Understanding solar coronal heating has been one of the unresolved problems in solar physics in spite of the many theories that have been developed to explain it. Past observational studies suggested that kinetic Alfv...Understanding solar coronal heating has been one of the unresolved problems in solar physics in spite of the many theories that have been developed to explain it. Past observational studies suggested that kinetic Alfven waves(KAWs) may be responsible for solar coronal heating by accelerating the charged particles in solar plasma. In this paper, we investigated the transient dynamics of KAWs with modified background density due to ponderomotive force and Joule heating. A numerical simulation based on pseudospectral method was applied to study the evolution of KAW magnetic coherent structures and generation of magnetic turbulence. Using different initial conditions in simulations, the dependence of KAW dynamics on the nature of inhomogeneous solar plasma was thoroughly investigated. The saturated magnetic power spectra follow Kolmogorov scaling of k^-5/3 in the inertial range, then followed by steep anisotropic scaling in the dissipation range. The KAW has anisotropy of k||∝ k^0.53⊥, k|| ∝ k^0.50⊥, k||∝ k^0.83⊥ and k||∝ k^0.30⊥ depending on the kind of initial conditions of inhomogeneity. The power spectra of magnetic field fluctuations showing the spectral anisotropy in wavenumber space indicate that the nonlinear interactions may be redistributing the energy anisotropically among higher modes of the wavenumber. Therefore, anisotropic turbulence can be considered as one of the candidates responsible for the particle energization and heating of the solar plasmas.展开更多
The process of ion heating by a monochromatic obliquely propagating low-frequency Alfven wave is investigated. This process can be roughly divided into three stages: at first,the ions are picked up by the Alfven wave ...The process of ion heating by a monochromatic obliquely propagating low-frequency Alfven wave is investigated. This process can be roughly divided into three stages: at first,the ions are picked up by the Alfven wave in several gyro-periods and a bulk velocity in the transverse direction is achieved; then, the ions are scattered in the transverse direction by the wave, which produces phase differences between the ions and leads to ion heating, especially in the perpendicular direction; and finally, the ions are stochastically heated due to the subcyclotron resonance. In this paper, with a test particle method, the efficiency and time scale of the ion stochastic heating by a monochromatic obliquely propagating low-frequency Alfven wave are studied. The results show that with the increase of the amplitude, frequency, and propagation angle of the Alfven wave, the efficiency of the ion stochastic heating increases, while the time scale of the ion stochastic heating decreases. With the increase of the plasma beta β, the ions are stochastically heated with less efficiency, and the time scale increases. We also investigate the heating of heavy ion species(He2+and O5+), which can be heated with a higher efficiency by the oblique Alfven wave.展开更多
Resonant heating of H, O+5, and Mg+9 by parallel propagating ioncyclotron Alfven waves in solar coronal holes at a heliocentric distance is studied using the heating rate derived from the quasilinear theory. It is sho...Resonant heating of H, O+5, and Mg+9 by parallel propagating ioncyclotron Alfven waves in solar coronal holes at a heliocentric distance is studied using the heating rate derived from the quasilinear theory. It is shown that the particle-Alfven-wave interaction is a significant microscopic process. The temperatures of the ions are rapidly increased up to the observed order in only microseconds, which implies that simply inserting the quasilinear heating rate into the fluid/MHD energy equation to calculate the radial dependence of ion temperatures may cause errors as the time scales do not match. Different species ions are heated by Alfven waves with a power law spectrum in approximately a mass order.To heat O+5 over Mg+9 as measured by the Ultraviolet Coronagraph Spectrometer (UVCS) in the solar coronal hole at a region≥ 1.9R⊙, the energy density of Alfven waves with a frequency close to the O+5-cyclotron frequency must be at least double of that at the Mg+9-cyclotron frequency. With an appropriate wave-energy spectrum, the heating of H, O+5 and Mg+9 can be consistent with the UVCS measurements in solar coronal holes at a heliocentric distance.展开更多
