Particle simulations of driven collisionless magnetic reconnection at the dayside magnetopause

Abstract

Basic plasma processes associated with driven collisionless magnetic reconnection at the Earth's dayside magnetopause are studied on the basis of particle simulations. A two‐and‐one‐half‐dimensional (2½‐D) electromagnetic particle simulation model with a driven inflow boundary and an open outflow boundary is developed for the present study. The driven inflow boundary is featured with a driving electric field for the vector potential, while the open outflow boundary is characterized by a vacuum force‐free condition for the electrostatic potential. The major findings are as follows: (1) the simulations exhibit both quasi‐steady single X line reconnection and intermittent multiple X line reconnection (MXR); the MXR process is characterized by repeated formation and convection of magnetic islands; (2) particle acceleration in the reconnection process results in a power law energy spectrum of ƒ(E) ∼ E−4 for energetic ions with E > 40 keV and energetic electrons with E > 3 keV, where E is the particle energy; particles are accelerated to high energy near magnetic O line regions as particles are trapped within magnetic islands; (3) field‐aligned particle heat fluxes and intense plasma waves associated with the collisionless magnetic reconnection process are also observed; typical power spectra of fluctuating magnetic and electric fields are found to be PB ∼ f−3.6 and PE ∼ f−1.8, respectively, where f is the wave frequency; (4) when applied to the dayside magnetopause, simulation results show that the MXR process tends to generate a simultaneous magnetic field perturbation on both sides of the dayside magnetopause, resembling the observed features of two‐regime flux transfer events (FTEs); and (5) an intrusion of magnetosheath plasma bulge into the magnetosphere due to the formation of magnetic islands may lead to the layered structures observed in magnetospheric FTEs. Simulation results are applied to the dayside magnetopause to provide an explanation for some features associated with dayside magnetic reconnection and FTEs.