AniaraCentrifugal acceleration at high altitudes above the polar cap: A Monte Carlo study
Al Quds University
A direct simulation Monte Carlo method is used to study the outflow of O+ and H+ ions along geomagnetic flux tubes at geocentric distances from about 1.2 Re to 15 Re above the polar cap. This is an extension of the Barghouthi model in which the effect of centrifugal acceleration is included. In addition,the magnetic field and fight trajectories, namely the central polar cap (CPC),
nightside polar cap (NPC) and cusp, were calculated using the Tsyganenko T96 model. The effect of centrifugal acceleration was simulated by considering three values for the ionospheric electric field: 0 (no centrifugal acceleration), 50, and 100 mV/m.
It was found that the centrifugal acceleration increases the parallel bulk velocity and decreases the parallel and perpendicular temperatures of both ion species at altitudes above about 4 Re. Centrifugal acceleration also increases the temperature anisotropy
at high altitudes. At a given altitude, centrifugal acceleration decreases the density of H+ ions while it increases the density
of O+ ions. This implies that with higher centrifugal acceleration more O+ ions overcome the potential barrier. It was also found that aside from two exceptions centrifugal acceleration has the same effect on the velocities of both ions. This implies that the centrifugal acceleration is universal for all particles. The parallel bulk velocities at a given value of ionospheric electric
field were highest in the cusp followed by the CPC followed by the NPC. In this study a region of no wave-particle interaction was assumed in the CPC and NPC between 3.7 and 7.5 Re. In this region the perpendicular temperature was found to decrease with altitude due to perpendicular adiabatic cooling.
Created 2015-06-04 14:41:04 by Mats HolmströmLast changed 2015-06-15 22:34:44 by Mats Holmström