The toroidal component of the velocity for geodesic acoustic modes(GAMs)is first demonstrated.Multiple Langmuir probe arrays set up near the top tokamak of the J-TEXT were utilized for this study.A significant peak at...The toroidal component of the velocity for geodesic acoustic modes(GAMs)is first demonstrated.Multiple Langmuir probe arrays set up near the top tokamak of the J-TEXT were utilized for this study.A significant peak at the GAM frequency is observed in Mach number fluctuations.The toroidal velocity for the GAMs is estimated as 10–100 ms-1 and increases with the poloidal velocity.The ratio of toroidal component to the poloidal one of the velocity is mainly located in the interval between 0.3 and 1.0.With higher safety factors q,the ratio almost does not change with decreasing the safety factor,whereas it goes up sharply at low q.The coherencies between poloidal electric fields and Mach number fluctuations in turbulence frequency bands are also evaluated,and are higher than those between radial electric fields and Mach number fluctuations.展开更多
There are two distinct phases in the evolution of drift wave envelope in the presence of zonal flow.A long-lived standing wave phase,which we call the Caviton,and a short-lived traveling wave phase(in radial direction...There are two distinct phases in the evolution of drift wave envelope in the presence of zonal flow.A long-lived standing wave phase,which we call the Caviton,and a short-lived traveling wave phase(in radial direction) we call the Instanton.Several abrupt phenomena observed in tokamaks,such as intermittent excitation of geodesic acoustic mode(GAM) shown in this paper,could be attributed to the sudden and fast radial motion of Instanton.The composite drift wave-zonal flow system evolves at the two well-separate scales:the micro-scale and the meso-scale.The eigenmode equation of the model defines the zero-order(micro-scale) variation;it is solved by making use of the two-dimensional(2 D) weakly asymmetric ballooning theory(WABT),a theory suitable for modes localized to rational surface like drift waves,and then refined by shifted inverse power method,an iterative finite difference method.The next order is the equation of electron drift wave(EDW) envelope(containing group velocity of EDW) which is modulated by the zonal flow generated by Reynolds stress of EDW.This equation is coupled to the zonal flow equation,and numerically solved in spatiotemporal representation;the results are displayed in self-explanatory graphs.One observes a strong correlation between the Caviton-Instanton transition and the zero-crossing of radial group velocity of EDW.The calculation brings out the defining characteristics of the Instanton:it begins as a linear traveling wave right after the transition.Then,it evolves to a nonlinear stage with increasing frequency all the way to 20 kHz.The modulation to Reynolds stress in zonal flow equation brought in by the nonlinear Instanton will cause resonant excitation to GAM.The intermittency is shown due to the random phase mixing between multiple central rational surfaces in the reaction region.展开更多
By utilizing the two numerical codes RFPA3 D and FLAC3 D, the effect of heterogeneity on failure mode and failure mechanism of rock around deep underground excavations under tri-axial stress is analyzed. It is found t...By utilizing the two numerical codes RFPA3 D and FLAC3 D, the effect of heterogeneity on failure mode and failure mechanism of rock around deep underground excavations under tri-axial stress is analyzed. It is found that zonal disintegration is a large scale shear-slip failure developed in deep surrounding rock mass under tri-axial stress, which is accompanied by a large amount of tensile failure. The distance between fractures and the number of fractures have a close correlation with the rock mass heterogeneity. With an increase of the homogeneity index of the rock mass, the distances between fractures decrease and the number of fractures increases. For an intact hard rock mass with relative high homogeneity, only failure mode characterized as v-shaped notches can be formed due to the intersection of intensively developed shear bands. None of the zonal disintegration can be formed due to the fact that with increasing homogeneity, the failure mechanism of rock mass is gradually dominated by shear failure rather than tensile failure.展开更多
