Origin and geometry of upward parallel electric fields in the auroral acceleration region

Abstract

Abstract. Electric fields, magnetic fields, and plasmas measured on the Polar satellite are studied to determine the altitude extent of the upward field-aligned current portion of the auroral acceleration region and the physical processes that populate it with parallel electric fields. This region extends upward to a geocentric altitude of 3 or 3.5 Earth radii at premidnight local times during the spring and fall. In a model for this region a necessary but not sufficient condition for the appearance of parallel electric fields is an upward field-aligned current. Parallel electric fields will exist where the plasma density is insufficient to carry this imposed field-aligned current through the converging magnetic field. These parallel fields are associated with (1) high-altitude electron acceleration required to carry the imposed current through the low-density region; (2) a low-altitude sheath required to inject compensating positive charge into the region and to restrict entry of secondary electrons from below; and (3) the midaltitude maintenance of local charge neutrality. The parallel electric field in the low-altitude sheath is directly measured to be as large as several hundred mV m -l, while the higher-altitude fields appear to l•ave magnitudes of a few mV m -1 . The low-altitude sheath is corrugated in a manner that does not depend on striations of the field-aligned current but that may depend on density variations.

Beam effect on electromagnetic ion-cyclotron waves with general loss – cone distribution function in an anisotropic plasma-particle aspect analysis

“…In areas of upward current, large amplitude electromagnetic waves with frequencies within 5% of the local proton gyrofrequency p and its harmonics are often observed where an upstreaming ion beam exist (Chaston et al, 2002). The upgoing ion beams are reported by the S3-3 satellite (Shelley et al, 1976;Mozer et al, 1977) and by the Polar satellite data (Mozer and Hull, 2001). Ions are often observed to have been accelerated transversely to the background magnetic field in the auroral region (Sharp et al, 1977;Lund et al, 2001).…”

“…Horne and Thorne (1997) have found a correlation between periods of EMIC waves activity and pitch angle distributions, which resembles an "X" in velocity space and may be the signature of loss-cone G. Ahirwar et al: Beam effect on electromagnetic ion-cyclotron waves 559 distributions. The ion beam measured by Mozer and Hull (2001) has been considered to enter the plasma which follows the loss-cone distribution function. The results are compared with those derived by Kennel and Petschek (1966).…”

parallel electric fields in discrete arcs

“…FAST observations also suggest both highand low-altitude acceleration regions ]. Recent Polar observations now conclude that the majority of auroral acceleration is below 2 R E in altitude [Mozer and Hull, 2000].…”

Mesoscale PIC simulation of double layers and electron holes affecting parallel and transverse accelerations of electrons and ions

“…[2] Double layers (DLs) and electron holes (EHs) play significant roles in auroral acceleration processes [Ergun et al, 1998;Carlson et al, 1998;Mozer and Kletzing, 1998;McFadden et al, 1999;Mozer and Hull, 2001;Hull et al, 2010]. The formation of EHs in plasma permeated by electron beams has been known since the early work of Roberts and Berk [1967] and Morse and Nielson [1969].…”