Effects of wave‐particle interactions on H+ and O+ outflow at high latitude: A comparative study

Abstract

A Monte Carlo simulation was used to study the effects of wave‐particle interactions (WPI) on ion outflow at high latitudes (the auroral region and the polar cap). As the ions drift upward along the geomagnetic field lines, they interact with the electromagnetic turbulence and, consequently, get heated in the direction perpendicular to the geomagnetic field. The mirror force converts some of the gained ion energy in the perpendicular direction into parallel kinetic energy. These effects combine to form an ion‐conic distribution. Previous studies of WPI in the auroral region neglected the body forces (i.e., gravitational and polarization electrostatic) and the altitude dependence of the spectral density. In contrast, this work includes the effect of body forces and an altitude‐dependent spectral density. The ion distribution function, the profiles of ion density, drift velocity, and parallel and perpendicular temperatures are presented for both H+ and O+ ions. These results are compared with the ones corresponding to polar wind conditions. The main conclusions are as follows: (1) the effect of body forces is more important in the polar wind case and for the O+ ions than it is for the auroral region and the H+ ions, respectively; (2) the O+ ions are preferentially energized in both regions; (3) both ions (H+ and O+) are more energetic in the auroral region at most altitudes; and (4) the results of the Monte Carlo simulations agree with the “analytical” results of the mean particle theory.