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Ming Zhang - One of the best experts on this subject based on the ideXlab platform.
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Stochastic Propagation of Solar Energetic Particles in Coronal and Interplanetary Magnetic Fields
Journal of Physics: Conference Series, 2019Co-Authors: Ming Zhang, Lulu Zhao, H K RassoulAbstract:This paper describes a method of simulating solar energetic particle propagation through the Magnetic Fields of the solar corona and Interplanetary medium. The simulation code is based on the focus transport equation of energetic particles in 3-d Magnetic Fields, which contains all the particle transport mechanisms, including streaming, convection, gradient/curvature drift, adiabatic focusing, pitch angle scattering by Alfvenic Magnetic field fluctuations and perpendicular diffusion due to the random walk of field lines. In the simulation, particles are injected at their source in the corona, and their guiding center trajectories are calculated using stochastic differential equations. Because of the vastly different time scales of particle transport mechanisms included in the equation, we use the 4-th order Runge-Kutta method to integrate the particle streaming and adiabatic focusing terms, while the stochastic terms of pitch angle scattering and perpendicular diffusion are integrated with the Euler scheme. The model is applied to the 2017 September 10 solar energetic particle event. With perpendicular diffusion, we are able to explain SEP observations from Earth and STEREO-A. A pattern of SEP precipitation on the solar surface is also predicted.
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propagation of solar energetic particles in three dimensional Interplanetary Magnetic Fields in view of characteristics of sources
The Astrophysical Journal, 2011Co-Authors: H Q He, Ming ZhangAbstract:In this paper, a model of solar energetic particle (SEP) propagation in the three-dimensional Parker Interplanetary Magnetic field is calculated numerically. We study the effects of the different aspects of particle sources on the solar surface, which include the source location, coverage of latitude and longitude, and spatial distribution of source particle intensity, on propagation of SEPs with both parallel and perpendicular diffusion. We compute the particle flux and anisotropy profiles at different observation locations in the heliosphere. From our calculations, we find that the observation location relative to the latitudinal and longitudinal coverage of particle source has the strongest effects on particle flux and anisotropy profiles observed by a spacecraft. When a spacecraft is directly connected to the solar sources by the Interplanetary Magnetic field lines, the observed particle fluxes are larger than when the spacecraft is not directly connected. This paper focuses on the situations when a spacecraft is not connected to the particle sources on the solar surface. We find that when the Magnetic footpoint of the spacecraft is farther away from the source, the observed particle flux is smaller and its onset and maximum intensity occur later. When the particle source covers a larger range of latitude and longitude, the observed particle flux is larger and appears earlier. There is east-west azimuthal asymmetry in SEP profiles even when the source distribution is east-west symmetric. However, the detail of particle spatial distribution inside the source does not affect the profile of the SEP flux very much. When the Magnetic footpoint of the spacecraft is significantly far away from the particle source, the anisotropy of particles in the early stage of an SEP event points toward the Sun, which indicates that the first arriving particles come from outside of the observer through perpendicular diffusion at large radial distances.
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propagation of solar energetic particles in three dimensional Interplanetary Magnetic Fields
The Astrophysical Journal, 2009Co-Authors: Ming Zhang, H K RassoulAbstract:This paper presents a model calculation of solar energetic particle propagation in a three-dimensional Interplanetary Magnetic field. The model includes essentially all the particle transport mechanisms: streaming along Magnetic field lines, convection with the solar wind, pitch-angle diffusion, focusing by the inhomogeneous Interplanetary Magnetic field, perpendicular diffusion, and pitch-angle dependent adiabatic cooling by the expanding solar wind. We solve the Fokker–Planck transport equation with simulation of backward stochastic processes in a fixed reference frame in which any spacecraft is roughly stationary. As an example we model the propagation of those high-energy (E 10 MeV) solar energetic particles in gradual events that are accelerated by large coronal mass ejection shocks in the corona and released near the Sun into Interplanetary space of a Parker spiral Magnetic field. Modeled with different scenarios, the source of solar energetic particles can have a full or various limited coverages of latitude and longitude on the solar surface. We compute the long-term time profiles of particle flux and anisotropy at various locations in the heliosphere up to 3 AU, from the ecliptic to high latitudes. Features from particle perpendicular diffusion are revealed. Our simulation reproduces the observed reservoir phenomenon of solar energetic particles with constraints on either solar particle source or the magnitude of perpendicular diffusion.
