Monte Carlo study of the transition region in the polar wind: An improved collision model

Journal Article · Fri Oct 01 04:00:00 EDT 1993 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JA01190· OSTI ID:75640

Barghouthi, I A; Barakat, A R; Schunk, R W ^[1]

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1. Utah State Univ., Logan, UT (United States)

A Monte Carlo simulation was used to study the steady state flow of the polar wind protons through a background of O{sup +} ions. The simulation region included a collision-dominated region (barosphere), a collisionless region (exosphere), and the transition layer embedded between these two regions. Special attention was given to using an accurate collision model, i.e., the Fokker-Planck expression was used to represent H{sup +} - O{sup +} collisions. The model also included the effects of gravity, the polarization electric field, and the divergence of the geomagnetic field. For each simulation, 10{sup 5} particles were monitored, and the collected data were used to calculate the H{sup +} velocity distribution function f{sub H+}, density, drift velocity, parallel and perpendicular temperatures, and heat fluxes for parallel and perpendicular energies at different altitudes. The transition region plays a pivotal role in the behavior of the H{sup +} flow. First, the shape of the distribution function is very close to a slowly drifting Maxwellian in the barosphere, while a `kidney bean` shape prevails in the exosphere. Second, the flow changes from subsonic (in the barosphere) to supersonic (in the exosphere) within the transition region. Third, the H{sup +} parallel and perpendicular temperatures increase with altitude in the barosphere due to frictional heating, while they decrease with altitude in the exosphere due to adiabatic cooling. Fourth, the heat fluxes of the parallel and perpendicular energies are positive and increase with altitude in the barosphere, and they change rapidly from their maximum values to their minimum values within the transition region. It was found that the choice of the collision model can alter the results significantly. Both the body forces and collision model have a large effect on the heat flux, while they have only a small quantitative effect on the lower-order moments (density, drift velocity, and temperature). 28 refs., 8 figs.

• Sponsoring Organization: USDOE
• OSTI ID: 75640
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A10 Vol. 98; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
IONOSPHERE
MONTE CARLO METHOD
OXYGEN IONS
POLAR REGIONS
PROTON TRANSPORT
SIMULATION
WIND