This study explores the model performance of the Coupled Model Intercomparison Project Phase 6(CMIP6)in simulating precipitation extremes over the mid–high latitudes of Asia,as compared with predecessor models in the...This study explores the model performance of the Coupled Model Intercomparison Project Phase 6(CMIP6)in simulating precipitation extremes over the mid–high latitudes of Asia,as compared with predecessor models in the previous phase,CMIP5.Results show that the multimodel ensemble median generally outperforms the individual models in simulating the climate means of precipitation extremes.The CMIP6 models possess a relatively higher capability in this respect than the CMIP5 models.However,discrepancies also exist between models and observation,insofar as most of the simulated indices are positively biased to varying degrees.With respect to the temporal performance of indices,the majority are overestimated at most time points,along with large uncertainty.Therefore,the capacity to simulate the interannual variability needs to be further improved.Furthermore,pairwise and multimodel ensemble comparisons were performed for 12 models to evaluate the performance of individual models,revealing that most of the new-version models are better than their predecessors,albeit with some variance in the metrics amongst models and indices.展开更多
The atmospheric circulation over the mid-high latitudes in Asia has an important influence on regional climate,yet its long-term variation has not been fully explored.The main task of this study is to reveal the inter...The atmospheric circulation over the mid-high latitudes in Asia has an important influence on regional climate,yet its long-term variation has not been fully explored.The main task of this study is to reveal the interdecadal variation features of summer atmospheric circulation over Asian mid-high latitudes in recent decades.The results show that the atmospheric circulation over mid-high latitudes of Asia has stronger interdecadal fluctuations than that over low latitudes and one significant change center appears near Lake Baikal.It is found that the atmospheric circulation near Lake Baikal has a significant interdecadal change around 1996 and a deep anomalous anticyclonic circulation has been controlling this region since then,which contributes to the significant increase in the surface temperature near Lake Baikal since 1997 and makes the region a remarkable warming center in Asia in recent 40 years.During 1997-2015,the pattern of less precipitation in the north and more precipitation in the south of east China is closely related to the anomalous anticyclonic circulation near Lake Baikal.Especially,this anomalous circulation near Lake Baikal has been found to contribute to the obvious interdecadal decrease of the precipitation in northeast China and north China near1997.The sea surface temperature(SST)of northwestern Atlantic is an important influence factor to the interdecadal change in the atmospheric circulation near Lake Baikal around 1996.展开更多
Achieving synergistic absorption of electromagnetic waves(EMWs)in the mid-high frequency and absorption band conversion is an urgent problem.However,the present solution is usually a straightforward mixture of magneti...Achieving synergistic absorption of electromagnetic waves(EMWs)in the mid-high frequency and absorption band conversion is an urgent problem.However,the present solution is usually a straightforward mixture of magnetic component-carbon component.Hereby,we optimize the magnetic properties and electrical relaxation response from a chemical synthesis perspective.Through integrated design,the contents of carbon components and multi-dimensional morphology are controlled by retaining strong magnetic properties.The morphology design and the construction of heterogeneous interfaces will boost the intense response of charge in the surrounding to enhance the polarization effect.The multi-dimensional structure and electromagnetic(EM)properties of the sample after optimized engineering have an extremely powerful absorption conversion effect on EMW energy.NiCo@C particles ultimately achieve synergistic absorption effects at low thickness(d<3.5 mm)at middle frequencies(6–10 GHz)and high frequencies(10.5–18 GHz).Our work establishes a correlation mechanism between the physical and chemical properties of materials and EM parameters.It also provides insight into the synergistic absorption of EMWs in the mid-high frequency and absorption band conversion strategies.展开更多
NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the ...NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the intraseasonal oscillation （ISO; 30-60 days） in the mid-high latitude meridional circulation of the upper troposphere over East Asia. The abrupt transition from drought to flood occurs in early June. The first two recovered fields of the complex empirical orthogonal function show that northward-propagating westerlies from low latitudes converge with southward-propagating westerlies from high latitudes over the mid-low reaches of the Yangtze River （MLRYR） in mid late May. The timing of this convergence corresponds to the flood period in early-mid June. The ISO index is significantly and positively correlated with rainfall over the MLRYR. During the dry phase （before the transition）, the upper troposphere over the MLRYR is characterized by cyclonic flow, easterly winds, and convergence. The regional circulation is dominated by a wave train with a cyclone over east of Lake Baikal, an anticyclone over northern China, and a cyclone over the MLRYR. During the wet phase, the situation is reversed. The configuration of the wave train during the dry phase favors the southward propagation of westerly wind disturbances, while the configuration of the wave train during the wet phase favors the development and maintenance of a pumping effect and sustained ascending motions over the MLRYR.展开更多
Using 32-yr National Centers for Environment Prediction-National Center for Atmospheric Research(NCEP-NCAR) reanalysis data,we investigated zonal propagation and circulation characteristics of the low-frequency circul...Using 32-yr National Centers for Environment Prediction-National Center for Atmospheric Research(NCEP-NCAR) reanalysis data,we investigated zonal propagation and circulation characteristics of the low-frequency circulation for the prevailing period over Eurasian mid-high latitude in boreal summer(May-August) in terms of empirical orthogonal function(EOF),linear regression,and phase analysis and so on.We found that the dominant periods of the low-frequency circulation are 10-30 days and it clearly shows meridional(southward) and zonal(westward) propagation features at the middle troposphere(500 hPa).The average zonal speed of the 10-30 days low-frequency oscillation(LFO) is about 9-10 longitudes per day.Further analysis shows that the southernmost part of the polar vortex in the northern hemisphere exhibits westward clockwise rotation in the eastern hemisphere in boreal summer.Also,the southernmost tips of 5400 and 5500 gpm contours,which indicate the site of the major trough in the eastern hemisphere,obviously move westwards.The southernmost tip of 5500 gpm contour line propagates westwards at the speed of about 9-10 longitudes per day,which is consistent with the mean zonal speed of the westward propagation of the low-frequency circulation.Moreover,the 10-30-day LFO-related cold air also shows west propagation feature with respect to LFO phases.The westward propagation of the LFO is the low-frequency-scale embodiment of the clockwise rotation of polar vortex.The cold air activities closely related to polar vortex or to ridge-trough system activities is the essential circulation of 10-30 days LFO circulation over the Eurasian mid-high latitude in boreal summer.展开更多
亚洲中高纬度地区是受全球变暖影响最严重的地区之一,其生态系统对气候变化高度敏感,该地区植被的未来变化存在很大不确定性。本研究使用第3版全球陆表卫星遥感数据集(Global Land Surface Satellite Product Version 3,GLOBMAP)、第3...亚洲中高纬度地区是受全球变暖影响最严重的地区之一,其生态系统对气候变化高度敏感,该地区植被的未来变化存在很大不确定性。本研究使用第3版全球陆表卫星遥感数据集(Global Land Surface Satellite Product Version 3,GLOBMAP)、第3代全球植被指数数据集(Global Inventory Modeling and Mapping Studies 3rd generation,GIMMS 3g)、全球陆表参数产品(Global Land Surface Satellite Products,GLASS)3套独立的遥感数据集中的叶面积指数(leaf area index,LAI)变量与耦合模式比较计划第5阶段(Coupled Model Intercomparison Project Phase 5,CMIP5)的15个模型、第6阶段(Coupled Model Intercomparison Project Phase 6,CMIP6)的19个模型模拟的叶面积指数及气候因子数据,基于多模型集合均值的方法对亚洲中高纬地区植被的历史及未来特征进行了系统评估。研究结果表明,CMIP6较CMIP5在模拟叶面积指数及其关键气候影响因子(包括地表气温、降水量和地表下行短波辐射)时的不确定性均有所降低。预计在中等排放情景(RCP4.5和SSP2-4.5)和高排放情景(RCP8.5和SSP5-8.5)下亚洲高纬度地区未来的LAI都将增加,且高排放情景下的增长率比中等排放情景更快。未来LAI的增加在暖季比冷季更为显著,表明植被的季节性周期和振幅都将得到增强。在LAI的高值区域,其年度均值与年际标准差增幅相较于LAI的低值区域将更加明显。展开更多
