Anisotropy Reversals in the Distant Magnetotail and Their Association with Magnetospheric Substorms

Angelopoulos, V.; Lui, A. T. Y.; McEntire, R. W.; Williams, D. J.; Christon, S. P.; Nakamura, Masato; Kusaka, Hajime; Mukai, T.; Kokubun, S.; Yamamoto, T.; Reeves, G. D.; Friis‐Christensen, E.; Hughes, W. J.

doi:10.5636/jgg.48.629

Cited by 6 publications

(3 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our observation from Geotail that anisotropy reversals are quite common in the region Earthward of 100 RE suggests that the tailward retreat of the acceleration region deserves further study in a statistical manner. The study of an extended period of activity byAngelopoulos et al [1996b] has corroborated the repeatability of the phenomenon and concluded that the median time delay between substorm onset and tailward retreat of the acceleration region past x = -90 R E was between 61 and 94 minutes. One of the questions that ought to be answered is what controls the distance to which the acceleration centers retreat.Solar wind conditions are an important factor and should be considered in such a study.…”

mentioning

confidence: 78%

Tailward progression of magnetotail acceleration centers: Relationship to substorm current wedge

Angelopoulos¹,

Mitchell²,

McEntire³

et al. 1996

J. Geophys. Res.

Self Cite

View full text Add to dashboard Cite

During a fortuitous near‐alignment of the IMP 8 and Geotail spacecraft along the magnetotail axis, geomagnetic activity monitors on the ground and at geosynchronous altitude detected the evolution of a magnetospheric substorm. We searched for evidence of the neutral line formation and evolution during this substorm. There exists evidence for multiple, time‐varying, localized (<9 RE) acceleration regions in the magnetotail at the time. Late in the expansion phase of the substorm a reversal of the predominant direction of the energetic particle anisotropy as well as the plasma flow velocity from tailward to Earthward was observed at Geotail at X=−61 RE. The tailward‐to‐Earthward anisotropy reversal is consistent with a tailward progression of the acceleration centers at Geotail. This phenomenon could be identified as the tailward retreat of the neutral line. However, the tailward progression of the activity is in reality the re appearance of new acceleration regions at gradually more tailward sites. Although the large temporal and spatial development is consistent with that of a reconnection geometry, the local Geotail acceleration is bursty and quite possibly localized. An ensuing increase of the northward magnetic field component seen at IMP 8 at X =−32 RE is consistent with a tailward expansion of the substorm current wedge out to that distance. Current wedge formation at IMP 8 was delayed by several minutes relative to the anisotropy reversal at Geotail. We interpret this as evidence that the location of current wedge and the location of magnetotail particle acceleration are separated by at least 30 RE during the late expansion phase of this substorm. Given the ∼9 RE cross‐tail separation of IMP 8 and Geotail, there still exists some uncertainty as to the three dimensional evolution of the acceleration and dipolarization regions in the late expansion phase of this substorm. Given the scarcity of similar IMP 8‐Geotail conjunctions during the distant tail Geotail phase, a full understanding of that evolution has to await a future multiprobe mission.

show abstract

mentioning

confidence: 78%

Tailward progression of magnetotail acceleration centers: Relationship to substorm current wedge

Angelopoulos¹,

Mitchell²,

McEntire³

et al. 1996

J. Geophys. Res.

Self Cite

View full text Add to dashboard Cite

show abstract

“…If the downtail propagation velocity of the acceleration site is constant, then the speed is $205 km s A1 (i.e., 160 R E divided by 82 min). Angelopoulos et al (1996) found a speed 75±115 km s A1 out of 14 substorms, while GEOTAIL was located at A90 R E .…”

Section: Discussionmentioning

confidence: 99%

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

et al. 1997

Self Cite

View full text Add to dashboard Cite

Abstract. We have analyzed the onsets of energetic particle bursts detected by the ICS and STICS sensors of the EPIC instrument on board the GEOTAIL spacecraft in the deep magnetotail (i.e., at distances greater than 180 R E ). Such bursts are commonly observed at the plasma-sheet boundary layer (PSBL) and are highly collimated along the magnetic ®eld. The bursts display a normal velocity dispersion (i.e., the higher-speed particles are seen ®rst, while the progressively lower speed particles are seen later) when observed upon entry of the spacecraft from the magnetotail lobes into the plasma sheet. Upon exit from the plasma sheet a reverse velocity dispersion is observed (i.e., lower-speed particles disappear ®rst and higher-speed particles disappear last). Three major ®ndings are as follows. First, the tailwardjetting energetic particle populations of the distant-tail plasma sheet display an energy layering: the energetic electrons stream along open PSBL ®eld lines with peak uxes at the lobes. Energetic protons occupy the next layer, and as the spacecraft moves towards the neutral sheet progressively decreasing energies are encountered systematically. These plasma-sheet layers display spatial symmetry, with the plane of symmetry the neutral sheet. Second, if we consider the same energy level of energetic particles, then the H + layer is con®ned within that of the energetic electron, the He ++ layer is con®ned within that of the proton, and the oxygen layer is con®ned within the alpha particle layer. Third, whenever the energetic electrons show higher¯uxes inside the plasma sheet as compared to those at the boundary layer, their angular distribution is isotropic irrespective of the Earthward or tailward character of¯uxes, suggesting a closed ®eld line topology.

show abstract

“…[16] It has been suggested that distant tail high speed flows could originate from a tailward-retreating near-Earth neutral line in the later stages of a substorm [Angelopoulos et al, 1996]. However, for the event presented here the AU, AL, and AE indices (Figure 2b) displayed very low auroral geomagnetic activity.…”

Section: Geomagnetic Activitymentioning

confidence: 84%

Distant magnetotail reconnection and the coupling to the near‐Earth plasma sheet: Wind and Geotail case study

Øieroset

Phan

Fujimoto

et al. 2004

Geophysical Research Letters

View full text Add to dashboard Cite

We have studied the coupling between the distant and near‐Earth plasma sheet during an 8 hour interval on April 1, 1999 when the interplanetary magnetic field was northward and dominated by the By component. During these 8 hours the Geotail spacecraft sampled the near‐Earth magnetotail at XGSM ∼ −25 RE while the Wind spacecraft was located in the distant magnetotail at XGSM ∼ −60 RE. Wind detected long duration (>8 hours) and likely spatially extended convective high speed flows indicative of continuous magnetic reconnection, whereas only plasma sheet boundary layer beams and some locally generated bursty bulk flows were observed at the Geotail location. Hence the high speed distant tail reconnection flows did not reach the near‐Earth plasma sheet at high speed. No apparent signatures of the long duration distant tail reconnection flows in terms of global and auroral geomagnetic activity were observed.

show abstract

Anisotropy Reversals in the Distant Magnetotail and Their Association with Magnetospheric Substorms

Cited by 6 publications

References 55 publications

Tailward progression of magnetotail acceleration centers: Relationship to substorm current wedge

Tailward progression of magnetotail acceleration centers: Relationship to substorm current wedge

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

Distant magnetotail reconnection and the coupling to the near‐Earth plasma sheet: Wind and Geotail case study

Contact Info

Product

Resources

About

Anisotropy Reversals in the Distant Magnetotail and Their Association with Magnetospheric Substorms

Cited by 6 publications

References 55 publications

Tailward progression of magnetotail acceleration centers: Relationship to substorm current wedge

Tailward progression of magnetotail acceleration centers: Relationship to substorm current wedge

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

Distant magnetotail reconnection and the coupling to the near‐Earth plasma sheet: Wind and Geotail case study

Contact Info

Product

Resources

About

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