Spatial relationships between field-aligned currents and suprathermal electron beams observed at the poleward boundary of the nightside auroral oval

Details Spatial relationships between field-aligned currents and suprathermal electron beams observed at the poleward boundary of the nightside auroral oval Spatial relationships between field-aligned currents and suprathermal electron beams observed at the poleward boundary of the nightside auroral oval

Feb 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995jgr...100.1625n&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 100, no. A2, p. 1625-1637

Physics

7

Auroras, Electrons, Energy Spectra, Field Aligned Currents, Magnetosheath, Plasma Sheaths, Electron Density (Concentration), Exos-D Satellite, Geomagnetism, Maxwell-Boltzmann Density Function, Pitch (Inclination)

Scientific paper

Magnetic field and particle data obtained from the Akebono satellite in the period from December 1989 to February 1990 are used for examining the relationships between electron populations and field-aligned currents in the poleward boundary region of the nightside auroral oval. It is found that suprathermal electron beams frequently observed at the poleward boundary of the auroral oval associated with a latitudinally narrow (approx. 1 deg) field-aligned current system located at the poleward edge, which has been designated as 'the boundary current system' by Fukunishi et al. (1993). In addition, an unstructured band of plasma-sheet-like electrons with isotropic pitch angle distributions except for loss cone appears through the auroral oval including the boundary current region. As a result, the electron energy spectra at the poleward boundary are characterized by a superposition of two Maxwellian functions: the isotropic high-temperature component and the field-aligned low-temperature component. From the Maxwellian fitting procedure, the temperature and the density of the high-temperature component are estimated to be 0.3 - 1.7 keV and less than or equal to 1.0/cu cm, respectively, and those of the low-temperature component are estimated to be 10 - 80 eV and 2 - 16/cu cm, respectively. An important finding is that the temperature and the density of the low-temperature conponent and the density of the high-temperature component are significantly enhanced in the upward current region occupying the equatorward portion of the boundary current system, while the temperature of the high-temperature component is nearly constant throughout this region. These characteristics strongly suggest that the high-temperature component originates from plasma sheet electrons, while the low-temperature component originates from ionospheric electrons. It is likely that ionospheric thermal electrons flow away from the polewardmost downward current region into the magnetosphere and are accelerated and heated by some wave-particle interaction process during their inward motion due to E x B drift.

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