Through a systematically developed theory,we demonstrate that the motion of Instanton identified in Zhang et al(2017 Phys.Plasmas 24122304)is highly correlated to the intermittent excitation and propagation of geodesi...Through a systematically developed theory,we demonstrate that the motion of Instanton identified in Zhang et al(2017 Phys.Plasmas 24122304)is highly correlated to the intermittent excitation and propagation of geodesic acoustic mode(GAM)that is observed in tokamaks.While many numerical simulations have observed the phenomena,it is the first theory that reveals the physical mechanism behind GAM intermittent excitation and propagation.The preceding work is based on the micro-turbulence associated with toroidal ion temperature gradient mode,and slab-based phenomenological model of zonal flow.When full toroidal effect is introduced into the system,two branches of zonal flow emerge:the torus-modified low frequency zonal flow(TLFZF),and GAM,necessitating a unified exploration of GAM and TLFZF.Indeed,we observe that the transition from the Caviton to Instanton is triggered by a rapid zero-crossing of radial group velocity of drift wave and is found to be strongly correlated with the GAM onset.Many features peculiar to intermittent GAMs,observed in real machines,are thus identified in the numerical experiment.The results will be displayed in figures and in a movie;first for single central rational surface,and then with coupled multiple central rational surfaces.The periodic bursting first shown disappears as being replaced by irregular one,more similar to the intermittent characteristics observed in GAM experiments.展开更多
Zonal mean annual temperature trends were estimated using four reanalysis and three analysis grid datasets. The trends over land and for the entire globe were estimated from 1958-2001 and 1979-2007, respectively. Esti...Zonal mean annual temperature trends were estimated using four reanalysis and three analysis grid datasets. The trends over land and for the entire globe were estimated from 1958-2001 and 1979-2007, respectively. Estimates of temperature trends over land from Climate Research Unit （CRU） analysis data indicate more intense wanning moving northward, at a rate of about 3.5℃ per century at 65°N, then declining further to the north. CRU estimates indicated dramatic warming over the latitudes of the Antarctic Peninsula, with a localized cooling trend at 45°S. A global estimate was conducted by comparing estimates of the reanalysis datasets. Temperature distribution trends of the reanalysis data were similar to those generated by land observations but with large bias in the Polar Regions. The bias could be reduced by comparing these estimates with those from the analysis data at high latitudes. Extreme warming trends were esti- mated at rates of 2.9℃-3.5℃ per century in the Arctic and 3.2℃-4.7℃ per century in the Antarctic for 1958-2001. Surface warming was even more intense in the Northern Hemisphere for 1979-2007, with extreme arctic warming rates ranging from 8.5℃-8.9℃ per century, as estimated by the analysis and reanalysis datasets. Trends over Antarctica for this period were contradictory, as Japan Meteorological Agency （JMA） reanalysis （JRA-25） indicated a cooling trend at about -7℃ per century, while other reanalysis datasets showed sharp warming over the continent.展开更多
Zonal wind stress plays an important role in the evolution of El Ni（n）o-Southern Oscillation （ENSO） events;however,a comprehensive comparison and analysis in terms of model performance and related bias in the inte...Zonal wind stress plays an important role in the evolution of El Ni（n）o-Southern Oscillation （ENSO） events;however,a comprehensive comparison and analysis in terms of model performance and related bias in the interannual variability of zonal wind stress across the tropical Pacific has yet to be performed.In this study,the authors evaluate how well the individual atmospheric models participating in phase 5 of the Coupled Model Intercomparison Project simulate zonal wind stress.It is found that the wind stress anomalies simulated by the multi-model ensemble are weaker than those in the observation in both El Ni（n）o and La Ni（n）a events,with a larger bias in the former.Further analysis indicates that the bias associated with El Ni（n）o events may be mainly attributable to the weaker negative precipitation anomalies in the AMIP simulations,compared with observations,over the eastern Indian Ocean.Through the Gill-like responses in atmospheric circulation,the rainfall bias over the eastern Indian Ocean results in an easterly wind stress anomaly in the western and central equatorial Pacific,which to some extent offsets the westerly wind stress anomalies associated with El Ni（n）o events.Consequently,the responses of zonal wind stress anomalies to warm SST anomalies are much underestimated in AMIP simulations during El Niffo events.展开更多
