Cao Jin-Bin

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.

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 less 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.

Is the Near-Earth Current Sheet Prior to Reconnection Unstable to Tearing Mode?

The tearing mode instability plays a key role in the triggering process of reconnection. The triggering collisionless tearing mode instability has been theoretically and numerically analyzed by many researchers. However, due to the difficulty in obtaining the observational wave number, it is still unknown whether the tearing mode instability can be excited in an actual plasma sheet prior to reconnection onset. Using the data from four Cluster satellites prior to a magnetospheric reconnection event on 13 September 2002, we utilized the wave telescope technique to obtain the wave number which corresponds to the peak of power spectral density. The wavelength is about 18RE and is consistent with previous theoretic and numerical results. After substituting the wave vector and other necessary parameters of the observed current sheet into the triggering condition of tearing mode instability, we find that the near-Earth current sheet prior to reconnection is unstable to tearing mode.

Ionospheric Feedback Instability in the Coupling of Magnetosphere-Ionosphere

The ionospheric feedback instability is discussed by using the conductivity argument. We give an exact quantitative description to show that the free energy for this instability comes from the reduction of the Joule dissipation produced by the pre-existing convection electric field through self-consistent changes in ionization and conductivity due to Alfvenic perturbations in the ionosphere. By the over-reflection of Alfven waves, the energy in the active ionosphere is pumped into the magnetosphere, which is contrary to the usual case whereby energy carried by Alfven waves is deposited in the ionosphere by Joule dissipation. The ionospheric feedback enhances the electron E×B drift. The electron conductivity is controlled by the ion Perdersen conductivity rather than by the electrons Pedersen conductivity. We also provide a qualitative theoretical explanation to the intense aurora favoured by a lower ambient ionospheric conductivity in the ionospheric feedback instability.

Dipole Alfven Vortex 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.

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.