High- and low-altitude observations of adiabatic parameters associated with auroral electron acceleration

Electron density and temperature, adiabatic thermal current, and field-alig ned conductivity have been estimated on the basis of observations by the De fense Meteorological Satellite Program (DMSP) satellites above the auroral oval and from measurement by the Active Magnetospheric Particle Tracer Expl orers/Ion Release Module (IRM) satellite in the near-Earth plasma sheet. We found that the estimated densities are comparable between these two satell ites, while the temperatures obtained from an accelerated Maxwellian fittin g procedure used on the DMSP spectra are far lower than those measured by I RM in the near-Earth plasma sheet. From this temperature discrepancy we con clude that tl le accelerated electrons do not come from the equatorial plan e of the magnetosphere but from the region just above the field-aligned pot ential difference at an altitude of a few ne. The DMSP data show that a lar ge field-aligned potential difference, which accelerates auroral electrons downward, is formed in the region with low field-aligned conductivity. The IRM data show that the field-aligned conductivity decreases with increasing X-GSM distance, increasing AE index, and after earthward high-speed how pa ssage. The adiabatic thermal current estimated from the IRM data is found t o be not enough to supply typical auroral current. Though tl le mechanism t hat produces field-aligned potential difference has not been identified yet , these results suggest that field-aligned potential difference is formed t o keep the balance between the field-aligned current generated by magnetosp heric processes and the current carried away from the generator region by a ccelerated electrons.