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ulysses cospin observations of cosmic rays and solar energetic particles from the south pole to the north pole of the sun during solar maximum
Annales Geophysicae, 2003Co-Authors: R B Mckibben, Silvia Dalla, J J Connell, J D Anglin, R G Marsden, C Lopate, T R Sanderson, A. Balogh, Ming Zhang, M Y HoferAbstract:Abstract. In 2000–2001 Ulysses passed from the south to the north polar regions of the Sun in the inner heliosphere, providing a snapshot of the latitudinal structure of cosmic ray modulation and solar energetic particle populations during a period near solar maximum. Observations from the COSPIN suite of energetic charged particle telescopes show that latitude variations in the cosmic ray intensity in the inner heliosphere are nearly non-existent near solar maximum, whereas small but clear latitude gradients were observed during the similar phase of Ulysses’ orbit near the 1994–95 solar minimum. At proton energies above ~10 MeV and extending up to >70 MeV, the intensities are often dominated by Solar Energetic Particles (SEPs) accelerated near the Sun in association with intense solar flares and large Coronal Mass Ejections (CMEs). At lower energies the particle intensities are almost constantly enhanced above background, most likely as a result of a mix of SEPs and particles accelerated by Interplanetary shocks. Simultaneous high-latitude Ulysses and near-Earth observations show that most events that produce large flux increases near Earth also produce flux increases at Ulysses, even at the highest latitudes attained. Particle anisotropies during particle onsets at Ulysses are typically directed outwards from the Sun, suggesting either acceleration extending to high latitudes or efficient cross-field propagation somewhere inside the orbit of Ulysses. Both cosmic ray and SEP observations are consistent with highly efficient transport of energetic charged particles between the equatorial and polar regions and across the mean Interplanetary Magnetic Fields in the inner heliosphere. Key words. Interplanetary physics (cosmic rays) – Solar physics, astrophysics and astronomy (energetic particles; flares and mass ejections)
N V Pogorelov - One of the best experts on this subject based on the ideXlab platform.
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three dimensional features of the outer heliosphere due to coupling between the interstellar and Interplanetary Magnetic Fields iv solar cycle model based on ulysses observations
The Astrophysical Journal, 2013Co-Authors: N V Pogorelov, S N Borovikov, S T Suess, D J Mccomas, R W Ebert, G P ZankAbstract:The solar cycle has a profound influence on the solar wind (SW) interaction with the local interstellar medium (LISM) on more than one timescales. Also, there are substantial differences in individual solar cycle lengths and SW behavior within them. The presence of a slow SW belt, with a variable latitudinal extent changing within each solar cycle from rather small angles to 90 Degree-Sign , separated from the fast wind that originates at coronal holes substantially affects plasma in the inner heliosheath (IHS)-the SW region between the termination shock (TS) and the heliopause (HP). The solar cycle may be the reason why the complicated flow structure is observed in the IHS by Voyager 1. In this paper, we show that a substantial decrease in the SW ram pressure observed by Ulysses between the TS crossings by Voyager 1 and 2 contributes significantly to the difference in the heliocentric distances at which these crossings occurred. The Ulysses spacecraft is the source of valuable information about the three-dimensional and time-dependent properties of the SW. Its unique fast latitudinal scans of the SW regions make it possible to create a solar cycle model based on the spacecraft in situ measurements. On the basis of more » our analysis of the Ulysses data over the entire life of the mission, we generated time-dependent boundary conditions at 10 AU from the Sun and applied our MHD-neutral model to perform a numerical simulation of the SW-LISM interaction. We analyzed the global variations in the interaction pattern, the excursions of the TS and the HP, and the details of the plasma and Magnetic field distributions in the IHS. Numerical results are compared with Voyager data as functions of time in the spacecraft frame. We discuss solar cycle effects which may be reasons for the recent decrease in the TS particles (ions accelerated to anomalous cosmic-ray energies) flux observed by Voyager 1. « less
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heliospheric asymmetries due to the action of the interstellar Magnetic field
Advances in Space Research, 2009Co-Authors: N V Pogorelov, G P Zank, J W Mitchell, J Heerikhuisen, Iver H. CairnsAbstract:We discuss the asymmetry of the heliospheric discontinuities obtained from the analysis of 3D modeling of the solar wind (SW) interaction with local interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the flow of neutral particles is described by the Boltzmann equation. The emphasis is made on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the interstellar and Interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms whose transport through the heliosphere is modeled kinetically, using a Monte Carlo approach. We show that the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM is highly anisotropic and evaluate a possible angle between the hydrogen deflection plane measured in the SOHO SWAN experiment and the plane containing the ISMF and LISM velocity vectors for different ISMF strengths. It is shown that the ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric difference observed during its crossing by the Voyager 1 and Voyager 2 spacecraft, which however results in a larger discrepancy between the calculated and observed velocity distributions. The effect of a strong ISMF on the distribution of plasma quantities in the inner heliosheath and on 2–3 kHz radio emission is discussed.