The experience of consumers for products has great effect on the pre-sale strategy. Based on this, the paper studies the selection and pricing of multi-channel marketing models consisting of a brewer, an electronic re...The experience of consumers for products has great effect on the pre-sale strategy. Based on this, the paper studies the selection and pricing of multi-channel marketing models consisting of a brewer, an electronic retailer and a traditional retailer, constructing the non-cooperative game model of brewers and retailers with equal status in four contexts. Finally, the result shows that the introduction of direct channel is bene?cial to increase the brewer's revenue. When the pre-sale marginal revenue is greater than two times the average spot-sale marginal revenue, the total pro?t of supply chain will achieve the best under mode Ⅰ. i.e. both the brewer and e-retailer adopt pre-sale strategy.展开更多
基于模块化多电平换流器的柔性直流输电(modular multilevel convertor based high voltage direct current,MMC-HVDC)系统存在的中高频振荡问题严重危胁电力系统的正常运行。首先,基于MMC的动态相量模型,建立了MMC的交流侧阻抗模型;其...基于模块化多电平换流器的柔性直流输电(modular multilevel convertor based high voltage direct current,MMC-HVDC)系统存在的中高频振荡问题严重危胁电力系统的正常运行。首先,基于MMC的动态相量模型,建立了MMC的交流侧阻抗模型;其次,利用阻抗法分析控制环节及控制参数对MMC阻抗特性的影响,得到了功率外环、电流内环及控制链路延时是导致MMC呈现负阻尼特性的主要原因;再次,在分析现有基于电压前馈环节和电流内环的协同振荡抑制策略不足的基础上,提出了功率外环附加直流电流反馈的振荡抑制策略,极大程度消除系统中的谐波分量,改善了MMC的阻抗特性;最后,通过电磁仿真软件验证理论分析和抑制措施的正确性与有效性。展开更多
基金jointly supported by the National Natural Science Foundation of China grant numbers 41991284 and41922034the Strategic Priority Research Program of the Chinese Academy of Sciences grant number XDA23090102the National Key Research and Development Program of China grant number 2016YFA0602401。
文摘This study explores the model performance of the Coupled Model Intercomparison Project Phase 6(CMIP6)in simulating precipitation extremes over the mid–high latitudes of Asia,as compared with predecessor models in the previous phase,CMIP5.Results show that the multimodel ensemble median generally outperforms the individual models in simulating the climate means of precipitation extremes.The CMIP6 models possess a relatively higher capability in this respect than the CMIP5 models.However,discrepancies also exist between models and observation,insofar as most of the simulated indices are positively biased to varying degrees.With respect to the temporal performance of indices,the majority are overestimated at most time points,along with large uncertainty.Therefore,the capacity to simulate the interannual variability needs to be further improved.Furthermore,pairwise and multimodel ensemble comparisons were performed for 12 models to evaluate the performance of individual models,revealing that most of the new-version models are better than their predecessors,albeit with some variance in the metrics amongst models and indices.
基金Innovation Team Project by Institute of Plateau Meteorology,China Meteorological Administration,Chengdu(BROP202043)National Natural Science Foundation of China(41775084)Key Special Projects of National Key R&D Program of China(2018YFC1505706)。
文摘The atmospheric circulation over the mid-high latitudes in Asia has an important influence on regional climate,yet its long-term variation has not been fully explored.The main task of this study is to reveal the interdecadal variation features of summer atmospheric circulation over Asian mid-high latitudes in recent decades.The results show that the atmospheric circulation over mid-high latitudes of Asia has stronger interdecadal fluctuations than that over low latitudes and one significant change center appears near Lake Baikal.It is found that the atmospheric circulation near Lake Baikal has a significant interdecadal change around 1996 and a deep anomalous anticyclonic circulation has been controlling this region since then,which contributes to the significant increase in the surface temperature near Lake Baikal since 1997 and makes the region a remarkable warming center in Asia in recent 40 years.During 1997-2015,the pattern of less precipitation in the north and more precipitation in the south of east China is closely related to the anomalous anticyclonic circulation near Lake Baikal.Especially,this anomalous circulation near Lake Baikal has been found to contribute to the obvious interdecadal decrease of the precipitation in northeast China and north China near1997.The sea surface temperature(SST)of northwestern Atlantic is an important influence factor to the interdecadal change in the atmospheric circulation near Lake Baikal around 1996.