Propagation of solitary kinetic Alfven waves(KAWs)is investigated in small but finite/3(particle-to-magnetic pressure ratio)collisionless dense plasma whose constituents are non degenerate wann ions,and relativistic d...Propagation of solitary kinetic Alfven waves(KAWs)is investigated in small but finite/3(particle-to-magnetic pressure ratio)collisionless dense plasma whose constituents are non degenerate wann ions,and relativistic degenerate electrons and positrons.Through the use of reductive perturbation technique,Kortweg-de Vries equation is derived to obtain small amplitude localized wave solution of KAWs.The effects of plasma 0,positron concentration,electron relativistic degeneracy parameter,ion thermal temperature and obliqueness parameter on solitary KAWs are studied.The results of this theoretical investigation are aimed at elucidating characteristics of kinetic Alfven solitary waves in relativistic degenerate e-p-i plasmas found in dense astrophysical objects specifically neutron stars and white dwarfs.展开更多
Stability of the kinetic Alfven wave in a plasma of hydrogen, oxygen and electronsis studied. Each species is modeled by drifting ring distributions in the direction parallel to themagnetic field, while in the perpend...Stability of the kinetic Alfven wave in a plasma of hydrogen, oxygen and electronsis studied. Each species is modeled by drifting ring distributions in the direction parallel to themagnetic field, while in the perpendicular direction the distribution is simulated with a loss conetype distribution obtained through the subtraction of two Maxwellian distributions with differenttemperatures. It is found that for frequencies ω* < ωch with ω* and ωch the Doppler shifted andhydrogen ion gyro-frequencies, respectively, the growth rate of the kinetic Alfven wave increaseswith the increase in propagation angles and density of oxygen ions. On the other hand, forfrequencies ω* < ωcO with ωcO the oxygen ion gyro-frequency the growth rate is independent ofthe oxygen ion density.展开更多
We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 A?and 193 passbands,aiming to provide more insights into their physical nature.The damping and power spectra of the in...We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 A?and 193 passbands,aiming to provide more insights into their physical nature.The damping and power spectra of the intensity disturbances with frequencies from 0.07 m Hz to 10.5 m Hz are investigated.The damping of the intensity disturbances tends to be stronger at lower frequencies,and their damping behavior below 980′′(for comparison,the limb is at 945′′) is different from what happens above.No significant difference is found between the damping of the intensity disturbances in the AIA 171 and that in the AIA193 A?.The indices of the power spectra of the intensity disturbances are found to be slightly smaller in the AIA 171 than in the AIA 193 A?,but the difference is within one standard deviation.An additional enhanced component is present in the power spectra in a period range of 8–40 min at lower heights.The power spectra of a spicule is highly correlated with its associated intensity disturbance,which suggests that the power spectra of the intensity disturbances might be a mixture of spicules and wave activities.We suggest that each intensity disturbance in the polar coronal hole is possibly a series of independent slow magnetoacoustic waves triggered by spicular activities.展开更多
Magnetohydrodynamic(MHD) processes are important for the transfer of energy over large scales in plasmas and so are essential to understanding most forms of dynamical activity in the solar atmosphere. The introduction...Magnetohydrodynamic(MHD) processes are important for the transfer of energy over large scales in plasmas and so are essential to understanding most forms of dynamical activity in the solar atmosphere. The introduction of transverse structuring into models for the corona modifies the behavior of MHD waves through processes such as dispersion and mode coupling. Exploiting our understanding of MHD waves with the diagnostic tool of coronal seismology relies upon the development of sufficiently detailed models to account for all the features in observations. The development of realistic models appropriate for highly structured and dynamical plasmas is often beyond the domain of simple mathematical analysis and so numerical methods are employed. This paper reviews recent numerical results for seismology of the solar corona using MHD.展开更多
Magnetoseismology,a technique of magnetic field diagnostics based on observations of magnetohydrodynamic(MHD)waves,has been widely used to estimate the field strengths of oscillating structures in the solar corona.How...Magnetoseismology,a technique of magnetic field diagnostics based on observations of magnetohydrodynamic(MHD)waves,has been widely used to estimate the field strengths of oscillating structures in the solar corona.However,previously magnetoseismology was mostly applied to occasionally occurring oscillation events,providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure.This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter(CoMP).Using several CoMP observations of the Fe xiii 1074.7 nm and 1079.8 nm spectral lines,we obtained maps of the plasma density and wave phase speed in the corona,which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky.We also examined distributions of the electron density and magnetic field strength,and compared their variations with height in the quiet Sun and active regions.Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.展开更多
