地球等离子体层是向阳侧中低纬度电离层沿着闭合磁力线向上的自然延伸,其中所出现的一类频率覆盖数十赫兹至数千赫兹的哨声模波动称为等离子体层嘶声.自发现以来,等离子体层嘶声就被广泛认为是沉降损失辐射带高能电子的主要等离子体波...地球等离子体层是向阳侧中低纬度电离层沿着闭合磁力线向上的自然延伸,其中所出现的一类频率覆盖数十赫兹至数千赫兹的哨声模波动称为等离子体层嘶声.自发现以来,等离子体层嘶声就被广泛认为是沉降损失辐射带高能电子的主要等离子体波动之一.但是,等离子体层嘶声的起源一直没有定论.潜在的来源分成两类:一类为等离子体层内部背景等离子体噪声,另一类为等离子体层外部波动.2012年发射升空的Van Allen Probes搭载了完备的磁层粒子、场和波动探测仪器,为这一问题的解决带来了新的机遇.本文综述了近5年来利用Van Allen Probes探索等离子体层嘶声内部源区的研究工作,强调背景等离子体噪声可以通过高能电子线性和非线性不稳定性叠加放大成可观测的嘶声,突出内源的广泛分布特性,即在结构上涵盖等离子体层核心和羽流,在地方时上涵盖向阳和背阳侧等离子体层,在径向距离上涵盖外层和内层等离子体层.展开更多
We construct a realistic model to evaluate the chorus wave-particle interaction in the outer radiation belt L = 4.5. This model incorporates a plasmatrough number density model, a field-aligned density model and a rea...We construct a realistic model to evaluate the chorus wave-particle interaction in the outer radiation belt L = 4.5. This model incorporates a plasmatrough number density model, a field-aligned density model and a realistic wave power and frequency model. We solve the 2D bounce-averaged momentum-pitch-angle Fokker-Planck equation and show that the Whistler-mode chorus can be effective in the acceleration of electrons, and enhance the phase space density for energies of -1 MeV by a factor from 10 to 10^3 in about two days, consistent with the observation. We also demonstrate that ignorance of the electron number density variation along field line and magnetic local time in the previous work yields an overestimate of energetic electron phase space density by a factor 5-10 at large pitch-angle after two days, suggesting that a realistic plasma density model is very important to evaluate the evolution of energetic electrons in the outer radiation belt.展开更多
Following our preceding work, we perform a further study on dynamic evolution of energetic electrons in the outer radiation belt L=4.5 due to a band of whistler-mode chorus frequency distributed over a standard Gaussi...Following our preceding work, we perform a further study on dynamic evolution of energetic electrons in the outer radiation belt L=4.5 due to a band of whistler-mode chorus frequency distributed over a standard Gaussian spectrum. We solve the 2D bounce-averaged Fokker-Planek equation by allowing incorporation of cross diffusion rates. Numerical results show that whistler-mode chorus can be effective in acceleration of electrons at large pitch angles, and enhance the phase space density for energies of about 1 MeV by a factor of 10^2 or above in about one day, consistent with observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm. Moreover, neglecting cross diffusion often leads to overestimates of the phase space density evolution at large pitch angle by a factor of 5-10 after one day, with larger errors at smaller pitch angle, suggesting that cross diffusion also plays an important role in wave-particle interaction.展开更多
The bounce-averaged Fokker-Planck equation is solved to study the relativistic electron phase space density （PSD） evolution in the outer radiation belt due to resonant interactions with plasmaspheric plume electroma...The bounce-averaged Fokker-Planck equation is solved to study the relativistic electron phase space density （PSD） evolution in the outer radiation belt due to resonant interactions with plasmaspheric plume electromagnetic ion cyclotron （EMIC） waves. It is found that the PSDs of relativistic electrons can be depleted by 1-3 orders of magnitude in 5h, supporting the previous finding that resonant interactions with EMIC waves may account for the frequently observed relativistic electron flux dropouts in the outer radiation belt during the main phase of a storm. The significant precipitation loss of ~MeV electrons is primarily induced by the EMIC waves in H＋ and He＋ bands. The rapid remove of highly relativistic electrons （〉5MeV） is mainly driven by the EMIC waves in O＋ band at lower pitch-angles, as well as the EMIC waves in H＋ and He＋ bands at larger pitch-angles. Moreover, a stronger depletion of relativistic electrons is found to occur over a wider pitch angle range when EMIC waves are centering relatively higher in the band.展开更多
We investigate the evolution of the phase space density （PSD） of ring current protons induced by electromagnetic ion cyclotron （EMIC） waves at the location L=3.5, calculate the diffusion coefficients in pitch angl...We investigate the evolution of the phase space density （PSD） of ring current protons induced by electromagnetic ion cyclotron （EMIC） waves at the location L=3.5, calculate the diffusion coefficients in pitch angle and momentum, and solve the standard two-dimensional Fokker-Planck diffusion equation. The pitch angle diffusion coefficient is found to be larger than the momentum diffusion coefficient by a factor of about 103 or above at lower pitch angles. We show that EMIC waves can produce efficient pitch angle scattering of energetic （- 100 keV） protons, yielding a rapid decrement in PSD, typically by a factor of - 10 within a few hours, consistent with observational data. This result further supports previous findings that wave-particle interaction is responsible for the rapid ring current decay.展开更多
