Two-Dimensional Particle-in-Cell Simulation of Magnetosonic Wave Excitation in a Dipole Magnetic Field

Abstract

The excitation of magnetosonic waves in the meridian plane of a rescaled dipole magnetic field is investigated, for the first time, using a general curvilinear particle-in-cell simulation. Our simulation demonstrates that the magnetosonic waves are excited near the equatorial plane by tenuous ring distribution protons. The waves propagate nearly perpendicularly to the background magnetic field along both radially inward and outward directions. Different speeds of inward and outward propagation result in the asymmetrical distribution about the source region. The waves are accompanied by energization of both cool protons and electrons near the wave source region. The cool protons are heated perpendicularly, while the cool electrons can be heated in the parallel direction and also experience enhanced perpendicular drift at the presence of intense wave power. The implications of simulation results to the observations of magnetosonic waves and related particle heating in the inner magnetosphere are also discussed. Plain Language Summary The Earth's radiation belt is a natural space environment consisting of relativistic electrons trapped in geospace. It exhibits great variability due to solar activities and poses a great threat to spacecraft orbiting in the regions and to astronauts. The primary physical process involved for radiation belt variability is through interaction with electromagnetic waves. Magnetosonic waves are one of the important waves that are capable of electron scattering, the efficiency of which depends on the wave detailed properties. Previous simulation has investigated the wave excitation in a homogeneous plasma. Here we present for the first time a 2-D particle-in-cell simulation to understand magnetosonic wave excitation and propagation in an inhomogeneous dipole magnetic field. The simulation results not only illustrate the wave temporal evolution and spatial distribution, both in radial and latitudinal distribution, but also reveal their effects on thermal electron and proton heating. These results are ready for verification against wave and particle measurement from the ongoing magnetospheric missions such as Van Allen Probes.