基金supported by the National Key R&D Program of China(No.2021YFB3502500)and the National Natural Science Foundation of China(Nos.52172091 and 52172295)Open Fund of Key Laboratory of Materials Preparation and Protection for Harsh Environment(Nanjing University of Aeronautics and Astronautics)Ministry of Industry and Information Technology(No.56XCA22042)。
文摘Achieving synergistic absorption of electromagnetic waves(EMWs)in the mid-high frequency and absorption band conversion is an urgent problem.However,the present solution is usually a straightforward mixture of magnetic component-carbon component.Hereby,we optimize the magnetic properties and electrical relaxation response from a chemical synthesis perspective.Through integrated design,the contents of carbon components and multi-dimensional morphology are controlled by retaining strong magnetic properties.The morphology design and the construction of heterogeneous interfaces will boost the intense response of charge in the surrounding to enhance the polarization effect.The multi-dimensional structure and electromagnetic(EM)properties of the sample after optimized engineering have an extremely powerful absorption conversion effect on EMW energy.NiCo@C particles ultimately achieve synergistic absorption effects at low thickness(d<3.5 mm)at middle frequencies(6–10 GHz)and high frequencies(10.5–18 GHz).Our work establishes a correlation mechanism between the physical and chemical properties of materials and EM parameters.It also provides insight into the synergistic absorption of EMWs in the mid-high frequency and absorption band conversion strategies.
基金Supported by the National Natural Science Foundation of China (41221064 and 40875052)China Meteorological Administration Special Public Welfare Research Fund (GYHY200906017 and GYHY201006020)Basic Research Fund of the Chinese Academy of Meteorological Sciences (2010Z003)
文摘NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the intraseasonal oscillation （ISO; 30-60 days） in the mid-high latitude meridional circulation of the upper troposphere over East Asia. The abrupt transition from drought to flood occurs in early June. The first two recovered fields of the complex empirical orthogonal function show that northward-propagating westerlies from low latitudes converge with southward-propagating westerlies from high latitudes over the mid-low reaches of the Yangtze River （MLRYR） in mid late May. The timing of this convergence corresponds to the flood period in early-mid June. The ISO index is significantly and positively correlated with rainfall over the MLRYR. During the dry phase （before the transition）, the upper troposphere over the MLRYR is characterized by cyclonic flow, easterly winds, and convergence. The regional circulation is dominated by a wave train with a cyclone over east of Lake Baikal, an anticyclone over northern China, and a cyclone over the MLRYR. During the wet phase, the situation is reversed. The configuration of the wave train during the dry phase favors the southward propagation of westerly wind disturbances, while the configuration of the wave train during the wet phase favors the development and maintenance of a pumping effect and sustained ascending motions over the MLRYR.
