Effects of wave–particle interactions on the dynamic behavior of the generalized polar wind

Abstract

The effects of wave–particle interactions (WPI) on the plasma outflows at high latitudes was the subject of several studies. Previous attempts to address this problem, for the most part, modeled the response of the plasma on a “stationary” field line to certain pre-specified boundary conditions. However, the horizontal plasma drift across the different regions at high latitudes (i.e., the cusp, the polar cap, the nightside aurora, and the subauroral regions) results both in rapid changes in conditions and in a coupling of the different regions. Here, we used a time-dependent macroscopic particle-in-cell (mac-PIC) model to investigate the dynamic behavior of the “generalized” polar wind with horizontal plasma convection taken into account. A representative magnetic flux tube, extending from 2000 km to ∼8 R E , was followed as it crossed the different high latitude regions. The lower boundary conditions were adopted from a 3-D time-dependent hydrodynamic model, while the WPI levels were adopted from observations. The behavior of the generalized polar wind both with and without the WPI, and with and without the presence of magnetospheric electrons was investigated. The comparison of the results for these four cases elucidated the effects of WPI, and their relative importance with respect to those of the magnetospheric electrons. It was found that the WPI influence is more pronounced on the ion temperature, and progressively less apparent on the vertical drift, u(H +), and the density, n(H +), respectively. Also, the effect of the WPI was strongest in the cusp region. In contrast, the presence of magnetospheric electrons was the dominant factor for the evolution of n(H +) and u(H +) in the polar cap. It was also found that the n(H +) and u(H +) rates of change during the transition from the subauroral to the cusp regions were higher than the rates of change during the transition from the cusp to the polar cap.