Difference Between the Ion Gyroviscous Effect and Hall Magnetohydrodynamic Effect in the Magnetic Reconnection

We study the ion gyroviscous effect and Hall magnetohydrodynamic (MHD) effect separately using the modified MHD simulation of the magnetopause. Simulations show that the ion gyroviscous effect is on the order of a characteristic scale of ion Larmor radius and is mainly limited near the magnetosheath boundary. The Hall MHD effect is on the order of a characteristic scale of ion inertial length and occurs mainly in the central region of the current layer. The magnetic field component out of the simulation plane has a bipolar structure near the magnetosheath boundary from the ion gyroviscous effect and a quadrupole structure in the central region of the current layer from the Hall MHD effect. These results are of fundamental importance in understanding the reconnection processes in space and astrophysical plasma.

Modified Magnetohydrodynamic Model of Magnetic Reconnection

This paper presents the modified magnetohydrodynamic(MHD)model and simulations of solar wind-magnetosphere interactions.We use the two-dimensional and three-component,compressible,resistive,ion gyroviscous and Hall MHD model,i.e.,including the ion Unite Larmor radius(FLR)and Hall MHD effects,but neglecting the electron inertia and electron FLR effects.The composed dynamic pressure pulses(shear variations in the How velocity)in the solar wind form gusts that continually buffet the magnetosphere and cause the time-dependent magnetic reconnection at the magnetopause.The results show that the magnetic Held and the How velocity components perpendicular to the reconnection plane can be generated in magnetopause current layer.The vortical How structures can also occur in the magnetospheric side region.These results are responsible for non-ideal MHD properties of the plasma fluid,i.e.,ion FLR and Hall MHD effects.

Micro Perpendicular Pickup Process of Newborn Ions

The micro perpendicular pickup process of newborn ions is considered by means of one-dimensional electromagnetic hybrid computer simulations of homogeneous plasmas. It is found that there exists the micro perpendicular pickup process for newborn ions. The phase angle diffusion time is Jess than (not larger than) the time for pitch-angle scattering to a relatively thin shell and much faster than the energy scattering time for broadening of the shell toward a thermal distribution.

Influence of the Nongyrotropy on the Gyrotropic Ring Instability

The instability driven by the nongyrotropic newborn ions is studied for oblique propagation.The results show the influence of nongyrotropic on the gyrotropic ring instability decreases when the propagation angle increases.The growth rate in the case of nongyrotropic is smaller than that in the case of gyrotropic.The nongyrotropic also breaks the symmetry of the propagation of the waves in the plane perpendicular to the ambient magnetic field.

Particle Simulations for Electron Beam-Plasma Interactions

The computer simulations of high-frequency instabilities excited by the high density electron beam and their nonlinear effect are presented.One-dimensional electromagnetic particle simulations are performed with different values of the electron beam-to-plasma density ratio.The results show that for the high electron beam-to-background plasma density ratio,all the Langmuir waves and two electromagnetic waves with left-hand and right-hand circular polarizations(i.e.,the“L-O mode”and the“R-X mode”)propagating parallel to the magnetic field can be generated and the maximum values of wave electric fields are nearly the same.The electron beam and background plasma are diffused and a part of energetic background electrons are obviously accelerated by the wave-particle interactions.The heating of the beam and background plasma is mainly due to the electrostatic(Langmuir)wave-particle interactions,but the accelerations of a part of energetic background electrons may be mainly due to the electromagnetic wave-particle interactions.

Dipole AlfvenVortex with Finite Ion Larmor Radius in a Low-Beta Plasma

A set of nonlinear fluid equations which include the effects of ion gyroradius is derived to describe Alfven vortex. The correction of finite ion gyroradius to the Alfven vortex in the inertial region is much more significant than that in the kinetic region. The amplitude of the vortex is enhanced in both regions. The scale of the vortex in the kinetic region becomes larger whereas it becomes smaller in the inertial region.