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three dimensional features of the outer heliosphere due to coupling between the interstellar and Interplanetary Magnetic Fields iii the effects of solar rotation and activity cycle
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, G P Zank, S N Borovikov, Tatsuki OginoAbstract:We investigate the effects of the 11 year solar cycle and 25 day rotation period of the Sun on the interaction of the solar wind (SW) with the local interstellar medium (LISM). Our models take into account the partially ionized character of the LISM and include momentum and energy transfer between the ionized and neutral components. We assume that the interstellar Magnetic field vector belongs to the hydrogen deflection plane as discovered in the SOHO SWAN experiment. This plane is inclined at an angle of about 60° toward the ecliptic plane of the Sun, as suggested in recent publications relating the local interstellar cloud properties to the radio emission observed by Voyager 1. It is assumed that the latitudinal extent of the boundary between the slow and fast SW regions, as well as the angle between the Sun's rotation and Magnetic-dipole axes, are periodic functions of time, while the polarity of the interstellar Magnetic field changes sign every 11 years at the solar maximum. The global variation of the SW-LISM interaction pattern, the excursions of the termination shock and the heliopause, and parameter distributions in certain directions are investigated. The analysis of the behavior of the wavy heliospheric current sheet in the supersonic SW region shows the importance of neutral atoms on its dynamics.
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heliospheric asymmetries and 2 3 khz radio emission under strong interstellar Magnetic field conditions
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, Iver H. Cairns, J W Mitchell, J Heerikhuisen, G P ZankAbstract:We discuss the asymmetry of the major heliospheric discontinuities obtained from the analysis of three-dimensional modeling of the solar wind interaction with the local interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the transport of neutral particles is described by the Boltzmann equation. The emphasis is on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the interstellar and Interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms. It is shown that an ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric distances observed by the Voyager 1 and Voyager 2 spacecraft. We analyze the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM and conclude that it remains within the range measured in the SOHO SWAN experiment. The impact is analyzed of a strong ISMF on the 2-3 kHz radio emission observed by the Voyager spacecraft, using new estimates of the radio emission conditions.
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Influence of the Interstellar Magnetic Field and Neutrals on the Shape of the Outer Heliosphere
Space Science Reviews, 2009Co-Authors: N V Pogorelov, G P Zank, J Heerikhuisen, S N BorovikovAbstract:Formed as a result of the solar wind (SW) interaction with the circum-heliospheric interstellar medium (CHISM), the outer heliosphere is generically three-dimensional because of the SW asphericity and the action of the interstellar and Interplanetary Magnetic Fields (ISMF and IMF). In this paper we show that charge exchange between neutral and charged components of the SW–CHISM plasmas plays a dominant role not only in determining the geometrical size of the heliosphere, but also in the modulation of Magnetic-field-induced asymmetries. More specifically, charge exchange between SW and CHISM protons and primary neutrals of interstellar origin always acts to decrease the asymmetry of the termination shock and the heliopause, which can otherwise be very large. This is particularly pronounced because the ionization ratio of the CHISM plasma is rather low. To investigate the deflection of the CHISM neutral hydrogen flow in the inner heliosphere from its original orientation in the unperturbed CHISM, we create two-dimensional neutral H velocity distributions in the inner heliosphere within a 45-degree circular conical surface with the apex at the Sun and the axis parallel to the interstellar flow vector. It is shown that the distribution of deflections is very anisotropic, that is, the most probable orientation of the H-atom velocity differs from its average direction. We show that the average deflection of the H-atom flow, for reasonable ISMF strengths, occurs mostly in the plane formed by the ISMF and CHISM velocity vectors at infinity. The possibility that the ISMF orientation may influence the 2–3 kHz radio emission, which is believed to originate in the outer heliosheath, is discussed.
