Dynamic fluid kinetic (DyFK) simulation of auroral ion transport: Synergistic effects of parallel potentials, transverse ion heating, and soft electron precipitation

Abstract

[1] Ion outflow processes along auroral field lines are simulated with a dynamic fluid kinetic (DyFK) model which couples a comprehensive fluid ionospheric (120-1100 km altitude) model to a semikinetic treatment for the topside through 3 R E region. Using a simplified electron description, large-scale extended parallel electrical fields driven by anisotropic hot plasma distributions have been incorporated in addition to the soft auroral electron precipitation and wave-driven ion-heating processes previously simulated [Wu et al., 1999]. Simulations show that auroral ionospheric ion outflows involve initial evacuation, ion-heating, and replenishment phases. The ionospheric ion supply is effectively elevated by the soft electron precipitation to topside altitudes, where the wave-driven transverse ion heating pumps ions upward. The altitude distribution and duration of wave heating and potential drop largely affect the ''pressure cooker'' ion trap formation. With comparable and persistent downward potential drop and wave heating, the pressure cooker produces slow and dense suprathermal ion outflows. The ion velocity distribution evolves in an extended ion trap from bowl and counterstreaming suprathermal conic distributions at lower altitudes into mirrored conics and finally toroidal distributions at the top of the pressure cooker. The wave heating is less effective for H + ions, owing partly to their fast transit through the wave-heating region. The H + ion trap tends to be lower but more extended in altitudinal extent than the O + ion trap. H + flux and total flow are about a third to half of those of O + . Some of the toroidal distributions and ion species variations of beam and conic energies in these simulations qualitatively resemble satellite observations of such ion distributions.

Global aspects of solar wind–ionosphere interactions

“…An additional relationship (Strangeway, private communication, 2005) was used to specify the ionospheric O + temperature dependence on Poynting flux. Ion heating and electron heating are observed to produce independent outflows (Wahlund et al, 1992), and theoretical work reinforces this (Wu et al, 2002). However, the O + flux was specified as the geometric mean of the two scalings, because it is thought that some level of Poynting flux is essential to convert up-flow into out-flow.…”

Optical estimation of auroral ion upflow: 2. A case study

“…Spacecraft measurements from sounding rockets and satellites provide in situ observations of particle kinetics [ Kintner et al , 1996] and plasma waves [ André et al , 1998; Chaston et al , 2006]. While there is evidence that ion upflow and outflow are related [ Wu et al , 2002; Strangeway et al , 2005; Lynch et al , 2007] the exact relationship of these two phenomena is unclear. Combined ISR‐spacecraft data sets are needed to observe both the bulk upflow processes and energetic distributions of outflowing ions and resolve this problem.…”

Simulation of the formation of O+ density troughs at 6000 km altitude in the polar cap ionosphere‐magnetosphere region

“…The simulation results presented in this paper were obtained with the UT Arlington 1.5‐dimension time‐dependent Dynamic Fluid‐Kinetic (DyFK) model which simulates ionospheric plasma transport along a magnetic flux tube. This model is designed to simulate high‐latitude plasma transport dynamics [ Estep et al , 1999; Wu et al , 1999, 2002; Tu et al , 2004, 2005]. The DyFK model couples a truncated version of the moment based field line interhemispheric plasmasphere (FLIP) treatment [ Richards and Torr , 1990], typically for the region from 120 km to 1100 km altitude, to the generalized semikinetic (GSK) treatment [e.g., Wilson , 1992] of the higher‐altitude region, typically in the range from 800 km to 3–8 R E altitude.…”