Relationships between auroral particle distributions and magnetic field perturbations associated with field‐aligned currents

Abstract

Simultaneous measurements of magnetic fields and soft particle distributions in the topside auroral ionosphere reveal the relationships between field‐aligned currents and primary and secondary auroral particles. In the evening MLT sector the region 2 field‐aligned currents, which are directed into the ionosphere, are found to extend on the average 2.4° of invariant latitude equatorward of the low‐latitude boundary of 1‐keV electron precipitation from the magnetospheric plasma sheet. This current system is found to lie within the mid‐latitude total ion trough, as defined by its topside density depletion. This is a region predominantly void of particles between 5 eV and 15 keV. The current carriers are inferred to be upward flowing cold ionospheric electrons. At higher latitudes in the premidnight sector the region 1 field‐aligned current system lies within the region of particle precipitation and terminates at its high‐latitude boundary coincidently with the termination of energized precipitating particle fluxes. The primary reversal from downward to upward flowing field‐aligned currents may be quite sharp or may occur over several degrees of latitude. The current reversal is not necessarily associated with any particular particle precipitation structure.

The spatial distribution of region 2 field-aligned currents relative to subauroral polarization stream

“…Klumpar (1979) found that R2 FACs extend on average 2.4 • equatorward of the electron-precipitation boundary. Gussenhoven et al (1983) reported that the ion-precipitation boundary is 1.4 • equatorward of the electron boundary, the separation often reaches up to 3 and even 5 • in latitude.…”

Auroral plasmas in the evening sector: Satellite observations and theoretical interpretations

“…These ions show a pitch angle distribution with a relative minimum in the upward direction (~ ~ 180 ~ in the northern hemisphere and e ~ 0 ~ in the southern hemisphere) and with a relative maximum at an intermediate pitch angle in the upward hemisphere, thus forming an upflowing cone in velocity space, such as shown in Figure 9b. These are sometimes referred to as conics (from the shape of the velocity space distribution such as Figure 9b) and sometimes referred to as transversely accelerated ions (TAI) (Klumpar, 1979). Conical distributions have been observed at altitudes as low as 400 km (Whalen et aL, 1978) and up to at least 8000 km (Sharp et al, 1977;Ghielmetti et aL, 1978;Klumpar, 1979;Fennell etal., 1979;Gorney etal., 1981).…”

“…These are sometimes referred to as conics (from the shape of the velocity space distribution such as Figure 9b) and sometimes referred to as transversely accelerated ions (TAI) (Klumpar, 1979). Conical distributions have been observed at altitudes as low as 400 km (Whalen et aL, 1978) and up to at least 8000 km (Sharp et al, 1977;Ghielmetti et aL, 1978;Klumpar, 1979;Fennell etal., 1979;Gorney etal., 1981).…”

Relationships between field-aligned currents, electric fields, and particle precipitation as observed by Dynamics Explorer-2

“…Numerous papers have been written on this subject since then, using particle flux measurements or optical observations of the aurora and the field-aligned current data deduced from magnetic field measurements or from incoherent scatter radar observations (e.g., Klumpar, 1979;Burke et al, 1980;Robinson et al, 1982;Senior et al, 1982).…”