H K Rassoul - One of the best experts on this subject based on the ideXlab platform.
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Stochastic Propagation of Solar Energetic Particles in Coronal and Interplanetary Magnetic Fields
Journal of Physics: Conference Series, 2019Co-Authors: Ming Zhang, Lulu Zhao, H K RassoulAbstract:This paper describes a method of simulating solar energetic particle propagation through the Magnetic Fields of the solar corona and Interplanetary medium. The simulation code is based on the focus transport equation of energetic particles in 3-d Magnetic Fields, which contains all the particle transport mechanisms, including streaming, convection, gradient/curvature drift, adiabatic focusing, pitch angle scattering by Alfvenic Magnetic field fluctuations and perpendicular diffusion due to the random walk of field lines. In the simulation, particles are injected at their source in the corona, and their guiding center trajectories are calculated using stochastic differential equations. Because of the vastly different time scales of particle transport mechanisms included in the equation, we use the 4-th order Runge-Kutta method to integrate the particle streaming and adiabatic focusing terms, while the stochastic terms of pitch angle scattering and perpendicular diffusion are integrated with the Euler scheme. The model is applied to the 2017 September 10 solar energetic particle event. With perpendicular diffusion, we are able to explain SEP observations from Earth and STEREO-A. A pattern of SEP precipitation on the solar surface is also predicted.
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propagation of solar energetic particles in three dimensional Interplanetary Magnetic Fields
The Astrophysical Journal, 2009Co-Authors: Ming Zhang, H K RassoulAbstract:This paper presents a model calculation of solar energetic particle propagation in a three-dimensional Interplanetary Magnetic field. The model includes essentially all the particle transport mechanisms: streaming along Magnetic field lines, convection with the solar wind, pitch-angle diffusion, focusing by the inhomogeneous Interplanetary Magnetic field, perpendicular diffusion, and pitch-angle dependent adiabatic cooling by the expanding solar wind. We solve the Fokker–Planck transport equation with simulation of backward stochastic processes in a fixed reference frame in which any spacecraft is roughly stationary. As an example we model the propagation of those high-energy (E 10 MeV) solar energetic particles in gradual events that are accelerated by large coronal mass ejection shocks in the corona and released near the Sun into Interplanetary space of a Parker spiral Magnetic field. Modeled with different scenarios, the source of solar energetic particles can have a full or various limited coverages of latitude and longitude on the solar surface. We compute the long-term time profiles of particle flux and anisotropy at various locations in the heliosphere up to 3 AU, from the ecliptic to high latitudes. Features from particle perpendicular diffusion are revealed. Our simulation reproduces the observed reservoir phenomenon of solar energetic particles with constraints on either solar particle source or the magnitude of perpendicular diffusion.
G P Zank - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional features of the outer heliosphere due to coupling between the interstellar and Interplanetary Magnetic Fields. II. The presence of neutral hydrogen atoms, Astrophys
2014Co-Authors: Nikolai V Pogorelov, G P Zank, Tatsuki OginoAbstract:We investigate the effects of coupling the interstellar and Interplanetary Magnetic Fields (ISMF and IMF) at the heliospheric interface while taking into account the momentum and energy transfer between the plasma and neutral components of the interacting solar wind (SW) and local interstellar medium (LISM). Investigation is performed on the basis of the multifluid model that treats different populations of neutral particles as fluids governed by separate sets of the Euler equations. As the properties of the local interstellar cloud (LIC) are rather poorly examined, with the exception of the interstellar plasma velocity and temperature, we assume several possible orientations of the ISMF. In particular, the case is considered where an ISMF vector is perpendicular to the LISM velocity vector and inclined at an angle of 60 toward the ecliptic plane of the Sun, as suggested in recent publications relating LIC properties to the radio emission observed byVoyager 1. Special attention is paid to the distribution ofMagnetic Fields that can affect the cosmic-ray modulation throughout the heliosphere and the possibility of the heliospheric current sheet bending into one of the hemispheres. Differences are discussed between ideal MHD and multifluid calculations. Possibilities are analyzed for the IMF lines to cross the termination shock multiple times. Parameters are determined that affect the divergence between the neutral hydrogen and helium streamlines in the inner heliosphere. Subject headinggs: ISM: kinematics and dynamics — ISM: Magnetic Fields — MHD — solar wind Online material: color figures 1
