Energy and pitch angle-dispersed auroral electrons suggesting a time-variable, inverted-V potential structure

High temporal resolution electron detectors aboard the PHAZE II rocket flig ht have shown that the energy-dispersed, field-aligned bursts (FABs) are ti me coincident with pitch angle-dispersed electrons having energies at the m aximum voltage of the inverted-V potential. This modulation of the energeti c inverted-V electrons is superimposed upon an energy-diffused background r esulting in a peak-to-valley ratio of similar to 2 for the pitch angle-disp ersed electrons. Since the characteristic energy of the FABs, the order of an eV, is considerably less than that of the plasma sheet electrons (the or der of a keV) presumably falling through the inverted-V potential to create the discrete aurora, the modulation mechanism has to be independent of the electron temperature. The mechanism must accelerate the cold electrons ove r a range of energies from the inverted-V energy down to a few tens of eV. It must do this at the same time it is creating a population of hot, pitch angle-dispersed electrons at the inverted-V energy. Both the energy dispers ion of the FABs and the pitch angle dispersion of the inverted-V electrons can be used to determine a source height assuming both populations start fr om the same source region at the same time. These calculations give source heights between 3500 and 5300 km for various events and disagreement betwee n the two methods the order of 20%, which is within the rather substantial error limits of both calculations. A simple mechanism of providing a common start time for both populations of electrons would be a turning on/off of a spatially limited (vertically), inverted-V potential. The energy-disperse d FABs can be reconstructed at rocket altitudes if one assumes that cold el ectrons are accelerated to an energy determined by how much of the inverted -V potential they fall through when it is turned on. Similarly, the pitch a ngle-dispersed, inverted-V electrons can be modeled at rocket altitudes if one assumes that the plasma sheet electrons falling through the entire pote ntial drop all start to do so at the same time when the potential is turned on. The FABs seem to fluctuate at either similar to 10 Hz or near 100 Hz. An important constraint of the on/off mechanism is whether cold electrons ( 1 eV) can fill the inverted-V volume during the off cycle. The maximum vert ical height of the 10 kV potential region for the 10 Hz events would be the order of 100 and 10 km for the 100 Hz events. To get 10 kV, these heights require parallel electric fields of 0.1 and 1 V/m respectively for the 10 a nd 100 Hz events assuming that the filling is along B from below the invert ed-V potential. Alternative mechanisms are also discussed in the light of t he data presented.