We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker-Planck equation which governs wave-particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch...We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker-Planck equation which governs wave-particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch angle diffusion coefficients, and temporal evolution of pitch angle distribution for a band of chorus frequency distributed over a standard Gaussian spectrum particularly in the heart of the Earth＇s radiation belt L = 4.5, where peaks of the electron phase space density are observed. We find that the Whistler-mode chorus can produce significant acceleration of electrons at large pitch angles, and can enhance the phase space density for energies of 0.5 - 1 MeV by a factor of 10 or above after about 24h. This result can account for observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm.展开更多
An extreme ultra-violet（EUV） wave is characterized as a bright pulse that has emanated from the solar eruption source and can propagate globally in the solar corona. According to one leading theory, the EUV wave is ...An extreme ultra-violet（EUV） wave is characterized as a bright pulse that has emanated from the solar eruption source and can propagate globally in the solar corona. According to one leading theory, the EUV wave is a fast magnetoacoustic wave, as the coronal counterpart of the Moreton wave in the chromosphere. However, previous observations have shown that the EUV wave differs significantly from the Moreton wave in both velocity and lifetime. To reconcile these differences, here we analyze the wave characteristics of a two-fluid MHD model in the stratified solar atmosphere with a height-dependent ionization rate. It is found that the collision between neutral and ionized fluids is able to attenuate the wave amplitude, while causing a slight change in its propagation velocity. Because the chromosphere has the lower ionization rate and the stronger magnetic fields than the corona,the velocity of the Moreton wave is much higher than that of the EUV wave. In contrast to the Moreton waves damped strongly by the collision between neutral and ionized fluids, the EUV wave in the fully ionized corona is able to propagate globally on a time scale of several hours. Our results support the previous theory that fast magnetoacoustic waves account for both EUV and Moreteon waves in the different layers of the solar atmosphere.展开更多
文摘地球等离子体层是向阳侧中低纬度电离层沿着闭合磁力线向上的自然延伸,其中所出现的一类频率覆盖数十赫兹至数千赫兹的哨声模波动称为等离子体层嘶声.自发现以来,等离子体层嘶声就被广泛认为是沉降损失辐射带高能电子的主要等离子体波动之一.但是,等离子体层嘶声的起源一直没有定论.潜在的来源分成两类:一类为等离子体层内部背景等离子体噪声,另一类为等离子体层外部波动.2012年发射升空的Van Allen Probes搭载了完备的磁层粒子、场和波动探测仪器,为这一问题的解决带来了新的机遇.本文综述了近5年来利用Van Allen Probes探索等离子体层嘶声内部源区的研究工作,强调背景等离子体噪声可以通过高能电子线性和非线性不稳定性叠加放大成可观测的嘶声,突出内源的广泛分布特性,即在结构上涵盖等离子体层核心和羽流,在地方时上涵盖向阳和背阳侧等离子体层,在径向距离上涵盖外层和内层等离子体层.
基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB 41000000)the National Natural Science Foundation of China(41774170 and 41631071).
基金Supported by the National Natural Science Foundation of China Grant Nos 40774077, 40774078 and 40874076, the National Key Basic Research Special Foundation of China Grant No 2006CB806304, and the Chinese Academy of Sciences under Grant No KZCX3-SW- 144.
文摘We construct a realistic model to evaluate the chorus wave-particle interaction in the outer radiation belt L = 4.5. This model incorporates a plasmatrough number density model, a field-aligned density model and a realistic wave power and frequency model. We solve the 2D bounce-averaged momentum-pitch-angle Fokker-Planck equation and show that the Whistler-mode chorus can be effective in the acceleration of electrons, and enhance the phase space density for energies of -1 MeV by a factor from 10 to 10^3 in about two days, consistent with the observation. We also demonstrate that ignorance of the electron number density variation along field line and magnetic local time in the previous work yields an overestimate of energetic electron phase space density by a factor 5-10 at large pitch-angle after two days, suggesting that a realistic plasma density model is very important to evaluate the evolution of energetic electrons in the outer radiation belt.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40774077, 40774078 and 40774079, and the National Basic Research Programme of China under Crant No 2006CB806304.
