Jintao Cao

Joint observations by Cluster satellites of bursty bulk flows in the magnetotail

[1] Using the observations of three satellites of Cluster (C1, C3, and C4) during the periods July to October 2001 and July to October 2002, we study 209 active time bursty bulk flows (BBFs), the difference between single satellite observations and multisatellite observations, and the difference among three selection criteria (two about BBFs and one about rapid convection event). Single satellite observations show that the average duration of BBFs selected by the criterion of Angelopoulos et al. is 604 s, while multisatellite observations show that the average duration of BBFs is 1105 s. Single satellite sometimes misses the BBFs. The missing ratio of single satellite is 22.4% for the criterion of Angelopoulos et al. and 44.9 % for the criterion of Raj et al. Therefore the single satellite observations cannot tell the true number of BBFs. The multisatellite observations are more important for the criterion of Raj et al. The single satellite observations also show that 22% of substorms are not accompanied by BBFs, while multisatellite observations show that only 4.5% of substorms are not accompanied by BBFs. Thus it seems possible that all substorms are accompanied by BBFs. The occurrence frequency of RCEs in the central plasma sheet obtained by multisatellites is 12.2%. The occurrence frequency of BBFs in the central plasma sheet is 9.5% for single satellite observations and 19.4% for multisatellite observations. So BBFs may contribute more to the transport of magnetic flux, mass, and energy than what was estimated by previous studies based on single satellite observations.

Occurrence of reconnection jets at the dayside magnetopause: Double Star observations

We present a statistical study on reconnection occurrence at the dayside magnetopause performed using the Double Star TC1 plasma and magnetic field data. We examined the magnetopause crossings that occurred during the first year of the mission in the 0600 1800 LT interval and we identified plasma flows, at the magnetopause or in the boundary layer, with a different velocity with respect to the adjacent magnetosheath. We used the Walen relation to test which of these flows could be generated by magnetic reconnection. For some event we observed opposite-directed reconnection jets, which could be associated with the passage of the X-line near the satellite. We analyzed the occurrence of the reconnection jets and reconnection jet reversals in relation to the magnetosheath parameters, in particular the local Alfven Mach number, the plasma beta, and the magnetic shear angle. We also studied the positions and velocities of the reconnection jets and jet reversals in relation to the magnetosheath magnetic field clock angle. We found that the observations indicate the presence of a reconnection line hinged near the subsolar point and tilted according to the observed magnetosheath clock angle, consistently with the component merging model.

Quantum effects on Rayleigh–Taylor instability in magnetized plasma

The effects of the quantum mechanism and magnetic field on Rayleigh–Taylor (RT) instability in an ideal incompressible plasma are investigated. The explicit expression of the linear growth rate is obtained in the presence of fixed boundary conditions. It is shown that the magnetic field has a stabilizing effect on RT instability similar to the behavior in classical plasmas and RT instability is affected significantly by quantum effects. Quantum effects are also shown to suppress RT instability with the appropriate physical quantities. Some astrophysical parameters are discussed as an example to investigate the new effects.

Jeans instability in quantum magnetoplasma with resistive effects

The Jeans instability in dense quantum plasmas is investigated in the presence of two dimensional magnetic fields and resistive effects. The resistive effects are shown to introduce instability whether the perturbation is stable or not in the ideal magnetohydrodynamic model. The analytical expressions of the growth rate of Jeans instability are obtained for both the finite and remarkable resistive effects cases. The results are relevant to dense astrophysical objects, e.g., neutron stars and the interior of white dwarfs, as well as low-temperature laboratory plasmas.

Larmor radius size density holes discovered in the solar wind upstream of Earth’s bow shock

The Cluster and Double Star satellites recently observed plasma density holes upstream of Earth’s collisionless bow shock to apogee distances of ∼19 and 13 earth radii, respectively. A survey of 147 isolated density holes using 4s time resolution data shows they have a mean duration of ∼17.9±10.4s, but holes as short as 4s are observed. The average fractional density depletion (δn∕n) inside the holes is ∼0.68±0.14. The upstream edge of density holes can have enhanced densities that are five or more times the solar wind density. Particle distributions show the steepened edge can behave like a shock. Multispacecraft analyses show the density holes move with the solar wind, can have an ion gyroradius scale, and could be expanding. A small normal electric field points outward. Similarly shaped magnetic holes accompany the density holes indicating strong coupling between fields and particles. The density holes are only observed with upstream particles, suggesting that backstreaming particles interacting with t...

