas it is also possible that the declining production stage may occur ahead of schedule.
基金supported by National Natural Science Foundation of China(Grant Nos. 40930530 and 40901180)
文摘Highly accurate observations at various scales on the land surface are urgently needed for the studies of many areas,such as hydrology,meteorology,and agriculture.With the rapid development of remote sensing techniques,remote sensing has had the capacity of monitoring many factors of the Earth's land surface.Especially,the space-borne microwave remote sensing systems have been widely used in the quantitative monitoring of global snow,soil moisture,and vegetation parameters with their all-weather,all-time observation capabilities and their sensitivities to the characteristics of land surface factors.Based on the electromagnetic theories and microwave radiative transfer equations,researchers have achieved great successes in the microwave remote sensing studies for different sensors in recent years.This article has systematically reviewed the progresses on five research areas including microwave theoretical modeling,microwave inversion on soil moisture,snow,vegetation and land surface temperatures.Through the further enrichment of remote sensing datasets and the development of remote sensing theories and inversion techniques,remote sensing including microwave remote sensing will play a more important role in the studies and applications of the Earth systems.
基金supported by the National Natural Science Foundation of China (Grant Nos.50725828,50808041)Scientific Research Foundation of Graduate School of Southeast University (Grant No. YBJJ0923)Teaching and Research Foundation for Excellent Young Teacher of Southeast University
文摘A reliability assessment method of fatigue life based on the long-term monitoring data is developed for welded details in steel box girder,and the application research is presented with examples of welded rib-to-deck details in Runyang Bridges. Firstly the fatigue damage limit-state function is established based on S-N curves and Miner's rule,and the probability distribution characteristics of the coefficients in the function are discussed in detail. The uncertainties in fatigue loading effects are mainly studied based on long-term monitoring data. In the traditional studies,only the uncertainty of equivalent stress range is considered in fatigue reliability assessment. However,stress cycle number is also treated as a random variable in this paper because we know traffic flow every day differs in a thousand ways. Then the optimization method is employed to calculate the fatigue reliability. After studying the changing law of the reliability indices with time and the effect of the randomness of stress cycle number on reliability,the effect of the traffic growth on the reliability is studied. This study shows that the uncertainty in the fatigue life of the welded details can be well studied based on structural health monitoring,so it is necessary to carry out long-term strain monitoring of the welded details for accurate fatigue reliability assessment during the whole service period.
基金supported by the National Basic Research Program of China("973"Program)(Grant No.2006CB202404)
文摘Based on the characteristics of fractured vuggy porous media,a novel mathematical model was proposed to model fluid flow in such media on fine scale,i.e.,the discrete fracture-vug network model.The new model consists of three systems:porous rock system,fracture system,and vug system.The fractures and vugs are embedded in porous rock,and the isolated vugs could be connected via the discrete fracture network.The flow in porous rock and fractures follows Darcy's law,and the vugs system is free fluid region.Using a two-scale homogenization limit theory,we obtained a macroscopic Darcy's law governing the media on coarse scale.The theoretical formula of the equivalent permeability of the fractured vuggy porous media was derived.The model and method of this paper were verified by some numerical examples.At the end the permeability of some fractured vuggy porous media with typical fracture-vug structures was analyzed.
基金funded by SGCC Science and Technology Program under project Research on Electromagnetic Transient Simulation Technology for Large-scale MMC-HVDC Systems.
文摘Multi-terminal direct current(MTDC)grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy.The modular multilevel converter(MMC)has become the basic building block for MTDC and DC grids due to its salient features,i.e.,modularity and scalability.Therefore,the MMC-based MTDC systems should be pervasively embedded into the present power system to improve system performance.However,several technical challenges hamper their practical applications and deployment,including modeling,control,and protection of the MMC-MTDC grids.This paper presents a comprehensive investigation and reference in modeling,control,and protection of the MMC-MTDC grids.A general overview of state-of-the-art modeling techniques of the MMC along with their performance in simulation analysis for MTDC applications is provided.A review of control strategies of the MMC-MTDC grids which provide AC system support is presented.State-of-the art protection techniques of the MMCMTDC systems are also investigated.Finally,the associated research challenges and trends are highlighted.
基金provided by the National Natural Science Foundation of China (Nos. 51074165 and 50834004)
文摘The surface deformation after fully mechanized back filling mining was analyzed.The surface deformation for different backfill materials was predicted by an equivalent mining height model and numerical simulations.The results suggest that:(1) As the elastic modulus,E,of the backfill material increases the surface subsidence decreases.The rate of subsidence decrease drops after E is larger than 5 GPa;(2) Fully mechanized back fill mining technology can effectively control surface deformation.The resulting surface deformation is within the specification grade I,which means surface maintenance is not needed.A site survey showed that the equivalent mining height model is capable of predicting and analyzing surface deformation and that the model is conservative enough for engineering safety.Finally,the significance of establishing a complete error correction system based on error analysis and correction is discussed.
