Preliminary Simulation Analysis Of Earth Magnetosphere Magnetic Reconnection Process And Mechanism

Magnetic field activity is the basis of many transient phenomena in the universe such as the flares of the sun and stars,sub-explosions of magnetosphere,and gamma-ray bursts.The magnetic field energy that triggers these processes may be released by magnetic reconnection.The occurrence of magnetic reconnection changes the topology of the magnetic field and converts the magnetic field energy into plasma energy.In this paper,the 2.5D PIC?particle-in-cell?method is used to simulate the collisionless magnetic reconnection without the guide field and the collisionless magnetic reconnection with the guide field.We have made the following conclusions on the specific analysis of the field magnetic reconnection without guide field and the reconnection with field,including the reconnection magnetic field,the electron current,the ion current,the electron velocity and the ion velocity with the guided field magnetic reconnection:An dipolarization fronts structure is formed during the reconnection process.In the dipolarization fronts structure,B_yis symmetric along the X point,and B_zexhibits a quadrupole structure with a maximum intensity of 0.18B₀,where the propagation velocity of B_zis super-Alfvén velocity.The electron current density and the ion current density are not the same during the reconnection process.The electron current is small near the X point but mainly distributed throughout the magnetic island region.The ion current is mainly symmetrically distributed around the X point.The electron current density is greater than the ion current density during the reconnection process.The density of ions near the X and X separation lines is very small,mainly distributed in the magnetic island.But the electrons are mainly distributed in the area near the X point outside the magnetic island,and have a increased area with width about 0.2d_inear the X point.The outflow region and the inflow region of the ion are all within the ion inertia scale,while the electron outflow and inflow regions are mainly distributed in the electron inertia scale,and the electron outflow velocity is super-Alfvén speed and the ion outflow velocity slightly smaller than Alfvén velocity.When a strong guiding field exists,the reconnection rate decreases as the guiding field increases.In the fast reconnection phase,the reconnection electric field E_zis mainly provided by off-diagonal terms of the electron pressure and the electron motion terms.The quadrupole distribution of B_zand the symmetric structure of B_ygenerated by magnetic reconnection are destroyed in the presence of the guiding field.The distribution of the positive direction of B_zoccupies almost entire magnetic island portion and has a narrow area in the X point region.The strip distribution,while the B_znegative direction has a break near the X point.It is different with the reconnection without the guide field B_z0=B₀,when there is a guide field B_z0=B₀the distribution of electron density and ion density is very similar.By analyzing particle density and particle velocity,we know that electrons and ions are mainly accelerated near the X separation line when there is a guiding field B_z0=B₀.