With the measurements of magnetic field of Venus Express (VEX), magnetic coplanarity and minimum variance analysis (MVA) methods are analyzed and their validity is tested to determine the normal of Venusian bow shocks. It is found that MVA method is the better than magnetic coplanarity, and 95% shock crossings can be accurately determined by the method. However, the occurrence of the shock normal which is not determined accurately by magnetic coplanarity increases with the decrease of the solar zenith angle (SZA). At the same time, compared with quasi-parallel shocks, there is more occurrence of the shock normal which cannot be determined accurately by magnetic coplanarity for quasi-perpendicular shocks.
The evolution of two-dimensional（2D） electron phase-space holes（electron holes） has been previously investigated with electrostatic Particle-in-Cell（PIC） simulations,which neglect ion dynamics.The electron holes are found to be unstable to the transverse instability,and their evolution is determined by the combined action between the transverse instability and the stabilization by the background magnetic field.In this paper,the effect of ion dynamics on the evolution of an electron hole is studied.In weakly magnetized plasma(Ωe<ωpe,whereΩe andωpe are electron gyrofrequency and plasma frequency,respectively),the electron hole is still unstable to the transverse instability. However,it evolves a little faster and is destroyed in a shorter time when ion dynamics is considered. In strongly magnetized plasma(Ωe>ωpe),the electron hole is broken due to the lower hybrid waves, and its evolution is much faster.
