A statistical study of nightside inverted-V events using Freja electron data: implications for the current-voltage relationship

We study a set of 47 nightside inverted-V events using the Freja F7 (Two-di mensional Electron Spectrometer; TESP) electron detector. For each data poi nt, we determine the peak potential, the source plasma density and temperat ure, and the field-aligned current density. We show that the temperature an d peak potential are correlated, which is in line with previous studies: th e temperature is on the average 3.3 times smaller than eV, where Vis the pe ak potential. On the contrary, the current density is statistically quite i ndependent of the potential. Thus, based on Freja F7 data, the observationa l current-voltage relationship is that the current is constant with respect to the voltage in an average sense. The formation of a parallel electric f ield, represented by the voltage, is more related to the source plasma dens ity and temperature and density than the current. Our results concern energ ies up to 8.7 keV. (C) 2000 Elsevier Science Ltd. All rights reserved.