Auroral potential structures and current-voltage relationship: Summary of recent results

Discrete auroral arcs are caused by precipitating accelerated electrons, an d there is a lot of observational evidence for the associated potential str ucture being U-shaped below about 15000 km altitude. However, according to our studies using Polar data at higher altitude, there is a lack of converg ent electric field signatures at similar to 20000-35000 km and consequently we suggest that the U-shaped potential contours close below this altitude range. To explain this finding, an O-shaped potential model is proposed, to gether with a maintenance mechanism which involves parallel energisation of middle-energy electrons by waves in the 15000-30000 km altitude range. Tes t particle simulations show that the presence of waves brings this "coopera tive" model in quantitative agreement with both Polar and low-altitude obse rvations. We also discuss our statistical Freja satellite studies of the ob servational relationship between the peak energy (voltage) and the current density in inverted-V regions. The result is that the current and voltage a re sometimes correlated in the evening sector events, but almost always ant icorrelated in the morning sector. This result, which is very interesting i n its own right, may also have some relationship to the potential structure question, (C) 2001 Elsevier Science Ltd. All rights reserved.