The plasma sheet boundary layer

Abstract

The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three‐dimensional velocity‐space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockheed ion mass spectrometers indicate that ionospheric ions play a crucial role in magnetotail dynamics. Eleven crossings from the lobes to the central plasma sheet taken at various local times and levels of geomagnetic activity are analyzed in detail. The average ratios of He+/H+, He++/H+, and O+/H+ are not significantly different between the plasma sheet boundary layer and central plasma sheet. Densities and temperatures intermediate between the central plasma sheet and lobes are observed in the plasma sheet boundary layer although bulk flow speeds there are typically enhanced. Counter‐streaming ion beams are often observed in the plasma sheet boundary layer at energies of ∼1 keV/q to >45 keV/q. Intense antisunward‐flowing beams of ionospheric origin at E/q of <1 kV are often seen in the tail lobes, the plasma sheet boundary layer, and, infrequently, in the central plasma sheet. Such beams are not commonly observed in the central plasma sheet, which is characterized by hotter and more isotropic ion and electron distributions. Our samples of ion distributions in the plasma sheet boundary layer frequently show an evolution of distribution functions from highly anisotropic single beams or counter‐streaming beams toward the more isotropic distributions typical of the hot component of the central plasma sheet. Provided that the acceleration process for these beams can be identified, we can then account for the transport and injection of hot plasma into the central plasma sheet. We conclude that the plasma sheet boundary layer is a primary transport region of the magnetotail.

Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles

“…The ®rst of them emphasised that discrete auroras (hereafter we use this term in a more general sense as the name for very structured precipitation) are often seen in the poleward part of the auroral precipitation (referred to in the following as the auroral zone, to retain the original name``oval'' for the statistical pattern of the discrete forms). Lyons and Evans (1984) and Lyons et al (1988) suggested that they come from the outermost part of the magnetotail current sheet and associated this precipitation with the plasma-sheet boundary layer (PSBL) population (Eastman et al, 1984). This type of situation is quite typical for the recovery phase of a substorm where the so-called``double oval'' is formed (Elphinstone et al, 1995); it is also typical for long-duration events of the steady magnetospheric convection (SMC) (e.g.…”

Spatial structure of the plasma sheet boundary layer at distances greater than 180 R&lt;sub&gt;E&lt;/sub&gt; as derived from energetic particle measurements on GEOTAIL

“…In the distant tail the PSBL represents the layer of reconnected ®eld lines lying between the separatrix and the thermal plasma sheet (Richardson and Cowley, 1985). Tailward-streaming cold ion beams of ionospheric origin at energies less than 1 keV are also frequently observed in the PSBL (Parks et al, 1984;Eastman et al, 1984).…”

“…The plasma-sheet boundary layer (PSBL) is the region between the plasma sheet and the tail lobes, comprised of highly anisotropic ion distributions (Lui et al, 1978;DeCoster and Frank, 1979;Mobius et al, 1980;Spjeldvik and Fritz, 1981;Williams, 1981;Eastman et al, 1984Eastman et al, , 1985Sarris, 1990, 1991a, b). In the distant tail the PSBL represents the layer of reconnected ®eld lines lying between the separatrix and the thermal plasma sheet (Richardson and Cowley, 1985).…”

Multiple harmonic ULF waves in the plasma sheet boundary layer: Instability analysis

“…[2] The plasma sheet boundary layer (PSBL) was identified by Eastman et al [1984] and Parks et al [1984] as the temporally variable transition region in the Earth's magnetotail between the relatively dense central plasma sheet and the low-density magnetotail lobes, which are extensions of the Earth's polar cap regions. It is the primary region of mass, energy, and momentum transport in the magnetotail during quiet times [Eastman et al, 1985], although during more active periods bursty bulk flow events in the central plasma sheet are thought to dominate [Baumjohann et al, 1990;Angelopoulos et al, 1992Angelopoulos et al, , 1994.…”