Magnetic Reconnection Simulated By Magnetohydrodynamics In Earth's Magnetosphere

There are many explosive phenomena in the plasma environment of the solar-terrestrial space,such as the evolution of solar flares,coronal mass ejection,and the interaction of solar winds with the Earth's magnetosphere,which are closely related to magnetic reconnection.Magnetic reconnection rearranges topological configuration of magnetic field,in which the magnetic energy is rapidly transformed into the kinetic energy and thermal energy of plasma.These studies play an extremely important role in the prevention of disastrous space weather.In this paper,the 2.5-dimensional two-fluid MHD numerical simulation is used for the Earth's magnetospheric plasma environment,in which the Hall effect term in the generalized Ohm's law is taken into consideration.The magnetic reconnection process in Earth's magnetosphere is preliminarily studied.The changes of various physical quantities over time are obtained:magnetic field configuration,electric field distribution,the spatial distribution of electron and ion flow,and we get the detailed understanding of the changes in the number density and velocity of electrons with spatial coordinates.The simulation results show that when the reconnection rate reaches the maximum,the number density of the ion flow in the inflowing direction exhibits a distribution which is high in the middle and low on both sides.The number density in the outflowing direction shows a distribution which is high on both sides and low in the middle.The High density areas are concentrated in the outflowing region,and the number density at the reconnection point is the lowest.The number density distribution of the electron in the inflowing direction is slightly different from the ion flow,and the number density distribution in the outflowing direction is similar to the ion flow.In the process of magnetic reconnection,the ion flow and electron flow are symmetrically distributed in the left and right outflowing regions.Most of the ions merge in the outflowing region forming a structure with a scale close to the ion inertial scale in the y direction,however,the electron flow is mainly distributed near the separator,and the electron flow forms a structure with a scale close to the electron inertial scale.In addition,the Hall current in the reconnection plane generates a Hall quadrupole magnetic field structure,the typical characteristic of magnetic reconnection considering the Hall effect,which is distributed near the separator.In the simulation of this paper,the maximum reconnection rate in the collisionless magnetic reconnection model considering the Hall effect is about 0.11,and the maximum of the quadrupole magnetic field at the maximal reconnection rate is about0.12B₀.The quadrupole magnetic field structure corresponds to the current configuration in the reconnection plane.