Characteristics of auroral electron acceleration regions observed by Atmosphere Explorer C
Measurements of electron precipitation and ion drift velocities on the spacecraft Atmosphere Explorer C have revealed that electron acceleration regions (or inverted 'V's') in the 1200--1800 MLT quadrant exhibit the following systematic behavior: (1) Electron distribution functions in the acceleration regions are in all cases well described by Maxwellian primary electron beams which have been accelerated through an electrostatic potential V/sub 0/. (2) The typical inverted V latitudinal structure is always observed in the acceleration regions, with V/sub 0/ increasing to a maximum and subsequently decreasing to near zero over distances of approx.100 to approx. 250 km. (3) In all cases the Maxwellian temperature E/sub 0/ of the primary electron beam increases systematically with increases in V/sub 0/. (4) Rather weak acceleration regions, characterized by V/sub 0/approximately-less-than1 keV and E/sub 0/ values of approx.100 to approx.350 eV, occur in the cusp and in the highest-latitude portion of the dusk side electron precipitation zone, where the ionospheric convection velocity is beginning to rotate from antisunward to sunward. (5) Values of V/sub 0/ and E/sub 0/ and the width of the acceleration regions in the cusp and near dusk are similar, this fact together with observation 4 suggesting that both regions are connected to the magnetosheath. (6) Near dusk, regions of much stronger acceleration, characterized by V/sub 0/ values of approx.3 to over 10 keV and E/sub 0/ values in the approx.1-keV range, typically overlap well into the sunward convection region, at times lying completely within it, this behavior suggesting a link with the plasma sheet. (7) The acceleration regions in the sunward convection zone are associated with significant weakening of ionospheric convection velocities relative to the adjacent regions, resulting perhaps from conductivity enhancements produced by the very high electron fluxes that occur within them. (AIP)
- Research Organization:
- Magnetospheric and Plasma Physics Branch, NASA Marshall Space Flight Center, Huntsville, Alabama 35812
- OSTI ID:
- 7359959
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 81:13
- Country of Publication:
- United States
- Language:
- English
Similar Records
Properties of spikelike shear flow reversals observed in the Auroral plasma by atmosphere explorer C
Characteristics of ionospheric convection and field-aligned current in the dayside cusp region