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

Sarafopoulos, D. V.; Sarris, E. T.; Angelopoulos, V.; Yamamoto, T.; Kokubun, S.

doi:10.1007/s00585-997-1246-0

Cited by 10 publications

(9 citation statements)

References 27 publications

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“…In this case, ion distributions in the near‐Earth PSBL are controlled only by the velocity filter (VF) effect owing to magnetotail convection which produces the equatorward drift of accelerated ions while they are moving from the source to the observation point. The character of energy dispersion should then depend on the direction of the PSBL crossing: high‐energy ions are observed first when the spacecraft moves from the lobe toward the NS and they disappear last when a spacecraft traverses the PSBL in the opposite direction [e.g., Sarris and Axford , 1979; Williams , 1981; Andrews et al , 1981; Takahashi and Hones , 1988; Sarafopoulos et al , 1997; Sauvaud and Kovrazhkin , 2004]. This theory accounts for the formation of “global” spatial energy dispersion in the PSBL.…”

Section: Introductionmentioning

confidence: 99%

“Geography” of ion acceleration in the magnetotail: X‐line versus current sheet effects

et al. 2009

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Field‐aligned ion beams are often observed in the Plasma Sheet Boundary Layer (PSBL) of Earth's magnetotail. We studied two types of ion beams observed in the magnetotail at different times. Both types of ion beams are pitch angle‐collimated along the magnetic field direction but they differ significantly with the width of ion velocity distribution functions in parallel energies. The first type represents energy‐collimated ion beams with observed durations of 3–23 min. The majority of such beams have energies ≤20 keV. Together with such ion beams, isotropic electron distributions are observed. We suggest that such ion beams are accelerated at spatially localized regions located rather far from the distant X‐line where magnetic field lines are already closed. Another type of PSBL ion distributions represents wide in parallel energy ion beams with typical energies ≥ tens of keV. The registered durations of such beams are 1–6 min. They are observed together with anisotropic electron velocity distributions formed by the cold and hot counter‐streaming components. This feature is peculiar for the magnetic separatrix and indicates that the spacecraft crosses still open or very recently closed magnetic field lines. We have analyzed 987 crossings of the high‐latitude edge of the PSBL by Geotail at −220 RE < X < −20 RE. The majority of Type‐I ion beams are moving earthward at X ≥ −110 RE and so have their sources located earthward from the distant X‐line (at X < −110 RE). These ion beams were observed during quiet geomagnetic periods. More than 50% of Type‐II ion beams move tailward at X ≤ −50 RE. Thus their acceleration sources are located closer to Earth. Type‐II ion beams were observed during both quiet and disturbed periods. The energy distribution of the first type of ion beams along the dawn‐dusk direction approximately conforms to the assumption about their non‐adiabatic acceleration by the quasi‐steady dawn‐dusk electric field. On the other hand, we suggest that ion beams of the second type are generated in close proximity to the X‐line. The energy distribution of such ion beams along the Y direction indicates ion energization by a strong (presumably inductive) electric field, especially in cases of ion acceleration tailward from the X‐line.

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Section: Introductionmentioning

confidence: 99%

“Geography” of ion acceleration in the magnetotail: X‐line versus current sheet effects

et al. 2009

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“…Most importantly, measurements concerning streaming energetic electron fluxes are to a great degree valuable; their angular distributions are not affected by any bulk plasma flow and/or any drift toward the current sheet during their time of flight from the source to satellite. In contrast, the ion fluxes frequently form energy depended layered structures in the plasma sheet; for instance, impressive case studies extended in the whole plasma sheet were studied by Sarafopoulos et al, (1997).…”

Section: Introductionmentioning

confidence: 99%

Bi-layer structure of counterstreaming energetic electron fluxes: a diagnostic tool of the acceleration mechanism in the Earth's magnetotail

Sarafopoulos

2010

Ann. Geophys.

