The Effects of Altitude-Dependent Wave Particle Interactions on the Polar Wind Plasma
Source: Astrophysics and Space Science, Volume 259, Number 2, 1998 , pp. 117-140(24)
The energization of charged particles, due to interaction with the ambient electromagnetic turbulence, has a significant influence on the plasma transport in space. The effect of wave-particle interactions on the outflow characteristics of polar wind plasma was investigated. The theoretical model included gravitational acceleration (g), polarization electrostatic field (Ep), and divergence of the geomagnetic field. Within the simulation region (1.7 to 10 earth radii, Re) the ions were assume to be collisionless and the electrons to obey a Boltzmann relation. Profiles of altitude-dependent diffusion coefficients [D (O+) and D (H+)] were computed from the wave spectral density (S) observed by the Plasma Wave Instrument (PWI) on board DE-1. The effects of WPI were introduced via a Monte Carlo technique, and an iterative approach was used in order to converge to self-consistent results. The main conclusions of this study were the following. As a result of perpendicular heating, the temperature anisotropy (T| /T) was reduced and even reversed (T| < T) at high altitudes. The O+ velocity distribution function developed a conic shape at high altitudes. The altitudes above which the WPI influences the O+ ions were lower than those for the H+ ions. The escape flux of O+ could be enhanced by more than an order of magnitude while the H+ flux remains constant. The O+ ions are heated more efficiently than the H+ ions, especially at low altitudes due to the `pressure cooker' effect. As the ions are heated and move to higher altitudes, the ion's Larmor radius a_L may become comparable to the perpendicular wavelength . As the ratio aL / becomes > 1, the heating rate becomes self-limited and the ion distribution displays toroidal features. This result is consistent with the observation of O+ toroidal distribution in the high altitude ionosphere. Finally, the large variability in the wave spectral density S was studied. This variability was found to change our results only in a quantitative manner, while our conclusions remained qualitatively unchanged.
Document Type: Regular paper
Publication date: 1998-01-01