Statistical analysis of dipolarizations using spacecraft closely separated along Z in the near‐Earth magnetotail

Palin, L.; Jacquey, C.; Sauvaud, J. A.; Lavraud, B.; Budnik, E.; Angelopoulos, V.; Auster, U.; McFadden, J. P.; Larson, D. E.

doi:10.1029/2012ja017532

Cited by 10 publications

(17 citation statements)

References 25 publications

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“…All these properties confirm the Palin et al . [] results obtained from measurements farther away from the DF and are consistent with effects of tail reconnection in the course of substorms [ Coroniti , ].…”

Section: Resultssupporting

confidence: 58%

On the current sheets surrounding dipolarizing flux bundles in the magnetotail: The case for wedgelets

2013

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[1] Using Time History of Events and Macroscale Interactions during Substorms observations from four tail seasons, we study the three-dimensional structure of the dipolarization front current sheet (DFCS), which demarcates the magnetic boundary of a dipolarizing flux bundle (DFB, the strong magnetic field region led by a dipolarization front) in Earth's magnetotail. An equatorial cross section of the DFCS is convex; a meridional cross section is consistent with a dipolarized field line. The equatorial flow pattern in the ambient plasma ahead of the DFCS exhibits diversions of opposite sense on its evening and morning sides. The magnetic field perturbations are consistent with local field-aligned current generation of region-2 sense ahead of the front and region-1 sense at the front. The median thickness of the DFCS increases from 800 to 2000 km with increasing distance from the neutral sheet, indicating bundle compression near the neutral sheet. On a meridional cross section, DFCS's linear current density (1.2-1.8 nA/m) peaks~AE0.55 l from the neutral sheet (where l is the ambient cross-tail current sheet half-thickness, l~1.5 R E in our database). This peak, reminiscent of active-time cross-tail current sheet bifurcation noted in past studies, suggests that the intense but thin DFCS (10 to 20 nA/m 2 ) may be produced by redistribution (diversion) of the extended but weaker cross-tail current (~1 nA/m 2 ). Near the neutral sheet, the average DFCS current over the dipolarization front (DF) thickness is perpendicular to both the magnetic field interior to the DFB and the average field direction over the DF thickness. Away from the neutral sheet, the average current becomes progressively parallel to the internal field and the average field direction. The average current directions are indicative of region-1-sense field-aligned current on the DF. As few as approximately three DFBs can carry sufficient total current that, if redirected into the auroral ionosphere, can account for the substorm current wedge's peak current for a sizable substorm (~1 MA). A collapsing DFB could thus be an elemental substorm current wedge, or "wedgelet," that can divert a sizable portion of the cross-tail current into the auroral ionosphere.Citation: Liu, J., V. Angelopoulos, A. Runov, and X.-Z. Zhou (2013), On the current sheets surrounding dipolarizing flux bundles in the magnetotail: The case for wedgelets,

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Section: Resultssupporting

confidence: 58%

On the current sheets surrounding dipolarizing flux bundles in the magnetotail: The case for wedgelets

2013

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“…The total pressure has a small increase at DFB arrival time because of the enhanced magnetic field. This signature is similar to those of magnetotail DFBs [e.g., Palin et al ., ; Liu et al ., ]. In Figures f and g we plot the proton and electron fluxes from the MagEIS instrument.…”

Section: Case and Statistical Studiesmentioning

confidence: 99%

Dipolarizing flux bundles in the cis‐geosynchronous magnetosphere: Relationship between electric fields and energetic particle injections

et al. 2016

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Dipolarizing flux bundles (DFBs) are small flux tubes (typically <3 RE in XGSM and YGSM) in the nightside magnetosphere that have magnetic field more dipolar than the background. Although DFBs are known to accelerate particles, creating energetic particle injections outside geosynchronous orbit (trans‐GEO), the nature of the acceleration mechanism and the importance of DFBs in generating injections inside geosynchronous orbit (cis‐GEO) are unclear. Our statistical study of cis‐GEO DFBs using data from the Van Allen Probes reveals that just like trans‐GEO DFBs, cis‐GEO DFBs occur most often in the premidnight sector, but their occurrence rate is ~1/3 that of trans‐GEO DFBs. Half the cis‐GEO DFBs are accompanied by an energetic particle injection and have an electric field 3 times stronger than that of the injectionless half. All DFB injections are dispersionless within the temporal resolution considered (11 s). Our findings suggest that these injections are ushered or produced locally by the DFB, and the DFB's strong electric field is an important aspect of the injection generation mechanism.

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“…Palin et al . [] report on dipolarization fronts (presumably related to BBFs) all the way in to 7 R E geocentric distance, while Fu et al . [] report on a rapid decrease of the dipolarization front occurrence rate between 15 and 10 R E .…”

Section: Introductionmentioning

confidence: 99%

Magnetic forces associated with bursty bulk flows in Earth's magnetotail

Karlsson

Hamrin

Nilsson

et al. 2015

Geophysical Research Letters

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We present the first direct measurements of magnetic forces acting on bursty bulk flow plasma in the magnetotail. The magnetic forces are determined using Cluster multispacecraft measurements. We analyze 67 bursty bulk flow (BBF) events and show that the curvature part of the magnetic force is consistently positive, acting to accelerate the plasma toward Earth between approximately 10 and 20 RE geocentrical distances, while the magnetic field pressure gradient increasingly brakes the plasma as it moves toward Earth. The net result is that the magnetic force accelerates the plasma at distances greater than approximately 14 RE, while it acts to decelerate it within that distance. The magnetic force, together with the thermal pressure gradient force, will determine the dynamics of the BBFs as they propagate toward the near‐Earth tail region. The determination of the former provides an important clue to the ultimate fate of BBFs in the inner magnetosphere.

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Statistical analysis of dipolarizations using spacecraft closely separated along Z in the near‐Earth magnetotail

Cited by 10 publications

References 25 publications

On the current sheets surrounding dipolarizing flux bundles in the magnetotail: The case for wedgelets

On the current sheets surrounding dipolarizing flux bundles in the magnetotail: The case for wedgelets

Dipolarizing flux bundles in the cis‐geosynchronous magnetosphere: Relationship between electric fields and energetic particle injections

Magnetic forces associated with bursty bulk flows in Earth's magnetotail

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