Plasma pressure generated auroral current system: A case study

Mende, S. B.; England, S.; Frey, H. U.

doi:10.1029/2012gl051211

Cited by 4 publications

(3 citation statements)

References 12 publications

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“…It may also be that the nature of the ionospheric conductance depends on the mechanism of the current wedge formation. It has been widely known that the current wedge is expected to be formed through magnetotail pressure gradients [e.g., Shiokawa et al ., , ; Birn et al ., ; Xing et al ., ; Mende et al ., ] and by polarization currents ( Paschmann et al . ; Birn et al .…”

Section: Discussionmentioning

confidence: 99%

Ionospheric response to oscillatory flow braking in the magnetotail

et al. 2013

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[1] We study the ionospheric response to oscillatory braking of bursty bulk flow observed by THEMIS on 17 March 2008 between 10:22 and 10:36 UT. By calculating different current components generated in the plasma sheet and correlating the space and ground observations, we discriminate the ionospheric current relevant to the large-scale substorm wedge currents produced by the general reconfiguration of the magnetotail pressure gradient from the currents that appeared as a result of the flow oscillation. While the former currents are large and quasi-stable, the latter (oscillating) currents are substantially (2-3 times) weaker and flow in opposite directions during earthward and tailward flow bursts. The oscillating currents include the polarization current and the current generated by the oscillating part of the pressure gradient. The two oscillating currents appear to produce modulation of the ionospheric currents (with about 2.5 min period) that was seen as Pi2 pulsations in the ground magnetometer observations. Our estimates of the ionospheric conductance suggest that the damping of the plasma sheet flow oscillation is due to heating the ionosphere through Pedersen currents. We also found that the all-sky imager at Fort Yukon observed four auroral forms during the first two periods of the oscillatory flow braking: two auroral forms related to the earthward plasma sheet flows and the other two auroral forms related to the tailward rebounds of the earthward flow. The auroral forms evolve in accordance with the appearance and motion of the upward field-aligned current spot of the modulated part of the ionospheric field-aligned current.

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Section: Discussionmentioning

confidence: 99%

Ionospheric response to oscillatory flow braking in the magnetotail

et al. 2013

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“…Further analysis indicates that field‐aligned current (FAC) flows out of the magnetosphere if surfaces of constant pressure are not aligned with magnetic shells or if flow shear exists [ Vasyliunas ]. While the connection between the preexisting auroral arc (PAA) and magnetospheric pressure gradients has been discussed [e.g., Mende et al , ], no studies have looked at the relationship between flow shear and the source of the PAA before substorm onset. Therefore, it is the objective of this study to investigate whether a flow shear is related to the PAA.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric flow shear associated with the preexisting auroral arc: A statistical study from the FAST spacecraft data

et al. 2015

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An auroral substorm is a disturbance in the magnetosphere that releases energy stored in the magnetotail into the high-latitude ionosphere. By definition, an auroral substorm commences when a discrete auroral arc brightens and subsequently expands poleward and azimuthally. The arc that brightens is usually the most equatorward of several auroral arcs that remain quiescent for~5 to~60 min before the breakup commences. This arc is often referred to as the "preexisting auroral arc (PAA)" or the "growth-phase arc." In this study, we use FAST measurements to establish the statistics of flow patterns near PAAs in the ionosphere. We find that flow shear is present in the vicinity of a preexisting arc. When a PAA appears in the evening sector, enhanced westward flow develops equatorward of the arc, whereas when a PAA appears in the morning sector, enhanced eastward flow develops poleward of the arc. We benchmark locations of the PAAs relative to large-scale field-aligned currents (FACs) and convective flows in the ionosphere, finding that the arc forms in the upward current region within~1°of the Region 1/Region 2 boundary in all local time sectors from 20 MLT to 03 MLT. We also find that near midnight in the Harang region, most of the PAAs lie within 0.5°poleward of the low-latitude Region 1/Region 2 currents boundary and sit between the westward and eastward flow peak but equatorward of the flow reversal point. Finally, we examine arc-associated electrodynamics and find that the FAC of the PAA is mainly closed by the north-south Pedersen current in the ionosphere.

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“…A (smooth) latitudinal dependence for Φ is perhaps to be expected due to differences in field line length and convergence (mirror ratio), magnetic field angle of incidence with the ionosphere, density altitude profiles, etc. There is an indication that azimuthal pressure gradient driving of meridional currents perpendicular to the magnetic field in the dawn and dusk closed field line regions is more effective at higher latitudes [e.g., Mende et al ., ], and it is possible that this is related to the phenomena reported herein, but to our knowledge no theoretical treatment of Φ on latitude has been developed. We will put our findings in the context of current physical understanding in this section, paying most attention to what is likely the most important result—the existence of the multiple physical regimes and the ramifications to the current‐voltage relationship.…”

Section: Discussionmentioning

confidence: 96%

A FAST study of quasi‐static structure (“Inverted‐V”) potential drops and their latitudinal dependence in the premidnight sector and ramifications for the current‐voltage relationship

2013

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[1] Utilizing FAST satellite electron measurements, we present the first reported investigation of the dependency on latitude of quasi-static structure ("inverted-V") potential drop magnitude (Φ). A trend of lower Φ at lower latitudes in the premidnight sector on field lines with dark foot points was observed. This trend is supported both statistically and in individual satellite crossings. The existence of two distinct peaks in occurrence probability for Φ was also observed: one between~2 kV and 10 kV and the other at somewhat less than 1 kV. The relative occurrence of structures with Φ in the higher (>2 kV) peak is significantly reduced with decreasing latitude. This partially accounts for the statistical trend of lower potential drop magnitudes at lower latitudes. The two Φ occurrence frequency peaks correspond to two different regimes (one with eΦ/kT e~o r > 1 and one with eΦ/kT e < 1). In the lower Φ (<1 kV, eΦ/kT e <~1) regime which constitutes the vast majority of midlatitude events, these results are consistent with a voltage source configuration or more complex current-voltage relation where source electron density rather than Φ is most directly controlled by the field-aligned current density. These observations and their ramifications represent a significant step forward in the understanding of field-aligned currents, auroral acceleration, and magnetospheric-ionospheric coupling.Citation: Dombeck, J., C. Cattell, and J. McFadden (2013), A FAST study of quasi-static structure ("Inverted-V") potential drops and their latitudinal dependence in the premidnight sector and ramifications for the current-voltage relationship,

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Plasma pressure generated auroral current system: A case study

Cited by 4 publications

References 12 publications

Ionospheric response to oscillatory flow braking in the magnetotail

Ionospheric response to oscillatory flow braking in the magnetotail

Ionospheric flow shear associated with the preexisting auroral arc: A statistical study from the FAST spacecraft data

A FAST study of quasi‐static structure (“Inverted‐V”) potential drops and their latitudinal dependence in the premidnight sector and ramifications for the current‐voltage relationship

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