This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particula...This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particular emphasis on interactive stratosphere-troposphere processes. The submonthly variability is identified and measured using a daily NAM index, which concentrates primarily on zonally symmetrical circulation. A schematic lifecycle of submonthly variability is developed that reveals a two-way coupling pro- cess between the stratosphere and troposphere in the NH polar region. Specifically, anomalous tropospheric zonal winds in the Atlantic and Pacific sectors of the Arctic propagate upwards to the low stratosphere, disturbing the polar vortex, and resulting in an anomalous stratospheric geopotential height （HGT） that subsequently propagates down into the troposphere and changes the sign of the surface circulations. From the standpoint of planetary-scale wave activities, a feedback loop is also evident when the anoma- lous planetary-scale waves （with wavenumbers 2 and 3） propagate upwards, which disturbs the anomalous zonally symmetrical flow in the low stratosphere, and induces the anomalous HGT to move poleward in the low stratosphere, and then propagates down into the troposphere. This increases the energy of waves at wavenumbers 2 and 3 in the low troposphere in middle latitudes by enhancing the land-sea contrast of the anomalous HGT field. Thus, this study supports the viewpoint that the downward propagation of stratospheric NAM signals may not originate in the stratosphere.展开更多
This paper reviews the theoretical foundations of zonal flow, putting emphasis on the linear response function of plasma to the external flow drive. An extension of the theory is made in order to apply it to helical s...This paper reviews the theoretical foundations of zonal flow, putting emphasis on the linear response function of plasma to the external flow drive. An extension of the theory is made in order to apply it to helical systems and to study the properties of the zonal flow in the low frequency range. Further refinement of the theory is made incorporating the orbital effects of particles more precisely, and the role of neoclassical polarization current is identified.展开更多
A linear response function for zonal flows is obtained by solving the gyro-kinetic equation. This is an extension of a previous work which adopted the method of ＂integrating along particle orbit＂ to solve the drift ...A linear response function for zonal flows is obtained by solving the gyro-kinetic equation. This is an extension of a previous work which adopted the method of ＂integrating along particle orbit＂ to solve the drift kinetic equation. The formula derived in this paper is used to calculate the dispersion relation of geodesic acoustic mode, which is then compared with that of the gyro-kinetic analytic formula.展开更多
Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary mo...Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary modes propagating at both electron and ion diamagnetic drift directions in contrast to the assertion in previous studies that only primary modes propagating in the ion diamagnetic drift directions can drive zonal instabilities. Generally, the growth rate of the driven zonal mode is in the same order as that in previous study. However, different from the previous work, the growth rate is no longer proportional to the difference between the diamagnetic drift frequencies of electrons and ions.展开更多
Properties of the geodesic acoustic mode （GAM） density fluctuations are studied using two toroidally separated Langnmir triple-probe arrays on the top of HT-7 tokamak. The GAM scenario is identified in the potential...Properties of the geodesic acoustic mode （GAM） density fluctuations are studied using two toroidally separated Langnmir triple-probe arrays on the top of HT-7 tokamak. The GAM scenario is identified in the potential fluctuations with the toroidally symmetric structure （n =0） and satisfying the temperature scaling of GAM mode frequency. Some theoretical predictions about the mode features of GAM density fluctuations are verified in our experiments： the toroidal mode number of GAM density fluctuations is n = 0; its amplitude is consistent with the theoretical prediction in a factor of 2; the density and potential fluctuations of GAM is in anti-phase at the top of plasma cross-section. Strong nonlinear interactions are found between GAM density fluctuations and ambient turbulence （AT）. The results support the conclusions that the envelope modulation of potential fluctuations is dominantly caused by the direct regulation of GAM in the generation processing, and the envelope modulation of density fluctuation is due to the GAM shear effect.展开更多
