Detection of localized, plasma‐depleted flux tubes or bubbles in the midtail plasma sheet

Сергеев, В. А.; Angelopoulos, V.; Gosling, J. T.; Cattell, C. A.; Russell, C. T.

doi:10.1029/96ja00460

Cited by 300 publications

(421 citation statements)

References 19 publications

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“…Intensifications of the electric fields correspond to local depletions of the plasma pressure. While a net increase in plasma pressure has often been observed in the inner plasma sheet [e.g., Miyashita et al, 2009;Xing et al, 2010], the local depletion of the plasma pressure that we observed is similar to the one observed in the midtail plasma sheet (∼20 R E ), where earthward flows enhance with entropy reduction [e.g., Sergeev et al, 1996].…”

Section: The Westward Expansion On 26 February 2008mentioning

confidence: 55%

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

et al. 2011

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[1] Fast azimuthal auroral expansion and poleward expansion are characteristic features of the expansion phase of substorms. In the first study of its kind, we have investigated the azimuthal auroral expansion and its magnetospheric counterpart using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imagers and multiple spacecraft. During the tail season in 2008-2009, we found 16 events of azimuthally expanding aurora that passed near the magnetic footprints of the multiple spacecraft operating in the near-Earth plasma sheet. In the magnetosphere, these events commonly showed fast azimuthal and earthward flows associated with intense electric fields and magnetic dipolarization. The speed of the propagating structure, which was estimated from the time difference of the depolarization observed by the multiple spacecraft, was close to the measured azimuthal plasma flow velocity. We also found that this azimuthal plasma transport was dominated by the E × B drift speed associated with the enhanced electric field. In a statistical analysis, the averaged speeds of the leading edge of the westward and eastward auroral expansion were 8.8 and 5.3 km/s, respectively. When mapped onto the equatorial magnetosphere, these speeds (267 and 162 km/s) were comparable to the averaged azimuthal plasma (E × B) flow speeds observed by the spacecraft, which were 193 (239) km/s in the westward direction and 112 (139) km/s in the eastward direction. Our events showed that E × B flows and auroral expansion predominantly propagated westward, indicating an effect of westward background convection in the Harang flow shear. From these results, we concluded that the azimuthal auroral expansion was closely related to magnetic dipolarization which expanded azimuthally at the E × B drift speed. On the basis of the abrupt formation of the fast E × B flows and their propagation away from the onset location, we suggest that the effects of the intense large-scale electric fields, which are possibly generated through substorm onset turbulence, propagate to the ionosphere along the magnetic field lines and lead to azimuthal expansion of an auroral arc.

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Section: The Westward Expansion On 26 February 2008mentioning

confidence: 55%

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

et al. 2011

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“…Azimuthal perturbations of the magnetic ®eld and velocity measurements associated with BBFs were also discussed by Baumjohann et al (1990), who suggested an association with the limited azimuthal extent of the¯ow region. Some evidence of a systematic relationship between the direction of the V y perturbation and the azimuthal location of the observing spacecraft, such that V y was directed away from the midnight sector, has recently been presented by Sergeev et al (1996) at a distance of 20 R E downtail, who interpreted BBFs in terms of plasma sheet bubbles (Chen and Wolf, 1993), probably caused by reconnection in the magnetotail. Indeed, the ground magnetometer features presented here are similar to those of Kauristie et al (1996), which were again interpreted in terms of plasma sheet bubbles.…”

Section: Relationship To Substorm Theoriesmentioning

confidence: 99%

Simultaneous ionospheric and magnetospheric observations of azimuthally propagating transient features during substorms

1998

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Abstract. During the 6 th August 1995, the CUTLASS Finland HF radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14 s. Data from such scans, during the substorm expansion phase, revealed pulses of equatorward¯ow exceeding $600 m s A1 with a duration of $5 min and a repetition period of $8 min. Each pulse of enhanced equatorward¯ow was preceded by an interval of suppressed¯ow and enhanced ionospheric Hall conductance. These transient features, which propagate eastwards away from local midnight, have been interpreted as ionospheric current vortices associated with ®eld-aligned current pairs. The present study reveals that these ionospheric convection features appear to have an accompanying signature in the magnetosphere, comprising a dawnward perturbation and dipolarisation of the magnetic ®eld and dawnward plasma¯ow, measured in the geomagnetic tail by the Geotail spacecraft, located at L = 10 and some four hours to the east, in the postmidnight sector. These signatures are suggested to be the consequence of the observation of the same ®eld aligned currents in the magnetosphere. Their possible relationship with bursty Earthward plasma¯ow and magnetotail reconnection is discussed.

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“…[60] Comparing the ECR and BBF scale sizes, observational investigations have confirmed that BBFs are narrow and elongated structures, whose cross-tail scale size is of the order of 1 or a few R E [e.g., Sergeev et al, 1996a;Angelopoulos et al, 1997;Nakamura et al, 2004Nakamura et al, , 2005aWalsh et al, 2009]. Walsh et al [2009] estimated that the BBF size along the direction of the plasma flow is approximately ∼4R E .…”

Section: Ecr Scale Sizementioning

confidence: 99%

“…As shown by Birn et al [2004], flow vortices appear at the flanks of the bubble, twisting the magnetic field, and causing a downward (upward) field-aligned current at the dawnside (duskside) flank, and forming a local wedge like current system [e.g., Wolf, 1993, 1999;Sergeev et al, 1996a;Birn and Hesse, 1996;Birn et al, 1999Birn et al, , 2004Snekvik et al, 2007;Zhang et al, 2009]. A return plasma flow may occur at the flanks of the bubble, and the corresponding shear against the plasma flow in the bubble main channel may also be involved in the generation of the field-aligned currents [e.g., Chen and Wolf, 1999;Kauristie et al, 2000;Birn et al, 2004;Keiling et al, 2009;Ohtani et al, 2009;Walsh et al, 2009;Panov et al, 2010aPanov et al, , 2010bBirn et al, 2011;Ge et al, 2011;Pitkänen et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

Energy conversion regions as observed by Cluster in the plasma sheet

et al. 2011

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[1] In this article we present a review of recent studies of observations of localized energy conversion regions (ECRs) observed by Cluster in the plasma sheet at altitudes of 15-20R E . By examining variations in the power density, E · J, where E is the electric field and J is the current density, we show that the plasma sheet exhibits a high level of fine structure. Approximately three times as many concentrated load regions (CLRs) (E · J > 0) as concentrated generator regions (CGRs) (E · J < 0) are identified, confirming the average load character of the plasma sheet. Some ECRs are found to relate to auroral activity. While ECRs are relevant for the energy conversion between the electromagnetic field and the particles, bursty bulk flows (BBFs) play a central role for the energy transfer in the plasma sheet. We show that ECRs and BBFs are likely to be related, although details of this relationship are yet to be explored. The plasma sheet energy conversion increases rather simultaneously with increasing geomagnetic activity in both CLRs and CGRs. Consistent with large-scale magnetotail simulations, most of the observed ECRs appear to be rather stationary in space but varying in time. We estimate that the ECR lifetime and scale size are a few minutes and a few R E , respectively. It is conceivable that ECRs rise and vanish locally in significant regions of the plasma sheet, possibly oscillating between load and generator character, while some energy is transmitted as Poynting flux to the ionosphere.

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Detection of localized, plasma‐depleted flux tubes or bubbles in the midtail plasma sheet

Cited by 300 publications

References 19 publications

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

Simultaneous ionospheric and magnetospheric observations of azimuthally propagating transient features during substorms

Energy conversion regions as observed by Cluster in the plasma sheet

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