基金National Natural Science Foundation of China,No.41171449,No.41301121,No.41430636The Key Research Program of the Chinese Academy of Sciences,No.KZZD-EW-06-01
文摘Human activity intensity is a synthesis index for describing the effects and influences of human activities on land surface. This paper presents the concept of human activity intensity of land surface and construction land equivalent, builds an algorithm model for human activity intensity, and establishes a method for converting different land use/cover types into construction land equivalent as well. An application in China based on the land use data from 1984 to 2008 is also included. The results show that China＇s human activity intensity rose slowly before 2000, while rapidly after 2000. It experienced an increase from 7.63% in 1984 to 8.54% in 2008. It could be generally divided into five levels： Very High, High, Medium, Low, and Very Low, according to the human activity intensity at county level in 2008, which is rated by above 27%, 16%-27%, 10%-16%, 6%-10%, and below 6%. China＇s human activity intensity was spatially split into eastern and western parts by the line of Helan Mountains-Longmen Mountains-Jinghong. The eastern part was characterized by the levels of Very High, High, and Medium, and the levels of Low and Very Low were zonally distributed in the mountainous and hilly areas. In contrast, the western part was featured by the Low and Very Low levels, and the levels of Medium and High were scattered in Gansu Hexi Corridor, the east of Qinghai, and the northern and southern slopes of Tianshan Mountains in Xinjiang.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11103064 and 11173049)the Shanghai Committee of Science and Technology, China (Grant No. 11ZR1443500)
文摘The regional satellite navigation system of COMPASS (Phase I) provides both open services and authorized services. Authorized services offer differential corrections and integrity information to users to support higher positioning, navigation and timing precision. Experimenting with real data, positioning accuracy is estimated with a 3GEO/4IGSO COMPASS constellation. The results show that with dual-frequency and single-frequency pseudo-range measurements, the positioning errors are respectively 8 and 10 m (RMS) for open service users, while for authorized users, the errors are 4 and 5 m (RMS), respectively. The COMPASS constellation geometry may cause large error to occur in the height component by 7-9 m for dualor single-frequency users, which can be effectively reduced with the differential corrections supplied by the authorized services. Multipath errors are identified and corrected for COMPASS, resulting in 25% positioning accuracy improvement for dual-frequency users and 10% improvement for single-frequency users.
文摘The flow resistance factors of non-submerged rigid vegetation in open channels were analyzed. The formulas of drag coefficient CD and equivalent Manning＇s roughness coefficient na were derived by analyzing the force of the flow of non-submerged rigid vegetation in open channel. The flow characteristics and mechanism of non-submerged rigid vegetation in open channel were studied through flume experiments.
基金supported by National Natural Science Foundation of China (Grant Nos. 40821001 and 40701013)Chinese Academy of Sciences (CAS) Knowledge Innovative Program (Grant No. KZCX2-YW- 311)CAS ‘One Hundred Talented People’ Program
文摘Northeastern China has the second largest expanse of permafrost in China,primarily known as Xing'an-Baikal permafrost.Located on the southeastern edges of the Eurasian cryolithozone,the permafrost is thermally unstable and ecologically sensitive to external changes.The combined impacts of climatic,environmental,and anthropogenic changes cause 3-dimensional degradation of the permafrost.To predict these changes on the southern limit and ground temperature of permafrost in Northeastern China,an equivalent latitude model (ELM) for the mean annual ground surface temperature (MAGSTs) was proposed,and further improved to take into account of the influences of vegetation and snow-cover based on observational data and using the SHAW model.Using the finite element method and assuming a climate warming rate of 0.048°C a-1,the ELM was combined with the unsteady-state heat conduction model to simulate permafrost temperatures at present,and to predict those after 50 and 100 a.The results indicate that at present,sporadic permafrost occurs in the zones with MAGSTs of 1.5°C or colder,and there would still be a significant presence of permafrost in the zones with the present MAGSTs of 0.5°C or colder after 50 a,and in those of-0.5°C or colder after 100 a.Furthermore,the total areal extent of permafrost would decrease from 2.57×105 km2 at present to 1.84×105 km2 after 50 a and to 1.29×105 km2 after 100 a,i.e.,a reduction of 28.4% and 49.8% in the permafrost area,respectively.Also the permafrost would degrade more substantially in the east than in the west.Regional warming and thinning of permafrost would also occur.The area of stable permafrost (mean annual ground temperature,or MAGT≤-1.0°C) would decrease from present 1.07×105 to 8.8×104 km2 after 50 a,and further decrease to 5.6×104 km2 after 100 a.As a result,the unstable permafrost and seasonally frozen ground would expand,and the southern limit of permafrost would shift significantly northwards.The changes in the permafrost environment may adversely affect on ec
