Peter Gary - Academia.edu (original) (raw)

Papers by Peter Gary

Research paper thumbnail of Resonant Heating and Acceleration of Ions in Coronal Holes by High-Frequency Wave Spectrum

Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats ... more Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats and accelerates the ions in the solar wind. Velocity distributions of minor ions derived from SOHO UVCS observations in coronal holes indicate that the minor ion temperature anisotropy >10 and outflow speeds is higher then the solar wind protons. Using 1D hybrid code we investigate the effects of differential flow and anisotropy on the stability of the solar wind plasma. We investigate the heating and the acceleration of the solar wind plasma ions by including an input spectrum of the form f-1 and f-5/3. We find that the ion heating strongly depends on the power contained in the frequency range of the power-law spectrum that can resonate with the ions. The heating also depends on the plasma beta , and the abundance of the minor ions. We investigate the self-consistent fluctuations spectrum generated by the response of the ions. We have used second-order theory (Gary and Tokar 1985) to evaluate the rates of proton heating, anisotropy formation, and acceleration, and have compared these predictions against the simulation results.

Research paper thumbnail of Electrostatic flow shear instability

Journal of Geophysical Research, 1980

ABSTRACT

Research paper thumbnail of Constraints on the O+5 Anisotropy in the Solar Corona

Astrophys J, 2001

Velocity distributions of O+5 ions derived from Ultraviolet Coronagraph Spectrometer (UVCS) obser... more Velocity distributions of O+5 ions derived from Ultraviolet Coronagraph Spectrometer (UVCS) observations in coronal holes indicate that the O+5 ions are highly anisotropic (T⊥i/T∥i~30-300 at 3.5 Rsolar). The observations provide empirical values for the electron density and the ion temperatures. It is well known that the electromagnetic ion cyclotron instability is driven by temperature anisotropy. The instability leads to the rapid decrease of anisotropy and transfer of part of the kinetic energy of the particles into the magnetic field fluctuations. Here we use linear theory and hybrid simulations combined with the empirical values of the densities and the temperatures to investigate the ion cyclotron instability of the anisotropic minor ions in the coronal hole plasma. We find that an initial O+5 anisotropy of 50 decreases by an order of magnitude within ~300-900 proton cyclotron periods. Thus, the ion cyclotron instability constrains the anisotropy of O+5 ions that can be sustained in the solar corona without continuous perpendicular heating.

Research paper thumbnail of The role of microprocesses in macroscale magnetotail dynamics

Geophysical Monograph Series, 2000

ABSTRACT

Research paper thumbnail of Whistler anisotropy instability: Spectral transfer in a three-dimensional particle-in-cell simulation

Journal of Geophysical Research: Space Physics, 2014

A three-dimensional (3-D) particle-in-cell (PIC) simulation of the whistler anisotropy instabilit... more A three-dimensional (3-D) particle-in-cell (PIC) simulation of the whistler anisotropy instability is carried out for a collisionless, homogeneous, magnetized plasma with e = 0.10. This is the first 3-D PIC simulation of the evolution of enchanced fluctuations from this growing mode driven by an anisotropic electron velocity distribution with T ⟂e ∕T ∥e > 1 where ⟂ and ∥ represent directions perpendicular and parallel to the background magnetic field o , respectively. The early-time magnetic fluctuation spectrum grows with properties reflecting the predictions of linear theory with narrowband maxima at kc∕ e ≃ 1 and × = 0, and a wave vector anisotropy in the sense of k ⟂ << k ∥ . Here e represents the electron plasma frequency. At later times the fluctuations undergo both a forward transfer to shorter wavelengths, also with k ⟂ << k ∥ , and an inverse transfer to longer wavelengths with wave vector anisotropy k ⟂ >> k ∥ . The inverse transfer is consistent with a prediction of nonlinear three-wave coupling theory.

