Seasonal and solar activity dependence of the generalized polar wind with low-altitude auroral ion energization

Details Seasonal and solar activity dependence of the generalized polar wind with low-altitude auroral ion energization Seasonal and solar activity dependence of the generalized polar wind with low-altitude auroral ion energization

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.1405b&link_type=abstract

Journal of Geophysical Research, Volume 108, Issue A11, pp. SIA 5-1, CiteID 1405, DOI 10.1029/2002JA009360

Other

5

Ionosphere: Polar Cap Ionosphere, Ionosphere: Ionosphere/Magnetosphere Interactions (2736), Ionosphere: Particle Acceleration, Ionosphere: Plasma Convection

Scientific paper

The effects of low-altitude energization (LAE) of ions on the dynamic behavior of the high-latitude plasma was investigated using a macroscopic particle-in-cell (mac-PIC) model. The model simulates the behavior of a plasma-filled flux tube as it drifts across the different high-latitude regions (cusp, polar cap, auroral, and subauroral regions). In addition to the LAE, the model properly accounts for gravity, electrostatic field, magnetic mirror force, ion-ion collisions, wave-particle interactions, magnetospheric electrons, and centrifugal acceleration. However, the focus here is on the effects of the LAE and their seasonal dependence. The LAE was emulated by uniform energization of the ions in the perpendicular direction as they pass through a narrow domain (200 km in altitude) that is embedded within the cusp/auroral oval region. The roles that season, solar activity, and the altitude of the LAE play, with regard to the effects of the LAE on the plasma characteristics, were studied. In particular, several simulation runs were performed for different seasons (summer/winter), for different solar activity levels, and for different altitudes of the LAE region. Comparing the results from these runs, the following conclusions can be drawn: (1) When the LAE occurs at high altitudes, where less O+ exists, it does not appreciably enhance the O+ escape flux. The O+ escape flux for LAE occurring above ~3000 km is almost identical to the case with no LAE. (2) In the absence of LAE, the dominant source of escaping O+ occurs in the polar cap due to magnetospheric electrons. (3) Both upward and downward O+ fluxes occur at low altitudes, while only upward O+ fluxes occur at high altitudes. (4) As the plasma drifts from the polar cap into the auroral region, it is (first) depleted due to the rapid energization associated with wave-particle interactions (WPI) and then it is slowly replenished due to the effect of the LAE. (5) In general, the cases of summer-solar maximum and winter-solar minimum produce the two extreme results, while the other two cases (summer-solar minimum and winter-solar maximum) produce intermediate results. For example, the largest O+ escape fluxes were found for the case of (summer-solar maximum) and the smallest fluxes were found for the case of (winter-solar minimum).

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