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three dimensional features of the outer heliosphere due to coupling between the interstellar and Interplanetary Magnetic Fields iv solar cycle model based on ulysses observations
The Astrophysical Journal, 2013Co-Authors: N V Pogorelov, S N Borovikov, S T Suess, D J Mccomas, R W Ebert, G P ZankAbstract:The solar cycle has a profound influence on the solar wind (SW) interaction with the local interstellar medium (LISM) on more than one timescales. Also, there are substantial differences in individual solar cycle lengths and SW behavior within them. The presence of a slow SW belt, with a variable latitudinal extent changing within each solar cycle from rather small angles to 90 Degree-Sign , separated from the fast wind that originates at coronal holes substantially affects plasma in the inner heliosheath (IHS)-the SW region between the termination shock (TS) and the heliopause (HP). The solar cycle may be the reason why the complicated flow structure is observed in the IHS by Voyager 1. In this paper, we show that a substantial decrease in the SW ram pressure observed by Ulysses between the TS crossings by Voyager 1 and 2 contributes significantly to the difference in the heliocentric distances at which these crossings occurred. The Ulysses spacecraft is the source of valuable information about the three-dimensional and time-dependent properties of the SW. Its unique fast latitudinal scans of the SW regions make it possible to create a solar cycle model based on the spacecraft in situ measurements. On the basis of more » our analysis of the Ulysses data over the entire life of the mission, we generated time-dependent boundary conditions at 10 AU from the Sun and applied our MHD-neutral model to perform a numerical simulation of the SW-LISM interaction. We analyzed the global variations in the interaction pattern, the excursions of the TS and the HP, and the details of the plasma and Magnetic field distributions in the IHS. Numerical results are compared with Voyager data as functions of time in the spacecraft frame. We discuss solar cycle effects which may be reasons for the recent decrease in the TS particles (ions accelerated to anomalous cosmic-ray energies) flux observed by Voyager 1. « less
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heliospheric asymmetries due to the action of the interstellar Magnetic field
Advances in Space Research, 2009Co-Authors: N V Pogorelov, G P Zank, J W Mitchell, J Heerikhuisen, Iver H. CairnsAbstract:We discuss the asymmetry of the heliospheric discontinuities obtained from the analysis of 3D modeling of the solar wind (SW) interaction with local interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the flow of neutral particles is described by the Boltzmann equation. The emphasis is made on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the interstellar and Interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms whose transport through the heliosphere is modeled kinetically, using a Monte Carlo approach. We show that the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM is highly anisotropic and evaluate a possible angle between the hydrogen deflection plane measured in the SOHO SWAN experiment and the plane containing the ISMF and LISM velocity vectors for different ISMF strengths. It is shown that the ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric difference observed during its crossing by the Voyager 1 and Voyager 2 spacecraft, which however results in a larger discrepancy between the calculated and observed velocity distributions. The effect of a strong ISMF on the distribution of plasma quantities in the inner heliosheath and on 2–3 kHz radio emission is discussed.
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three dimensional features of the outer heliosphere due to coupling between the interstellar and Interplanetary Magnetic Fields iii the effects of solar rotation and activity cycle
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, G P Zank, S N Borovikov, Tatsuki OginoAbstract:We investigate the effects of the 11 year solar cycle and 25 day rotation period of the Sun on the interaction of the solar wind (SW) with the local interstellar medium (LISM). Our models take into account the partially ionized character of the LISM and include momentum and energy transfer between the ionized and neutral components. We assume that the interstellar Magnetic field vector belongs to the hydrogen deflection plane as discovered in the SOHO SWAN experiment. This plane is inclined at an angle of about 60° toward the ecliptic plane of the Sun, as suggested in recent publications relating the local interstellar cloud properties to the radio emission observed by Voyager 1. It is assumed that the latitudinal extent of the boundary between the slow and fast SW regions, as well as the angle between the Sun's rotation and Magnetic-dipole axes, are periodic functions of time, while the polarity of the interstellar Magnetic field changes sign every 11 years at the solar maximum. The global variation of the SW-LISM interaction pattern, the excursions of the termination shock and the heliopause, and parameter distributions in certain directions are investigated. The analysis of the behavior of the wavy heliospheric current sheet in the supersonic SW region shows the importance of neutral atoms on its dynamics.