Research paper thumbnail of Electromagnetic ion beam instabilities: II

Physics of Fluids, 1985

ABSTRACT

Research paper thumbnail of Statistical survey of magnetic and velocity fluctuations in the near-Earth plasma sheet: International Sun Earth Explorer (ISEE-2) measurements

Journal of Geophysical Research, 2005

1] International Sun-Earth Explorer (ISEE-2) satellite observations of low-frequency magnetic fie... more 1] International Sun-Earth Explorer (ISEE-2) satellite observations of low-frequency magnetic field and ion velocity fluctuations in the Earth's magnetotail are compared with corresponding observations from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM). Solar activity during these two missions is different and thus also considered. The ISEE-2 analysis is performed on the data taken from satellite passes through the Earth's plasma sheet in 1978 and 1979 near solar maximum. The data is divided into 2298 ten-minute-long intervals where the averages of the magnetic field, ion velocity, and plasma parameter's amplitudes are statistically calculated for each interval. We find no significant dependence of the amplitude of the ion velocity and magnetic field fluctuations on the magnetotail distance or on the distance from the neutral sheet. The correlation coefficient between the geomagnetic activity and the amplitude of both ion velocity and magnetic field fluctuations in the ISEE-2 measurements is smaller than the one found for the AMPTE/IRM passes through the plasma sheet. When comparing the two satellite data sets for the same plasma sheet region, we obtain a significantly higher upper bound for the ISEE-2 fluctuating magnetic field energy density. Our results suggest that the significantly increased magnetic field fluctuation amplitude in the plasma sheet during the ISEE-2 satellite passes is due to the increased solar activity near solar maximum.

Research paper thumbnail of An electrostatic flow shear instability

Journal of Geophysical Research, 1980

ABSTRACT

Research paper thumbnail of Electromagnetic instabilities in the plasma sheet boundary layer

Journal of Geophysical Research, 1989

Plasma and magnetic field data observed during two ISEE crossings of the plasma sheet boundary la... more Plasma and magnetic field data observed during two ISEE crossings of the plasma sheet boundary layer are studied in conjunction with a linear stability theory analysis. The plasma distribution functions exhibit three distinct potential sources of free energy: ion/ion relative drifts, electron/ion relative drifts corresponding to a nonzero field-aligned current, and large ion temperature anisotropies. These observed distributions are used

Research paper thumbnail of The lower hybrid density drift instability with cold plasma

Journal of Geophysical Research, 1981

ABSTRACT

Research paper thumbnail of Microscale anisotropy reduction and macroscale dynamics of the magnetotail

Journal of Geophysical Research, 1995

Anisotropic magnetofluid simulations are used to investigate the influence of several models of a... more Anisotropic magnetofluid simulations are used to investigate the influence of several models of anisotropy reduction on the dynamic evolution of the magnetotail. Two distinct magnetotail dynamic models are studied: a nonresistive simulation driven by an external electric field as a representation of the substorm growth phase, and a resistive simulation with a uniform enhanced resistivity as a representation of the substorm expansive phase. The plasma models include one which is fully isotropic, the double adiabatic model in which pressures parallel and perpendicular to the background magnetic field are completely uncoupled, and a model in which small-scale instabilities impose an upper bound on the anisotropy. In this last model, anisotropies that exceed this bound are reduced on a short Alfvénic timescale. To investigate the transition to the fully isotropic model, a fourth plasma model is studied in which any anisotropy is reduced on the same short timescale. The growth phase magnetotail model is characterized by a localized increase in current density and by a reduction in the magnitude of Bz in the near-Earth neutral sheet; both of these effects are more pronounced for the more isotropic plasma models. For the expansive phase magnetotail model the development of a generalized tearing instability occurs faster and the substorm wedge currents grow stronger when the plasma model is closer to isotropy. In both magnetotail models the plasma anisotropy model strongly influences the spatial variation Bz in the neutral sheet and hence the location where reconnection occurs and a neutral line forms. Both the driven and the unstable anisotropic models develop mirror-type anisotropies (p⊥>p||) in the (low beta or low current density) boundary regions of the plasma sheet and the adjacent lobes, while the (high beta or high current density) center region of the plasma/current sheet remains close to isotropy. .

