Numerical Simulation Of Dynamic Process Of Energy Conversion In The Earth Magnetosphere

Plasma is the fourth state of matter,in addition to solid,liquid,and gas,and constitutes 99%of the matter in the universe.As the most abundant state of matter in the universe,the study of plasma under extreme conditions(such as high temperature,high pressure,strong radiation,low temperature,low pressure,etc.)is of great significance for unraveling the mysteries of the universe,understanding the interaction mechanisms between the Sun and Earth,and advancing the development of space exploration and materials science.The Sun-Earth space,as the only natural laboratory of plasma observable and perceptible by humans,has become a key region for understanding the physical properties of plasma and extreme space weather phenomena.The extreme space environment of the Sun-Earth system is influenced by energy conversion processes such as solar flares,coronal mass ejections,magnetic storms,substorms,etc.,which also play important roles in the dynamics of the magnetosphere.The Earth’s magnetosphere is one of the natural laboratories for studying plasma in the Sun-Earth space and is often used to study energy conversion in plasma,mainly including the conversion between electromagnetic field energy and particle kinetic and thermal energy.Collisionless magnetic reconnection,as a fundamental plasma physics process,involves changes in magnetic field topology,rapidly converting magnetic energy into plasma kinetic and thermal energy.It is considered a primary cause of numerous high-energy eruptive events in space and one of the main mechanisms for the input of solar wind energy into the magnetosphere and the generation of high-energy particles in the magnetosphere.The triggering mechanism of magnetic reconnection,the distribution of energy conversion,the mechanism of particle acceleration and heating,and the coupling of multi-scale,multi-region dynamics in the magnetosphere are long-standing unresolved fundamental issues and forefront challenges of close attention.In this paper,addressing the unresolved issues concerning energy conversion distribution in reconnection and multi-scale,multi-region coupling in the magnetosphere,we employ 2.5D particle-in-cell simulations and 3D global-scale hybrid simulations to investigate the dynamic processes of energy conversion in the magnetosphere,obtaining the following results:1.The energy conversion dynamics processes during symmetric magnetic reconnection are systematically studied.We found that the energy conversion mainly occurs in the reconnection fronts and magnetic islands where the flux piles up.The energy conversion rate decreases with the increase of plasma density and guiding field.The island coalescence process enhances the energy conversion in magnetic islands.In the K-H turbulence driven by reconnection,ions gain energy through the non-ideal electric field (?),while electrons lose energy to drive the K-H instability.The interaction between electron vortices and secondary reconnection promotes the non-ideal energy conversion in the turbulent region.2.The electromagnetic fields near the diffusion region of symmetric reconnection are studied,confirming the existence of the Larmor electric field in symmetric reconnection.The Lamor electric field is a transient structure upstream of the Hall electric field in symmetric reconnection which only exists in the stage of rapid increase of reconnection rate.According to the generalized Ohm’s law,the Larmor electric field is produced by the thinning of the current sheet and gradually disappears by the thickening of the current sheet.From the dynamic point of view,the Larmor electric field is generated by the Larmor radius effect of high-energy ions and disappears by the empties of high-energy ions.The Larmor electric field amplitude decreases with the increase of the half-width of the initial current sheet and the background plasma density.With the increase of guide field,background temperature,and ion-electron mass ratio,the amplitude of the Larmor electric field increases.3.Electron-only reconnection during island coalescence is reproduced.We find that electron-only reconnection is the early stage of merging reconnection and the degree of ion coupling is insensitive to the length of the current sheet.Electron-only reconnection does not mean that ions do not participate in the reconnection,it is also affected by the reconnection electric field.The ion outflow can be suppressed by the pre-existing background current and Hall electric field E_z.4.The dynamical processes related to dayside magnetopause reconnection are studied,revealing that the locations of the magnetopause reconnection depend not only on the initial IMF direction but also on the local dynamic processes of the magnetopause,such as the generation,transport,and coalescence of the flux rope,the reconnection within the flux rope,the reconnection at low latitude,and magnetic sheath flow.The energy transport from the magnetopause surface to the magnetosphere is mainly in the form of plasma energy.A large part of solar wind energy does not enter the magnetosphere directly but is transported from low latitude to high latitude in the magnetopause current layer with reconnection outflow and flux rope,and from the subsolar point region to the tail magnetopause with the magnetopause drift flow.The research findings of this paper reveal the distribution of energy conversion in magnetic reconnection and its correlation with the upstream plasma environment,demonstrating the presence of the Larmor electric field in symmetric magnetic reconnection.From the perspective of ion dynamics,a new interpretation for electron-only reconnection is proposed,elucidating the dependence of magnetopause reconnection and energy transport on magnetopause dynamics and solar wind conditions.This further deepens our understanding of the dynamics of energy conversion in the Earth’s magnetosphere,facilitating comprehension of particle dynamics processes within plasmas and the energy conversion processes between charged particles and electromagnetic fields.This research contributes significantly to deepening our understanding of space environments and eruptive phenomena,as well as advancing our knowledge of the origin and acceleration of the solar corona and solar wind.Consequently,it holds significant scientific importance and offers broad application prospects for advancing future research in deep space exploration.