文摘Following our preceding work, we perform a further study on dynamic evolution of energetic electrons in the outer radiation belt L=4.5 due to a band of whistler-mode chorus frequency distributed over a standard Gaussian spectrum. We solve the 2D bounce-averaged Fokker-Planek equation by allowing incorporation of cross diffusion rates. Numerical results show that whistler-mode chorus can be effective in acceleration of electrons at large pitch angles, and enhance the phase space density for energies of about 1 MeV by a factor of 10^2 or above in about one day, consistent with observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm. Moreover, neglecting cross diffusion often leads to overestimates of the phase space density evolution at large pitch angle by a factor of 5-10 after one day, with larger errors at smaller pitch angle, suggesting that cross diffusion also plays an important role in wave-particle interaction.
基金Supported by the National Natural Science Foundation of China grants 40774077, 40774078 and 40874076, and the Innovative Fund of University of Science and Technology of China for Graduate Students under Grant No KD2008033.
文摘The bounce-averaged Fokker-Planck equation is solved to study the relativistic electron phase space density （PSD） evolution in the outer radiation belt due to resonant interactions with plasmaspheric plume electromagnetic ion cyclotron （EMIC） waves. It is found that the PSDs of relativistic electrons can be depleted by 1-3 orders of magnitude in 5h, supporting the previous finding that resonant interactions with EMIC waves may account for the frequently observed relativistic electron flux dropouts in the outer radiation belt during the main phase of a storm. The significant precipitation loss of ~MeV electrons is primarily induced by the EMIC waves in H＋ and He＋ bands. The rapid remove of highly relativistic electrons （〉5MeV） is mainly driven by the EMIC waves in O＋ band at lower pitch-angles, as well as the EMIC waves in H＋ and He＋ bands at larger pitch-angles. Moreover, a stronger depletion of relativistic electrons is found to occur over a wider pitch angle range when EMIC waves are centering relatively higher in the band.
基金Supported by the National Natural Science Foundation of China Grant Nos 40874076, 40774079, 40774078 and 40774077, the Special Fund for Public Welfare Industry （meteorology） GYHY200806024, and the Visiting Scholar Foundation of State Key Laboratory for Space Weather, Chinese Academy of Sciences.
文摘We investigate the evolution of the phase space density （PSD） of ring current protons induced by electromagnetic ion cyclotron （EMIC） waves at the location L=3.5, calculate the diffusion coefficients in pitch angle and momentum, and solve the standard two-dimensional Fokker-Planck diffusion equation. The pitch angle diffusion coefficient is found to be larger than the momentum diffusion coefficient by a factor of about 103 or above at lower pitch angles. We show that EMIC waves can produce efficient pitch angle scattering of energetic （- 100 keV） protons, yielding a rapid decrement in PSD, typically by a factor of - 10 within a few hours, consistent with observational data. This result further supports previous findings that wave-particle interaction is responsible for the rapid ring current decay.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40774077, 40774079 and 40774078, the Chinese Academy of Sciences under Grant No KZCX3-SW-144, and the National Key Basic Research Special Foundation of China under Grant No 2006CB806304.
文摘We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker-Planck equation which governs wave-particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch angle diffusion coefficients, and temporal evolution of pitch angle distribution for a band of chorus frequency distributed over a standard Gaussian spectrum particularly in the heart of the Earth＇s radiation belt L = 4.5, where peaks of the electron phase space density are observed. We find that the Whistler-mode chorus can produce significant acceleration of electrons at large pitch angles, and can enhance the phase space density for energies of 0.5 - 1 MeV by a factor of 10 or above after about 24h. This result can account for observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm.
文摘An extreme ultra-violet（EUV） wave is characterized as a bright pulse that has emanated from the solar eruption source and can propagate globally in the solar corona. According to one leading theory, the EUV wave is a fast magnetoacoustic wave, as the coronal counterpart of the Moreton wave in the chromosphere. However, previous observations have shown that the EUV wave differs significantly from the Moreton wave in both velocity and lifetime. To reconcile these differences, here we analyze the wave characteristics of a two-fluid MHD model in the stratified solar atmosphere with a height-dependent ionization rate. It is found that the collision between neutral and ionized fluids is able to attenuate the wave amplitude, while causing a slight change in its propagation velocity. Because the chromosphere has the lower ionization rate and the stronger magnetic fields than the corona,the velocity of the Moreton wave is much higher than that of the EUV wave. In contrast to the Moreton waves damped strongly by the collision between neutral and ionized fluids, the EUV wave in the fully ionized corona is able to propagate globally on a time scale of several hours. Our results support the previous theory that fast magnetoacoustic waves account for both EUV and Moreteon waves in the different layers of the solar atmosphere.