Research paper thumbnail of Whistler instability: Electron anisotropy upper bound

Journal of Geophysical Research, 1996

ABSTRACT

Research paper thumbnail of Identification of low-frequency magnetosheath waves

Journal of Geophysical Research, 1998

Four low-frequency modes may propagate in a high-beta, nearly bi-Maxwelltan plasma, the magnetoso... more Four low-frequency modes may propagate in a high-beta, nearly bi-Maxwelltan plasma, the magnetosonic, Alfv6n, ion acoustic, and mirror modes. This study uses a procedure based on linear Vlasov theory for the identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation, is calculated which characterizes the difference between the theoretical transport ratios of a particular mode and the observed ratios. As well as determining the mode that best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Unfortunately, a unique identification is not always possible because of problems discussed herein. One problem is that the parallel phase ratio (related to the phase angle between density and parallel magnetic fluctuations) is often not well defined. Using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module spacecraft, we calculate the mode deviations and identify the modes observed in the magnetosheath. The quasi-perpendicular (with wave vector at a large angle to the background magnetic field) mirror mode is clearly identified in the inner (close to the magnetopause) and middle magnetosheath. The quasi-parallel mirror mode may be observed in the inner magnetosheath, but that identification is not certain. Alfv6n-like modes are observed for one event in the outer magnetosheath (near the bow shock) and are probably observed in two others. involved the use of kinetic theory rather than MHD, the attribution of equal weight to the information from dif-ferent transport ratios rather than a decision tree, the use of the Alfvdn ratio rather than Song et al.'s Doppler ratio, and allowance for the possibility of modes such as the quasi-parallel (wave vector k approximately parallel to the background magnetic field B0) mirror and ion acoustic modes. (See Schwartz et al. [1996] for a discussion of the different methods.). Denton el al.

Research paper thumbnail of Electromagnetic heavy-ion/proton instabilities

Journal of Geophysical Research, 1999

Ion/ion instabilities are driven by the relative velocity 2 1 , of two distinct ion components. T... more Ion/ion instabilities are driven by the relative velocity 2 1 , of two distinct ion components. This manuscript reports linear theory and simulation studies of electromagnetic ion/ion instabilities for a warm proton component streaming against a cool, heavy ion component in a homogeneous, magnetized plasma in which 2 1 , is parallel or antiparallel to the background magnetic field. Under these conditions linear Vlasov dispersion theory predicts that the fastest growing mode is usually the right-hand polarized proton resonant instability. Two-dimensional initial value hybrid simulations of this growing mode are carried out, yielding scaling relations for the maximum fluctuating magnetic field energy density and the proton pickup time. The latter is proportional to the inverse of the maximum growth rate for a wide range of plasma parameters.

Research paper thumbnail of Proton temperature anisotropy constraint in the solar wind: ACE observations

Geophysical Research Letters, 2001

Geophysical Research Letters publishes short, concise research letters that present scientific ad... more Geophysical Research Letters publishes short, concise research letters that present scientific advances that are likely to have immediate influence on the research of other investigators. GRL letters can focus on a specific discipline or apply broadly to the geophysical science community ...

Research paper thumbnail of Hybrid Simulations of the Heliospheric Termination Shock

We use the Los Alamos hybrid plasma code to simulate the quasi-perpendicular heliospheric termina... more We use the Los Alamos hybrid plasma code to simulate the quasi-perpendicular heliospheric termination shock in one spatial dimension. The purpose of this study is to shed light on the shock-heated thermal and suprathermal populations in the heliosheath that have not yet been measured directly. Our study will make predictions that will be compared to energetic neutral atom (ENA) observations to be made by the Interstellar Boundary Explorer (IBEX) Mission after its launch in 2008. The ENAs to be measured by IBEX are generated from charge exchange of interstellar neutrals with protons heated at the termination shock. We use the simulations to characterize the downstream proton velocity distribution as a function of Alfven Mach number and plasma beta for a range of parameters expected at the termination shock. These distributions will then be used in a model to predict the fluxes of energetic neutrals to be observed by IBEX.

Research paper thumbnail of Hybrid simulations of plasma transport by Kelvin-Helmholtz instability at the magnetopause: magnetic shear

