Simulating Chorus Waves in a Dipole Magnetic Field

One- and two-dimensional electromagnetic particle-in-cell simulations are performed to simulate the excitation of chorus waves with discrete rising-tone elements in a dipole magnetic field. Previous chorus simulations often resorted to scaled-down systems with the spatial inhomogeneity of the background magnetic field much larger than realistic values in the magnetosphere to reduce computation time. In contrast, one-dimensional simulations in both scaled-down and full-scale dipole magnetic fields are carried out in the present study. The results demonstrate that the generation of discrete chorus elements depends on various plasma parameters, including the concentration and temperature anisotropy of the suprathermal electrons driving the wave growth and the spatial inhomogeneity of the background magnetic field which is effectively controlled by the scale of the dipole magnetic field used. Two-dimensional simulation results in a scaled-down dipole magnetic field are also presented to investigate how the wave excitation changes when obliquely-propagating waves become possible.