Parallel electric fields in nonlinear magnetosonic waves

Abstract

The electric field parallel to the magnetic field, E‖, in nonlinear magnetosonic waves is studied theoretically and numerically. In the calculation of E‖ based on the conventional reductive perturbation method, the terms related to the magnetic pressure cancel, and E‖ is proportional to the electron temperature Te. With a modified perturbation scheme assuming that the wave amplitude is in the range (me∕mi)1∕2<ϵ<1, an expression for E‖ is obtained that is proportional to the magnetic pressure in a cold plasma. Its integral along the magnetic field, F=−∫E‖ds, is proportional to ϵ2mivA2. One-dimensional, fully kinetic, electromagnetic particle simulations verify the theoretical predictions for small-amplitude waves. Further, they demonstrate that eF becomes of the order of ϵ(mivA2+ΓeTe) in large-amplitude [ϵ∼O(1)] oblique shock waves. These theory and simulations indicate that E‖ in magnetosonic waves can be strong in a strong magnetic field.