基金supported jointly by the National Natural Science Foundation of China(Grant Nos.40875052&41221064)the Calling Project of China(Grant Nos.GYHY200906017&GYHY201006020)the Basic Research Foundation of CAMS(Grant No.2010Z003)
文摘Using 32-yr National Centers for Environment Prediction-National Center for Atmospheric Research(NCEP-NCAR) reanalysis data,we investigated zonal propagation and circulation characteristics of the low-frequency circulation for the prevailing period over Eurasian mid-high latitude in boreal summer(May-August) in terms of empirical orthogonal function(EOF),linear regression,and phase analysis and so on.We found that the dominant periods of the low-frequency circulation are 10-30 days and it clearly shows meridional(southward) and zonal(westward) propagation features at the middle troposphere(500 hPa).The average zonal speed of the 10-30 days low-frequency oscillation(LFO) is about 9-10 longitudes per day.Further analysis shows that the southernmost part of the polar vortex in the northern hemisphere exhibits westward clockwise rotation in the eastern hemisphere in boreal summer.Also,the southernmost tips of 5400 and 5500 gpm contours,which indicate the site of the major trough in the eastern hemisphere,obviously move westwards.The southernmost tip of 5500 gpm contour line propagates westwards at the speed of about 9-10 longitudes per day,which is consistent with the mean zonal speed of the westward propagation of the low-frequency circulation.Moreover,the 10-30-day LFO-related cold air also shows west propagation feature with respect to LFO phases.The westward propagation of the LFO is the low-frequency-scale embodiment of the clockwise rotation of polar vortex.The cold air activities closely related to polar vortex or to ridge-trough system activities is the essential circulation of 10-30 days LFO circulation over the Eurasian mid-high latitude in boreal summer.
文摘亚洲中高纬度地区是受全球变暖影响最严重的地区之一,其生态系统对气候变化高度敏感,该地区植被的未来变化存在很大不确定性。本研究使用第3版全球陆表卫星遥感数据集(Global Land Surface Satellite Product Version 3,GLOBMAP)、第3代全球植被指数数据集(Global Inventory Modeling and Mapping Studies 3rd generation,GIMMS 3g)、全球陆表参数产品(Global Land Surface Satellite Products,GLASS)3套独立的遥感数据集中的叶面积指数(leaf area index,LAI)变量与耦合模式比较计划第5阶段(Coupled Model Intercomparison Project Phase 5,CMIP5)的15个模型、第6阶段(Coupled Model Intercomparison Project Phase 6,CMIP6)的19个模型模拟的叶面积指数及气候因子数据,基于多模型集合均值的方法对亚洲中高纬地区植被的历史及未来特征进行了系统评估。研究结果表明,CMIP6较CMIP5在模拟叶面积指数及其关键气候影响因子(包括地表气温、降水量和地表下行短波辐射)时的不确定性均有所降低。预计在中等排放情景(RCP4.5和SSP2-4.5)和高排放情景(RCP8.5和SSP5-8.5)下亚洲高纬度地区未来的LAI都将增加,且高排放情景下的增长率比中等排放情景更快。未来LAI的增加在暖季比冷季更为显著,表明植被的季节性周期和振幅都将得到增强。在LAI的高值区域,其年度均值与年际标准差增幅相较于LAI的低值区域将更加明显。
基金Supported by the National Natural Science Foundation of China(71471123)the Fundamental Research Funds for the Central Universities(skqy201621)the Fundamental Research Funds for Soft Science and Technology Project in Sichuan province(2017ZR0030)
文摘The experience of consumers for products has great effect on the pre-sale strategy. Based on this, the paper studies the selection and pricing of multi-channel marketing models consisting of a brewer, an electronic retailer and a traditional retailer, constructing the non-cooperative game model of brewers and retailers with equal status in four contexts. Finally, the result shows that the introduction of direct channel is bene?cial to increase the brewer's revenue. When the pre-sale marginal revenue is greater than two times the average spot-sale marginal revenue, the total pro?t of supply chain will achieve the best under mode Ⅰ. i.e. both the brewer and e-retailer adopt pre-sale strategy.
文摘基于模块化多电平换流器的柔性直流输电(modular multilevel convertor based high voltage direct current,MMC-HVDC)系统存在的中高频振荡问题严重危胁电力系统的正常运行。首先,基于MMC的动态相量模型,建立了MMC的交流侧阻抗模型;其次,利用阻抗法分析控制环节及控制参数对MMC阻抗特性的影响,得到了功率外环、电流内环及控制链路延时是导致MMC呈现负阻尼特性的主要原因;再次,在分析现有基于电压前馈环节和电流内环的协同振荡抑制策略不足的基础上,提出了功率外环附加直流电流反馈的振荡抑制策略,极大程度消除系统中的谐波分量,改善了MMC的阻抗特性;最后,通过电磁仿真软件验证理论分析和抑制措施的正确性与有效性。