ABSTRACT Two-dimensional hybrid (kinetic ions and massless fluid electrons) simulations of the Ke... more ABSTRACT Two-dimensional hybrid (kinetic ions and massless fluid electrons) simulations of the Kelvin-Helmholtz instability (KHI) for a magnetopause configuration with a varying density jump and magnetic shear across the boundary are carried out to examine how the transport of magnetosheath plasma into the magnetosphere is affected by these conditions. Low magnetic shear conditions where the magnetosheath magnetic field is within 30° of northward is included in the simulations because KHI is thought to be important for plasma transport only for northward or near-northward interplanetary magnetic field orientations. The simulations show that coherent vortices can grow for these near-northward angles and that they are sometimes more coherent than for pure northward conditions because the turbulence which breaks down these vortices is reduced when there are magnetic tension forces. With increasing magnetic shear angle and increasing density jump, the growth rate is reduced, and the vortices do not grow to as large of a size, which reduces the plasma transport. By tracking the individual particle motions, diffusion coefficients can be obtained for the system, where the diffusion is not classical in nature but instead has a time dependence resulting from both the increasingly large-scale vortex motion and the small-scale turbulence generated in the breakdown of the instabilities. Results indicate that diffusion on the order of 109 m2/s could possibly be generated by KHI on the flanks of the magnetosphere.

Research paper thumbnail of Ion heating and energy partition at the heliospheric termination shock: hybrid simulations and analytical model

Journal of Geophysical Research Atmospheres, 2009

ABSTRACT

Research paper thumbnail of Kinetic physics of the mirror instability

Journal of Geophysical Research, 1993

Kinetic mechanisms for the growth and saturation of the mirror instability are described using on... more Kinetic mechanisms for the growth and saturation of the mirror instability are described using one-dimensional hybrid simulations. Two parameter regimes are considered. In the first regime, a relatively small ion anisotropy excites a slowly growing instability that produces small-amplitude waves; most ions respond to the waves as an adiabatic fluid. In the second regime a large anisotropy excites a rapidly growing instability that generates large-amplitude waves; the response of many ions in this case is nonadiabatic. The difference in ion response is due to the relative importance of two ion populations, resonant and nonresonant. Resonant ions, those ions with low velocities parallel to the background magnetic field, contribute to the growth of the instability as a result of their gyrointeractions with the noncoplanar component of the waves electric field and respond to the mirror waves nonadiabatically. Nonreasonant ions, those with large parallel velocities, respond as an adiabatic fluid. In both regimes, ion anisotropy is reduced by means of the magnetic mirror force; in the second regime, the anisotropy reduction reduces the free energy available for wave growth and leads to the saturation of the mirror instability.

Research paper thumbnail of Alfv�n-cyclotron scattering of solar wind ions: Hybrid simulations

Journal of Geophysical Research, 2006

Research paper thumbnail of Resonant Heating and Acceleration of Ions in Coronal Holes by High-Frequency Wave Spectrum

Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats ... more Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats and accelerates the ions in the solar wind. Velocity distributions of minor ions derived from SOHO UVCS observations in coronal holes indicate that the minor ion temperature anisotropy >10 and outflow speeds is higher then the solar wind protons. Using 1D hybrid code we investigate the effects of differential flow and anisotropy on the stability of the solar wind plasma. We investigate the heating and the acceleration of the solar wind plasma ions by including an input spectrum of the form f-1 and f-5/3. We find that the ion heating strongly depends on the power contained in the frequency range of the power-law spectrum that can resonate with the ions. The heating also depends on the plasma beta , and the abundance of the minor ions. We investigate the self-consistent fluctuations spectrum generated by the response of the ions. We have used second-order theory (Gary and Tokar 1985) to evaluate the rates of proton heating, anisotropy formation, and acceleration, and have compared these predictions against the simulation results.

Research paper thumbnail of Electrostatic flow shear instability

Journal of Geophysical Research, 1980

ABSTRACT

Research paper thumbnail of Constraints on the O+5 Anisotropy in the Solar Corona

Astrophys J, 2001

Velocity distributions of O+5 ions derived from Ultraviolet Coronagraph Spectrometer (UVCS) obser... more Velocity distributions of O+5 ions derived from Ultraviolet Coronagraph Spectrometer (UVCS) observations in coronal holes indicate that the O+5 ions are highly anisotropic (T⊥i/T∥i~30-300 at 3.5 Rsolar). The observations provide empirical values for the electron density and the ion temperatures. It is well known that the electromagnetic ion cyclotron instability is driven by temperature anisotropy. The instability leads to the rapid decrease of anisotropy and transfer of part of the kinetic energy of the particles into the magnetic field fluctuations. Here we use linear theory and hybrid simulations combined with the empirical values of the densities and the temperatures to investigate the ion cyclotron instability of the anisotropic minor ions in the coronal hole plasma. We find that an initial O+5 anisotropy of 50 decreases by an order of magnitude within ~300-900 proton cyclotron periods. Thus, the ion cyclotron instability constrains the anisotropy of O+5 ions that can be sustained in the solar corona without continuous perpendicular heating.