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Abstract.For the first time we identify a bi-layer structure of energetic electron fluxes in the Earth's magnetotail and establish (using datasets mainly obtained by the Geotail Energetic Particles and Ion Composition (EPIC/ICS) instrument) that it actually provides strong evidence for a purely spatial structure. Each bi-layer event is composed of two distinct layers with counterstreaming energetic electron fluxes, parallel and antiparallel to the local ambient magnetic field lines; in particular, the tailward directed fluxes always occur in a region adjacent to the lobes. Adopting the X-line as a standard reconnection model, we determine the occurrence of bi-layer events relatively to the neutral point, in the substorm frame; four (out of the shown seven) events are observed earthward and three tailward, a result implying that four events probably occurred with the substorm's local recovery phase. We discuss the bi-layer events in terms of the X-line model; they add more constraints for any candidate electron acceleration mechanism. It should be stressed that until this time, none proposed electron acceleration mechanism has discussed or predicted these layered structures with all their properties. Then we discuss the bi-layer events in terms of the much promising "akis model", as introduced by Sarafopoulos (2008). The akis magnetic field topology is embedded in a thinned plasma sheet and is potentially causing charge separation. We assume that as the R c curvature radius of the magnetic field line tends to become equal to the ion gyroradius r g , then the ions become non-adiabatic. At the limit R c =r g the demagnetization process is also under way and the frozen-in magnetic field condition is violated by strong wave turbulence; hence, the ion particles in this geometry are stochastically scattered. In addition, ion diffusion probably takes place across the magnetic field, since an intense pressure gradient is directed earthward; hence, Correspondence to: D. V. Sarafopoulos (sarafo@ee.duth.gr) ions are ejected tailward of akis. This way, in front of akis an "ion capsule region" is formed with net positive charge. In between them a distinct region with an electric field E ⊥ orthogonal to the magnetic field is emerged; E ⊥ in front of akis is directed earthward. The field-aligned and highly anisotropic energetic electron populations have probably resulted via spatially separated antiparallel and field-aligned electric fields being the very heart of the acceleration source. We assume that the ultimate cause for the field-aligned electric fields are the net positive capsule charge and the net negative charge trapped at the tip of akis; both charges will be eventually neutralized through field aligned currents, but they remain unshielded for sufficient time to produce the observed events.

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“…16, no ions will be detected, while at the SAT 1 (SAT 2) site tailward (earthward) ion fluxes would be detected. In contrast, highly streaming energetic ion populations could be seen, for instance at X ∼ =−180 R E (Sarafopoulos et al, 1997), whenever the reconnected field lines reach the separatrix.…”

Section: Contradiction In Terms Of a Symmetric Reconnection Modelmentioning

confidence: 99%

A physical mechanism producing suprathermal populations and initiating substorms in the Earth's magnetotail

Sarafopoulos

2008

Ann. Geophys.

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Abstract. We suggest a candidate physical mechanism, combining there dimensional structure and temporal development, which is potentially able to produce suprathermal populations and cross-tail current disruptions in the Earth's plasma sheet. At the core of the proposed process is the "akis" structure; in a thin current sheet (TCS) the stretched (tail-like) magnetic field lines locally terminate into a sharp tip around the tail midplane. At this sharp tip of the TCS, ions become non-adiabatic, while a percentage of electrons are accumulated and trapped: The strong and transient electrostatic electric fields established along the magnetic field lines produce suprathermal populations. In parallel, the tip structure is associated with field aligned and mutually attracted parallel filamentary currents which progressively become more intense and inevitably the structure collapses, and so does the local TCS. The mechanism is observationally based on elementary, almost autonomous and spatiotemporal entities that correspond each to a local thinning/dipolarization pair having duration of ∼1 min. Energetic proton and electron populations do not occur simultaneously, and we infer that they are separately accelerated at local thinnings and dipolarizations, respectively. In one example energetic particles are accelerated without any dB/dt variation and before the substorm expansion phase onset. A particular effort is undertaken demonstrating that the proposed acceleration mechanism may explain the plasma sheet ratio T i /T e ≈7. All our inferences are checked by the highest resolution datasets obtained by the Geotail Energetic Particles and Ion Composition (EPIC) instrument. The energetic particles are used as the best diagnostics for the accelerating source. Near Earth (X≈10 R E ) selected events support our basic concept. The proposed mechanism seems to reveal a fundamental building block of the substorm phenomenon and may be the basic process/structure, which is now missing, that might help exCorrespondence to: D. V. Sarafopoulos (sarafo@ee.duth.gr) plain the persistent, outstanding deficiencies in our physical description of magnetospheric substorms. The mechanism is tested, checked, and found consistent with substorm associated observations performed ∼30 and 60 R E away from Earth.

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

Cited by 10 publications

References 27 publications

“Geography” of ion acceleration in the magnetotail: X‐line versus current sheet effects

“Geography” of ion acceleration in the magnetotail: X‐line versus current sheet effects

Bi-layer structure of counterstreaming energetic electron fluxes: a diagnostic tool of the acceleration mechanism in the Earth's magnetotail

A physical mechanism producing suprathermal populations and initiating substorms in the Earth's magnetotail

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