基金supported by National Natural Science Foundation of China(Nos.12075057,11775069,11320101005,51821005 and 11875020)Jiangxi Provincial Natural Science Foundation(No.20202ACBL201002)+1 种基金Doctoral Foundation(Nos.DHBK2017134 and DHBK 2018059)Grant-in-Aid for Scientific Research of JSPS(Nos.15H02155,15H02335,16H02442)。
文摘The toroidal component of the velocity for geodesic acoustic modes(GAMs)is first demonstrated.Multiple Langmuir probe arrays set up near the top tokamak of the J-TEXT were utilized for this study.A significant peak at the GAM frequency is observed in Mach number fluctuations.The toroidal velocity for the GAMs is estimated as 10–100 ms-1 and increases with the poloidal velocity.The ratio of toroidal component to the poloidal one of the velocity is mainly located in the interval between 0.3 and 1.0.With higher safety factors q,the ratio almost does not change with decreasing the safety factor,whereas it goes up sharply at low q.The coherencies between poloidal electric fields and Mach number fluctuations in turbulence frequency bands are also evaluated,and are higher than those between radial electric fields and Mach number fluctuations.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1967206,11975231,11805203,and 11775222)the National MCF Energy Research and Development Program,China(Grant Nos.2018YFE0311200 and 2017YFE0301204)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDB-SSW-SYS004)。
文摘There are two distinct phases in the evolution of drift wave envelope in the presence of zonal flow.A long-lived standing wave phase,which we call the Caviton,and a short-lived traveling wave phase(in radial direction) we call the Instanton.Several abrupt phenomena observed in tokamaks,such as intermittent excitation of geodesic acoustic mode(GAM) shown in this paper,could be attributed to the sudden and fast radial motion of Instanton.The composite drift wave-zonal flow system evolves at the two well-separate scales:the micro-scale and the meso-scale.The eigenmode equation of the model defines the zero-order(micro-scale) variation;it is solved by making use of the two-dimensional(2 D) weakly asymmetric ballooning theory(WABT),a theory suitable for modes localized to rational surface like drift waves,and then refined by shifted inverse power method,an iterative finite difference method.The next order is the equation of electron drift wave(EDW) envelope(containing group velocity of EDW) which is modulated by the zonal flow generated by Reynolds stress of EDW.This equation is coupled to the zonal flow equation,and numerically solved in spatiotemporal representation;the results are displayed in self-explanatory graphs.One observes a strong correlation between the Caviton-Instanton transition and the zero-crossing of radial group velocity of EDW.The calculation brings out the defining characteristics of the Instanton:it begins as a linear traveling wave right after the transition.Then,it evolves to a nonlinear stage with increasing frequency all the way to 20 kHz.The modulation to Reynolds stress in zonal flow equation brought in by the nonlinear Instanton will cause resonant excitation to GAM.The intermittency is shown due to the random phase mixing between multiple central rational surfaces in the reaction region.
基金supported by the National Natural Science Foundation of China (Nos. 51304036, 51222401 and 51174045)the Fundamental Research Funds for the Central Universities of China(Nos. N120101001 and N120601002)+1 种基金the National Basic Research Program of China (No. 2013CB227900)the China-South Africa Joint Research Program (No. 2012DFG71060)
文摘By utilizing the two numerical codes RFPA3 D and FLAC3 D, the effect of heterogeneity on failure mode and failure mechanism of rock around deep underground excavations under tri-axial stress is analyzed. It is found that zonal disintegration is a large scale shear-slip failure developed in deep surrounding rock mass under tri-axial stress, which is accompanied by a large amount of tensile failure. The distance between fractures and the number of fractures have a close correlation with the rock mass heterogeneity. With an increase of the homogeneity index of the rock mass, the distances between fractures decrease and the number of fractures increases. For an intact hard rock mass with relative high homogeneity, only failure mode characterized as v-shaped notches can be formed due to the intersection of intensively developed shear bands. None of the zonal disintegration can be formed due to the fact that with increasing homogeneity, the failure mechanism of rock mass is gradually dominated by shear failure rather than tensile failure.