Research paper thumbnail of The role of microprocesses in macroscale magnetotail dynamics

Geophysical Monograph Series, 2000

ABSTRACT

Research paper thumbnail of Whistler anisotropy instability: Spectral transfer in a three-dimensional particle-in-cell simulation

Journal of Geophysical Research: Space Physics, 2014

A three-dimensional (3-D) particle-in-cell (PIC) simulation of the whistler anisotropy instabilit... more A three-dimensional (3-D) particle-in-cell (PIC) simulation of the whistler anisotropy instability is carried out for a collisionless, homogeneous, magnetized plasma with e = 0.10. This is the first 3-D PIC simulation of the evolution of enchanced fluctuations from this growing mode driven by an anisotropic electron velocity distribution with T ⟂e ∕T ∥e > 1 where ⟂ and ∥ represent directions perpendicular and parallel to the background magnetic field o , respectively. The early-time magnetic fluctuation spectrum grows with properties reflecting the predictions of linear theory with narrowband maxima at kc∕ e ≃ 1 and × = 0, and a wave vector anisotropy in the sense of k ⟂ << k ∥ . Here e represents the electron plasma frequency. At later times the fluctuations undergo both a forward transfer to shorter wavelengths, also with k ⟂ << k ∥ , and an inverse transfer to longer wavelengths with wave vector anisotropy k ⟂ >> k ∥ . The inverse transfer is consistent with a prediction of nonlinear three-wave coupling theory.

Research paper thumbnail of Electromagnetic ion beam instabilities: II

Physics of Fluids, 1985

ABSTRACT

Research paper thumbnail of Statistical survey of magnetic and velocity fluctuations in the near-Earth plasma sheet: International Sun Earth Explorer (ISEE-2) measurements

Journal of Geophysical Research, 2005

1] International Sun-Earth Explorer (ISEE-2) satellite observations of low-frequency magnetic fie... more 1] International Sun-Earth Explorer (ISEE-2) satellite observations of low-frequency magnetic field and ion velocity fluctuations in the Earth's magnetotail are compared with corresponding observations from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM). Solar activity during these two missions is different and thus also considered. The ISEE-2 analysis is performed on the data taken from satellite passes through the Earth's plasma sheet in 1978 and 1979 near solar maximum. The data is divided into 2298 ten-minute-long intervals where the averages of the magnetic field, ion velocity, and plasma parameter's amplitudes are statistically calculated for each interval. We find no significant dependence of the amplitude of the ion velocity and magnetic field fluctuations on the magnetotail distance or on the distance from the neutral sheet. The correlation coefficient between the geomagnetic activity and the amplitude of both ion velocity and magnetic field fluctuations in the ISEE-2 measurements is smaller than the one found for the AMPTE/IRM passes through the plasma sheet. When comparing the two satellite data sets for the same plasma sheet region, we obtain a significantly higher upper bound for the ISEE-2 fluctuating magnetic field energy density. Our results suggest that the significantly increased magnetic field fluctuation amplitude in the plasma sheet during the ISEE-2 satellite passes is due to the increased solar activity near solar maximum.

Research paper thumbnail of An electrostatic flow shear instability

Journal of Geophysical Research, 1980

ABSTRACT

Research paper thumbnail of Electromagnetic instabilities in the plasma sheet boundary layer

Journal of Geophysical Research, 1989

Plasma and magnetic field data observed during two ISEE crossings of the plasma sheet boundary la... more Plasma and magnetic field data observed during two ISEE crossings of the plasma sheet boundary layer are studied in conjunction with a linear stability theory analysis. The plasma distribution functions exhibit three distinct potential sources of free energy: ion/ion relative drifts, electron/ion relative drifts corresponding to a nonzero field-aligned current, and large ion temperature anisotropies. These observed distributions are used

Research paper thumbnail of The lower hybrid density drift instability with cold plasma

Journal of Geophysical Research, 1981

ABSTRACT

Research paper thumbnail of Microscale anisotropy reduction and macroscale dynamics of the magnetotail