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heliospheric asymmetries and 2 3 khz radio emission under strong interstellar Magnetic field conditions
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, Iver H. Cairns, J W Mitchell, J Heerikhuisen, G P ZankAbstract:We discuss the asymmetry of the major heliospheric discontinuities obtained from the analysis of three-dimensional modeling of the solar wind interaction with the local interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the transport of neutral particles is described by the Boltzmann equation. The emphasis is on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the interstellar and Interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms. It is shown that an ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric distances observed by the Voyager 1 and Voyager 2 spacecraft. We analyze the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM and conclude that it remains within the range measured in the SOHO SWAN experiment. The impact is analyzed of a strong ISMF on the 2-3 kHz radio emission observed by the Voyager spacecraft, using new estimates of the radio emission conditions.
H Q He - One of the best experts on this subject based on the ideXlab platform.
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propagation of solar energetic particles in three dimensional Interplanetary Magnetic Fields radial dependence of peak intensities
The Astrophysical Journal, 2017Co-Authors: H Q He, Guiping ZhouAbstract:A functional form , where R is the radial distance of a spacecraft, was usually used to model the radial dependence of peak intensities of solar energetic particles (SEPs). In this work, the five-dimensional Fokker–Planck transport equation incorporating perpendicular diffusion is numerically solved to investigate the radial dependence of SEP peak intensities. We consider two different scenarios for the distribution of a spacecraft fleet: (1) along the radial direction line and (2) along the Parker Magnetic field line. We find that the index α in the above expression varies in a wide range, primarily depending on the properties (e.g., location and coverage) of SEP sources and on the longitudinal and latitudinal separations between the sources and the Magnetic foot points of the observers. Particularly, whether the Magnetic foot point of the observer is located inside or outside the SEP source is a crucial factor determining the values of index α. A two-phase phenomenon is found in the radial dependence of peak intensities. The "position" of the break point (transition point/critical point) is determined by the Magnetic connection status of the observers. This finding suggests that a very careful examination of the Magnetic connection between the SEP source and each spacecraft should be taken in the observational studies. We obtain a lower limit of for empirically modeling the radial dependence of SEP peak intensities. Our findings in this work can be used to explain the majority of the previous multispacecraft survey results, and especially to reconcile the different or conflicting empirical values of the index α in the literature.
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propagation of solar energetic particles in three dimensional Interplanetary Magnetic Fields in view of characteristics of sources
The Astrophysical Journal, 2011Co-Authors: H Q He, Ming ZhangAbstract:In this paper, a model of solar energetic particle (SEP) propagation in the three-dimensional Parker Interplanetary Magnetic field is calculated numerically. We study the effects of the different aspects of particle sources on the solar surface, which include the source location, coverage of latitude and longitude, and spatial distribution of source particle intensity, on propagation of SEPs with both parallel and perpendicular diffusion. We compute the particle flux and anisotropy profiles at different observation locations in the heliosphere. From our calculations, we find that the observation location relative to the latitudinal and longitudinal coverage of particle source has the strongest effects on particle flux and anisotropy profiles observed by a spacecraft. When a spacecraft is directly connected to the solar sources by the Interplanetary Magnetic field lines, the observed particle fluxes are larger than when the spacecraft is not directly connected. This paper focuses on the situations when a spacecraft is not connected to the particle sources on the solar surface. We find that when the Magnetic footpoint of the spacecraft is farther away from the source, the observed particle flux is smaller and its onset and maximum intensity occur later. When the particle source covers a larger range of latitude and longitude, the observed particle flux is larger and appears earlier. There is east-west azimuthal asymmetry in SEP profiles even when the source distribution is east-west symmetric. However, the detail of particle spatial distribution inside the source does not affect the profile of the SEP flux very much. When the Magnetic footpoint of the spacecraft is significantly far away from the particle source, the anisotropy of particles in the early stage of an SEP event points toward the Sun, which indicates that the first arriving particles come from outside of the observer through perpendicular diffusion at large radial distances.