基金supported in part by the National MCF Energy R&D Program of China(Nos.2018YFE0311200 and 2017YFE0301204)National Natural Science Foundation of China(Nos.U1967206,11975231,11805203 and 11775222)+1 种基金Key Research Program of Frontier Science CAS(QYZDB-SSW-SYS004)the US Dept.of Energy(No.DE-FG02-04ER-54742)。
文摘Through a systematically developed theory,we demonstrate that the motion of Instanton identified in Zhang et al(2017 Phys.Plasmas 24122304)is highly correlated to the intermittent excitation and propagation of geodesic acoustic mode(GAM)that is observed in tokamaks.While many numerical simulations have observed the phenomena,it is the first theory that reveals the physical mechanism behind GAM intermittent excitation and propagation.The preceding work is based on the micro-turbulence associated with toroidal ion temperature gradient mode,and slab-based phenomenological model of zonal flow.When full toroidal effect is introduced into the system,two branches of zonal flow emerge:the torus-modified low frequency zonal flow(TLFZF),and GAM,necessitating a unified exploration of GAM and TLFZF.Indeed,we observe that the transition from the Caviton to Instanton is triggered by a rapid zero-crossing of radial group velocity of drift wave and is found to be strongly correlated with the GAM onset.Many features peculiar to intermittent GAMs,observed in real machines,are thus identified in the numerical experiment.The results will be displayed in figures and in a movie;first for single central rational surface,and then with coupled multiple central rational surfaces.The periodic bursting first shown disappears as being replaced by irregular one,more similar to the intermittent characteristics observed in GAM experiments.
基金supported by the National Natural Science Foundation of China (Grant No. 40775048)the National Basic Research Program of China (Grant No. 2006CB400504)Key Projects in the National Science & Technology Pillar Program during the Eleventh Five-Year Plan Period (Grant No. 2007BAC294)
文摘Zonal mean annual temperature trends were estimated using four reanalysis and three analysis grid datasets. The trends over land and for the entire globe were estimated from 1958-2001 and 1979-2007, respectively. Estimates of temperature trends over land from Climate Research Unit （CRU） analysis data indicate more intense wanning moving northward, at a rate of about 3.5℃ per century at 65°N, then declining further to the north. CRU estimates indicated dramatic warming over the latitudes of the Antarctic Peninsula, with a localized cooling trend at 45°S. A global estimate was conducted by comparing estimates of the reanalysis datasets. Temperature distribution trends of the reanalysis data were similar to those generated by land observations but with large bias in the Polar Regions. The bias could be reduced by comparing these estimates with those from the analysis data at high latitudes. Extreme warming trends were esti- mated at rates of 2.9℃-3.5℃ per century in the Arctic and 3.2℃-4.7℃ per century in the Antarctic for 1958-2001. Surface warming was even more intense in the Northern Hemisphere for 1979-2007, with extreme arctic warming rates ranging from 8.5℃-8.9℃ per century, as estimated by the analysis and reanalysis datasets. Trends over Antarctica for this period were contradictory, as Japan Meteorological Agency （JMA） reanalysis （JRA-25） indicated a cooling trend at about -7℃ per century, while other reanalysis datasets showed sharp warming over the continent.
基金supported by the National Natural Science Foundation of China[grant number 41530426]
文摘Zonal wind stress plays an important role in the evolution of El Ni（n）o-Southern Oscillation （ENSO） events;however,a comprehensive comparison and analysis in terms of model performance and related bias in the interannual variability of zonal wind stress across the tropical Pacific has yet to be performed.In this study,the authors evaluate how well the individual atmospheric models participating in phase 5 of the Coupled Model Intercomparison Project simulate zonal wind stress.It is found that the wind stress anomalies simulated by the multi-model ensemble are weaker than those in the observation in both El Ni（n）o and La Ni（n）a events,with a larger bias in the former.Further analysis indicates that the bias associated with El Ni（n）o events may be mainly attributable to the weaker negative precipitation anomalies in the AMIP simulations,compared with observations,over the eastern Indian Ocean.Through the Gill-like responses in atmospheric circulation,the rainfall bias over the eastern Indian Ocean results in an easterly wind stress anomaly in the western and central equatorial Pacific,which to some extent offsets the westerly wind stress anomalies associated with El Ni（n）o events.Consequently,the responses of zonal wind stress anomalies to warm SST anomalies are much underestimated in AMIP simulations during El Niffo events.