文摘Understanding solar coronal heating has been one of the unresolved problems in solar physics in spite of the many theories that have been developed to explain it. Past observational studies suggested that kinetic Alfven waves(KAWs) may be responsible for solar coronal heating by accelerating the charged particles in solar plasma. In this paper, we investigated the transient dynamics of KAWs with modified background density due to ponderomotive force and Joule heating. A numerical simulation based on pseudospectral method was applied to study the evolution of KAW magnetic coherent structures and generation of magnetic turbulence. Using different initial conditions in simulations, the dependence of KAW dynamics on the nature of inhomogeneous solar plasma was thoroughly investigated. The saturated magnetic power spectra follow Kolmogorov scaling of k^-5/3 in the inertial range, then followed by steep anisotropic scaling in the dissipation range. The KAW has anisotropy of k||∝ k^0.53⊥, k|| ∝ k^0.50⊥, k||∝ k^0.83⊥ and k||∝ k^0.30⊥ depending on the kind of initial conditions of inhomogeneity. The power spectra of magnetic field fluctuations showing the spectral anisotropy in wavenumber space indicate that the nonlinear interactions may be redistributing the energy anisotropically among higher modes of the wavenumber. Therefore, anisotropic turbulence can be considered as one of the candidates responsible for the particle energization and heating of the solar plasmas.
基金supported by National Natural Science Foundation of China(Nos.41274144,41174124,40931053,41121003)CAS Key ResearchProgram KZZD-EW-01973 Program of China(No.2012CB825602)
文摘The process of ion heating by a monochromatic obliquely propagating low-frequency Alfven wave is investigated. This process can be roughly divided into three stages: at first,the ions are picked up by the Alfven wave in several gyro-periods and a bulk velocity in the transverse direction is achieved; then, the ions are scattered in the transverse direction by the wave, which produces phase differences between the ions and leads to ion heating, especially in the perpendicular direction; and finally, the ions are stochastically heated due to the subcyclotron resonance. In this paper, with a test particle method, the efficiency and time scale of the ion stochastic heating by a monochromatic obliquely propagating low-frequency Alfven wave are studied. The results show that with the increase of the amplitude, frequency, and propagation angle of the Alfven wave, the efficiency of the ion stochastic heating increases, while the time scale of the ion stochastic heating decreases. With the increase of the plasma beta β, the ions are stochastically heated with less efficiency, and the time scale increases. We also investigate the heating of heavy ion species(He2+and O5+), which can be heated with a higher efficiency by the oblique Alfven wave.
基金Supported by the National Natural Science Foundation of China.
文摘Resonant heating of H, O+5, and Mg+9 by parallel propagating ioncyclotron Alfven waves in solar coronal holes at a heliocentric distance is studied using the heating rate derived from the quasilinear theory. It is shown that the particle-Alfven-wave interaction is a significant microscopic process. The temperatures of the ions are rapidly increased up to the observed order in only microseconds, which implies that simply inserting the quasilinear heating rate into the fluid/MHD energy equation to calculate the radial dependence of ion temperatures may cause errors as the time scales do not match. Different species ions are heated by Alfven waves with a power law spectrum in approximately a mass order.To heat O+5 over Mg+9 as measured by the Ultraviolet Coronagraph Spectrometer (UVCS) in the solar coronal hole at a region≥ 1.9R⊙, the energy density of Alfven waves with a frequency close to the O+5-cyclotron frequency must be at least double of that at the Mg+9-cyclotron frequency. With an appropriate wave-energy spectrum, the heating of H, O+5 and Mg+9 can be consistent with the UVCS measurements in solar coronal holes at a heliocentric distance.
文摘Propagation of solitary kinetic Alfven waves(KAWs)is investigated in small but finite/3(particle-to-magnetic pressure ratio)collisionless dense plasma whose constituents are non degenerate wann ions,and relativistic degenerate electrons and positrons.Through the use of reductive perturbation technique,Kortweg-de Vries equation is derived to obtain small amplitude localized wave solution of KAWs.The effects of plasma 0,positron concentration,electron relativistic degeneracy parameter,ion thermal temperature and obliqueness parameter on solitary KAWs are studied.The results of this theoretical investigation are aimed at elucidating characteristics of kinetic Alfven solitary waves in relativistic degenerate e-p-i plasmas found in dense astrophysical objects specifically neutron stars and white dwarfs.