Journal of Geophysical Research, 1995

Anisotropic magnetofluid simulations are used to investigate the influence of several models of a... more Anisotropic magnetofluid simulations are used to investigate the influence of several models of anisotropy reduction on the dynamic evolution of the magnetotail. Two distinct magnetotail dynamic models are studied: a nonresistive simulation driven by an external electric field as a representation of the substorm growth phase, and a resistive simulation with a uniform enhanced resistivity as a representation of the substorm expansive phase. The plasma models include one which is fully isotropic, the double adiabatic model in which pressures parallel and perpendicular to the background magnetic field are completely uncoupled, and a model in which small-scale instabilities impose an upper bound on the anisotropy. In this last model, anisotropies that exceed this bound are reduced on a short Alfvénic timescale. To investigate the transition to the fully isotropic model, a fourth plasma model is studied in which any anisotropy is reduced on the same short timescale. The growth phase magnetotail model is characterized by a localized increase in current density and by a reduction in the magnitude of Bz in the near-Earth neutral sheet; both of these effects are more pronounced for the more isotropic plasma models. For the expansive phase magnetotail model the development of a generalized tearing instability occurs faster and the substorm wedge currents grow stronger when the plasma model is closer to isotropy. In both magnetotail models the plasma anisotropy model strongly influences the spatial variation Bz in the neutral sheet and hence the location where reconnection occurs and a neutral line forms. Both the driven and the unstable anisotropic models develop mirror-type anisotropies (p⊥>p||) in the (low beta or low current density) boundary regions of the plasma sheet and the adjacent lobes, while the (high beta or high current density) center region of the plasma/current sheet remains close to isotropy. .

Research paper thumbnail of Whistler instability: Electron anisotropy upper bound

Journal of Geophysical Research, 1996

ABSTRACT

Research paper thumbnail of Identification of low-frequency magnetosheath waves

Journal of Geophysical Research, 1998

Four low-frequency modes may propagate in a high-beta, nearly bi-Maxwelltan plasma, the magnetoso... more Four low-frequency modes may propagate in a high-beta, nearly bi-Maxwelltan plasma, the magnetosonic, Alfv6n, ion acoustic, and mirror modes. This study uses a procedure based on linear Vlasov theory for the identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation, is calculated which characterizes the difference between the theoretical transport ratios of a particular mode and the observed ratios. As well as determining the mode that best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Unfortunately, a unique identification is not always possible because of problems discussed herein. One problem is that the parallel phase ratio (related to the phase angle between density and parallel magnetic fluctuations) is often not well defined. Using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module spacecraft, we calculate the mode deviations and identify the modes observed in the magnetosheath. The quasi-perpendicular (with wave vector at a large angle to the background magnetic field) mirror mode is clearly identified in the inner (close to the magnetopause) and middle magnetosheath. The quasi-parallel mirror mode may be observed in the inner magnetosheath, but that identification is not certain. Alfv6n-like modes are observed for one event in the outer magnetosheath (near the bow shock) and are probably observed in two others. involved the use of kinetic theory rather than MHD, the attribution of equal weight to the information from dif-ferent transport ratios rather than a decision tree, the use of the Alfvdn ratio rather than Song et al.'s Doppler ratio, and allowance for the possibility of modes such as the quasi-parallel (wave vector k approximately parallel to the background magnetic field B0) mirror and ion acoustic modes. (See Schwartz et al. [1996] for a discussion of the different methods.). Denton el al.

Research paper thumbnail of Electromagnetic heavy-ion/proton instabilities

Journal of Geophysical Research, 1999

Ion/ion instabilities are driven by the relative velocity 2 1 , of two distinct ion components. T... more Ion/ion instabilities are driven by the relative velocity 2 1 , of two distinct ion components. This manuscript reports linear theory and simulation studies of electromagnetic ion/ion instabilities for a warm proton component streaming against a cool, heavy ion component in a homogeneous, magnetized plasma in which 2 1 , is parallel or antiparallel to the background magnetic field. Under these conditions linear Vlasov dispersion theory predicts that the fastest growing mode is usually the right-hand polarized proton resonant instability. Two-dimensional initial value hybrid simulations of this growing mode are carried out, yielding scaling relations for the maximum fluctuating magnetic field energy density and the proton pickup time. The latter is proportional to the inverse of the maximum growth rate for a wide range of plasma parameters.