基金jointly supported by the R&D Special Fund for Public Welfare Industry(meteorology)of China(Grant No.GYHY201306031)the National Natural Science Foundation of China(Grant No.40905040)the National Science Foundation of United States(Grant No.1107509)
文摘This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particular emphasis on interactive stratosphere-troposphere processes. The submonthly variability is identified and measured using a daily NAM index, which concentrates primarily on zonally symmetrical circulation. A schematic lifecycle of submonthly variability is developed that reveals a two-way coupling pro- cess between the stratosphere and troposphere in the NH polar region. Specifically, anomalous tropospheric zonal winds in the Atlantic and Pacific sectors of the Arctic propagate upwards to the low stratosphere, disturbing the polar vortex, and resulting in an anomalous stratospheric geopotential height （HGT） that subsequently propagates down into the troposphere and changes the sign of the surface circulations. From the standpoint of planetary-scale wave activities, a feedback loop is also evident when the anoma- lous planetary-scale waves （with wavenumbers 2 and 3） propagate upwards, which disturbs the anomalous zonally symmetrical flow in the low stratosphere, and induces the anomalous HGT to move poleward in the low stratosphere, and then propagates down into the troposphere. This increases the energy of waves at wavenumbers 2 and 3 in the low troposphere in middle latitudes by enhancing the land-sea contrast of the anomalous HGT field. Thus, this study supports the viewpoint that the downward propagation of stratospheric NAM signals may not originate in the stratosphere.
基金supported in part by the JSPS-CAS Core University Program in the field of plasma and nuclear fusion
文摘This paper reviews the theoretical foundations of zonal flow, putting emphasis on the linear response function of plasma to the external flow drive. An extension of the theory is made in order to apply it to helical systems and to study the properties of the zonal flow in the low frequency range. Further refinement of the theory is made incorporating the orbital effects of particles more precisely, and the role of neoclassical polarization current is identified.
基金partially supported by the JSPS-CAS Core-University program in the field of 'Plasma and Nuclear Fusion'
文摘A linear response function for zonal flows is obtained by solving the gyro-kinetic equation. This is an extension of a previous work which adopted the method of ＂integrating along particle orbit＂ to solve the drift kinetic equation. The formula derived in this paper is used to calculate the dispersion relation of geodesic acoustic mode, which is then compared with that of the gyro-kinetic analytic formula.
基金supported by National Natural Science Foundation of China (No. 10775137)by the Ministry of Science and Technology of China (No. 2009CB105001)partly by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary modes propagating at both electron and ion diamagnetic drift directions in contrast to the assertion in previous studies that only primary modes propagating in the ion diamagnetic drift directions can drive zonal instabilities. Generally, the growth rate of the driven zonal mode is in the same order as that in previous study. However, different from the previous work, the growth rate is no longer proportional to the difference between the diamagnetic drift frequencies of electrons and ions.
基金supported by National Natural Science Foundation of China (Nos. 10725523, 10875124, 10905057 and 10990212)National Basic Research Program of China (No.2008CB717800)+2 种基金Research Fund for the Doctoral Program of Higher Education of China (No.20060358059)China Postdoctoral Science Foundation (No.20080440104)Knowledge Innovation Program of the Chinese Academy of Sciences (No.kjcx-yw-n28)
文摘Properties of the geodesic acoustic mode （GAM） density fluctuations are studied using two toroidally separated Langnmir triple-probe arrays on the top of HT-7 tokamak. The GAM scenario is identified in the potential fluctuations with the toroidally symmetric structure （n =0） and satisfying the temperature scaling of GAM mode frequency. Some theoretical predictions about the mode features of GAM density fluctuations are verified in our experiments： the toroidal mode number of GAM density fluctuations is n = 0; its amplitude is consistent with the theoretical prediction in a factor of 2; the density and potential fluctuations of GAM is in anti-phase at the top of plasma cross-section. Strong nonlinear interactions are found between GAM density fluctuations and ambient turbulence （AT）. The results support the conclusions that the envelope modulation of potential fluctuations is dominantly caused by the direct regulation of GAM in the generation processing, and the envelope modulation of density fluctuation is due to the GAM shear effect.
