New Results for the Self-Consistent Parallel E-Field and Particle Distributions in the Auroral Return Current Region

Details New Results for the Self-Consistent Parallel E-Field and Particle Distributions in the Auroral Return Current Region New Results for the Self-Consistent Parallel E-Field and Particle Distributions in the Auroral Return Current Region

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11c..06j&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SM11C-06

Physics

2704 Auroral Phenomena (2407), 2708 Current Systems (2409), 2712 Electric Fields (2411)

Scientific paper

The auroral return current region is characterized by: diverging electrostatic shocks and a downward pointing parallel E-field (E); upflowing low energy field-aligned electrons; intense transverse ion heating; small-scale density cavities; and intense ELF and VLF electric-field turbulence. Most of these features at lower altitudes can be explained using a Fokker-Planck theory where we assume that a fraction of the broadband ELF electric-field fluctuations is real, time-domain turbulence in the left-hand circular polarized component and heats the ions by a resonant interaction near the cyclotron frequency. The electron and ion distribution functions and E evolve self-consistently on the flux tube in response to the demand for current and/or voltage. See Jasperse, Geophys. Res. Lett., 25, 3485, 1998 and Jasperse and Grossbard, IEEE Transactions on Plasma Science, 28, 1874, 2000. The major deficiency with this theory is that it produces a parallel potential that increases indefinitely with distance along the flux tube and particle distributions that are unrealistic beyond several earth radii. Recently, statistical studies of the return current region based on FAST data ( ~2000 to 4000 km) by Lynch et al. (J. Geophys. Res., in press) reveal that the electric-field spectral density at the oxygen ion gyrofrequency is highly correlated with the steady-state value of j.E. Assuming this to be the case on the entire flux tube from the bottom of the acceleration region to several earth radii and beyond, we may solve the Fokker-Planck equations self-consistently for the particle distributions and E. In doing so, we use the electric-field spectral density determined by FAST at the satellite altitude. At high altitudes, the parallel potential tends to a constant, E is negative and tends to zero, and the ion conics fold up to near beam-like structures. We show that these results for the return current region agree with FAST data at low altitudes ( ~2000 to 4000 km) and INTERBALL data at high altitudes (>20000).

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