Electrostatic drift modes in quantum dusty plasmas with Jeans terms

Electrostatic drift waves (EDWs) are investigated in nonuniform quantum magnetized dusty plasmas by taking into account dust gravitational effects with the help of the quantum hydrodynamic model. Ions and electrons are viewed as low-temperature Fermi gases, whereas quantum effects are neglected for the dust grains. The analytical dispersion relationship of the quantum EDWs is derived. Quantum effects are shown to affect the dispersion of EDW significantly. The Jeans terms induce a driftlike instability, which does not exist with the absence of gravitational effects. The criteria and growth rate of the kind of instability are presented. Our results are relevant to dense astrophysical objects such as the interiors of astrophysical compact objects (e.g., white dwarfs and neutron stars).

The effect of the Hall term on Jeans instability in quantum magnetoplasma with resistive effects

The Jeans instability in dense quantum plasmas is investigated by taking into account the Hall term and resistivity in the presence of two-dimensional magnetic fields. The general dispersion relation is presented. The presence of the Hall term introduces a new wave mode which does not exist in the ideal magnetohydrodynamic framework. Two limiting cases with respect to the Hall effect are discussed. The Hall effect is shown to induce a frequency shift but does not change the instability criterion. The resistivity exhibits damping or destabilizing effects on the plasma system under different circumstances. The analytical expressions of the growth/damping rate of Jeans instability are obtained for both the finite and remarkable resistivity cases in the absence of the Hall term.

Behavior of current sheets at directional magnetic discontinuities in the solar wind at 0.72 AU

[1] Venus Express interplanetary magnetic field measurements have been examined for magnetic ‘‘holes,’’ accompanied by magnetic field directional changes. We examine both the thickness of the current sheet and the depth of the magnetic field depression. We find the thickness of the current sheet is not correlated with the depth of the field depression. The depth of the magnetic holes is related to directional angle change. Since total pressure should balance across these discontinuities, there must be enhanced plasma pressure within the magnetic holes. The dependence of the depth of the hole (i.e., size of the plasma pressure enhancement) on the directional changes suggests that the heating of the plasma associated with the hole formation may be provided by annihilation of the magnetic energy in the current sheet, via slow reconnection. Citation: Zhang, T. L., et al. (2008), Behavior of current sheets at directional magnetic discontinuities in the solar wind at 0.72 AU, Geophys. Res. Lett., 35, L24102, doi:10.1029/2008GL036120.

Effects of shear flow and transverse magnetic field on Richtmyer–Meshkov instability

The effects of shear flow and transverse magnetic field on Richtmyer–Meshkov instability are examined and the expression of the interface perturbation is obtained by analytically solving the linear ideal magnetohydrodynamics equations. It shows that the perturbation evolves exponentially rather than linearly in the presence of shear flow and magnetic field when va<1−AT2δu∕2, where va is the modified Alfven velocity, AT is the Atwood number, and δu is the relative shear velocity, respectively. The shear flow acts as a destabilizing source, while the magnetic field is a stabilizing mechanism of the shocked corrugated interface problem. The whole analysis is based on the assumption that the fluid is incompressible.

Venus Express observations of an atypically distant bow shock during the passage of an interplanetary coronal mass ejection

[1] On 10-11 September 2006 the Venus Express magnetometer detected a very strong Interplanetary Coronal Mass Ejection (ICME) event with an average field about 2 times higher than that of a typical ICME at 0.72 AU. While the effective obstacle to the solar wind is compressed to a smaller dimension during this ICME event, the bow shock is located far upstream of its nominal location. The observed shocks are weak and appear very dynamic. The location of the shock crossing can be found all along the Venus Express trajectory, which has an apocenter of 12 R v . We attribute the atypical distant bow shock location as an effect of the extremely low Mach number during the ICME.