CHARACTERISTIC FEATURES OF ELECTRON-TEMPERATURE AND DENSITY VARIATIONS IN FIELD-ALIGNED CURRENT REGIONS

Observations by the thermal electron energy distribution (TED) instrument on board the Akebono (EXOS - D) satellite show that variations in electron temperatures, at altitudes from 300 to 2300 km, are closely related to field-aligned current (FAC) structures. At higher altitudes, electron temperatures increase in upward FAC regions and decrease in regions of downward FAC, while at the lower altitudes only temperature increases in upward FAC and adjacent regions are observed. Electron temperature variations were also found to be related to the number density of ambient electrons and the field-aligned current density. A numerical simulation is carried out to examine energetic particle precipitation and Joule dissipation as a possible mechanism for the observed temperature variations using the electron energy equation. In the present study, we focus the simulations on the temperature increase. Thermal electrons are found to be efficiently heated by Joule dissipation at lower altitudes; however, for increasing altitudes, energetic particle precipitation becomes the major heating source. These conclusions are supported by TED observations at low altitudes (<500 km); however, an additional heat source is required to explain the observed higher-altitude (>800 km) temperature increases.