Research paper thumbnail of Proton temperature anisotropy constraint in the solar wind: ACE observations

Geophysical Research Letters, 2001

Geophysical Research Letters publishes short, concise research letters that present scientific ad... more Geophysical Research Letters publishes short, concise research letters that present scientific advances that are likely to have immediate influence on the research of other investigators. GRL letters can focus on a specific discipline or apply broadly to the geophysical science community ...

Research paper thumbnail of Hybrid Simulations of the Heliospheric Termination Shock

We use the Los Alamos hybrid plasma code to simulate the quasi-perpendicular heliospheric termina... more We use the Los Alamos hybrid plasma code to simulate the quasi-perpendicular heliospheric termination shock in one spatial dimension. The purpose of this study is to shed light on the shock-heated thermal and suprathermal populations in the heliosheath that have not yet been measured directly. Our study will make predictions that will be compared to energetic neutral atom (ENA) observations to be made by the Interstellar Boundary Explorer (IBEX) Mission after its launch in 2008. The ENAs to be measured by IBEX are generated from charge exchange of interstellar neutrals with protons heated at the termination shock. We use the simulations to characterize the downstream proton velocity distribution as a function of Alfven Mach number and plasma beta for a range of parameters expected at the termination shock. These distributions will then be used in a model to predict the fluxes of energetic neutrals to be observed by IBEX.

Research paper thumbnail of Hybrid simulations of plasma transport by Kelvin-Helmholtz instability at the magnetopause: magnetic shear

ABSTRACT Two-dimensional hybrid (kinetic ions and massless fluid electrons) simulations of the Ke... more ABSTRACT Two-dimensional hybrid (kinetic ions and massless fluid electrons) simulations of the Kelvin-Helmholtz instability (KHI) for a magnetopause configuration with a varying density jump and magnetic shear across the boundary are carried out to examine how the transport of magnetosheath plasma into the magnetosphere is affected by these conditions. Low magnetic shear conditions where the magnetosheath magnetic field is within 30° of northward is included in the simulations because KHI is thought to be important for plasma transport only for northward or near-northward interplanetary magnetic field orientations. The simulations show that coherent vortices can grow for these near-northward angles and that they are sometimes more coherent than for pure northward conditions because the turbulence which breaks down these vortices is reduced when there are magnetic tension forces. With increasing magnetic shear angle and increasing density jump, the growth rate is reduced, and the vortices do not grow to as large of a size, which reduces the plasma transport. By tracking the individual particle motions, diffusion coefficients can be obtained for the system, where the diffusion is not classical in nature but instead has a time dependence resulting from both the increasingly large-scale vortex motion and the small-scale turbulence generated in the breakdown of the instabilities. Results indicate that diffusion on the order of 109 m2/s could possibly be generated by KHI on the flanks of the magnetosphere.

Research paper thumbnail of Ion heating and energy partition at the heliospheric termination shock: hybrid simulations and analytical model

Journal of Geophysical Research Atmospheres, 2009

ABSTRACT

Research paper thumbnail of Kinetic physics of the mirror instability

Journal of Geophysical Research, 1993

Kinetic mechanisms for the growth and saturation of the mirror instability are described using on... more Kinetic mechanisms for the growth and saturation of the mirror instability are described using one-dimensional hybrid simulations. Two parameter regimes are considered. In the first regime, a relatively small ion anisotropy excites a slowly growing instability that produces small-amplitude waves; most ions respond to the waves as an adiabatic fluid. In the second regime a large anisotropy excites a rapidly growing instability that generates large-amplitude waves; the response of many ions in this case is nonadiabatic. The difference in ion response is due to the relative importance of two ion populations, resonant and nonresonant. Resonant ions, those ions with low velocities parallel to the background magnetic field, contribute to the growth of the instability as a result of their gyrointeractions with the noncoplanar component of the waves electric field and respond to the mirror waves nonadiabatically. Nonreasonant ions, those with large parallel velocities, respond as an adiabatic fluid. In both regimes, ion anisotropy is reduced by means of the magnetic mirror force; in the second regime, the anisotropy reduction reduces the free energy available for wave growth and leads to the saturation of the mirror instability.

Research paper thumbnail of Alfv�n-cyclotron scattering of solar wind ions: Hybrid simulations

Journal of Geophysical Research, 2006