基金the University Grants Commission under its Special Assistance Programme is gratefully acknowledged
文摘Stability of the kinetic Alfven wave in a plasma of hydrogen, oxygen and electronsis studied. Each species is modeled by drifting ring distributions in the direction parallel to themagnetic field, while in the perpendicular direction the distribution is simulated with a loss conetype distribution obtained through the subtraction of two Maxwellian distributions with differenttemperatures. It is found that for frequencies ω* < ωch with ω* and ωch the Doppler shifted andhydrogen ion gyro-frequencies, respectively, the growth rate of the kinetic Alfven wave increaseswith the increase in propagation angles and density of oxygen ions. On the other hand, forfrequencies ω* < ωcO with ωcO the oxygen ion gyro-frequency the growth rate is independent ofthe oxygen ion density.
基金supported by the China 973 program (2012CB825601)the National Natural Science Foundation of China (Grant Nos.41404135 (Z.H.),41274178 and 41474150 (L.X.& Z.H.),and 41174154,41274176 and 41474149 (B.L.))the Shandong Provincial Natural Science Foundation (ZR2014DQ006 (Z.H.))
文摘We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 A?and 193 passbands,aiming to provide more insights into their physical nature.The damping and power spectra of the intensity disturbances with frequencies from 0.07 m Hz to 10.5 m Hz are investigated.The damping of the intensity disturbances tends to be stronger at lower frequencies,and their damping behavior below 980′′(for comparison,the limb is at 945′′) is different from what happens above.No significant difference is found between the damping of the intensity disturbances in the AIA 171 and that in the AIA193 A?.The indices of the power spectra of the intensity disturbances are found to be slightly smaller in the AIA 171 than in the AIA 193 A?,but the difference is within one standard deviation.An additional enhanced component is present in the power spectra in a period range of 8–40 min at lower heights.The power spectra of a spicule is highly correlated with its associated intensity disturbance,which suggests that the power spectra of the intensity disturbances might be a mixture of spicules and wave activities.We suggest that each intensity disturbance in the polar coronal hole is possibly a series of independent slow magnetoacoustic waves triggered by spicular activities.
基金supported by the European Research Council under the SeismoSun Research Project No. 321141the Marie Curie PIRSES-GA-2011-295272 RadioSun project
文摘Magnetohydrodynamic(MHD) processes are important for the transfer of energy over large scales in plasmas and so are essential to understanding most forms of dynamical activity in the solar atmosphere. The introduction of transverse structuring into models for the corona modifies the behavior of MHD waves through processes such as dispersion and mode coupling. Exploiting our understanding of MHD waves with the diagnostic tool of coronal seismology relies upon the development of sufficiently detailed models to account for all the features in observations. The development of realistic models appropriate for highly structured and dynamical plasmas is often beyond the domain of simple mathematical analysis and so numerical methods are employed. This paper reviews recent numerical results for seismology of the solar corona using MHD.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11825301,11790304(11790300))the Strategic Prior-ity Research Program of CAS(Grant No.XDA17040507)+1 种基金and Grant No.1916321TS00103201This material is based upon work supported by the National Center for Atmospheric Research,which is a major facility spon-sored by the National Science Foundation under Cooperative Agreement(Grant No.1852977)。
文摘Magnetoseismology,a technique of magnetic field diagnostics based on observations of magnetohydrodynamic(MHD)waves,has been widely used to estimate the field strengths of oscillating structures in the solar corona.However,previously magnetoseismology was mostly applied to occasionally occurring oscillation events,providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure.This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter(CoMP).Using several CoMP observations of the Fe xiii 1074.7 nm and 1079.8 nm spectral lines,we obtained maps of the plasma density and wave phase speed in the corona,which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky.We also examined distributions of the electron density and magnetic field strength,and compared their variations with height in the quiet Sun and active regions.Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.
