Characteristics of field-aligned currents near the auroral acceleration region: FAST observations

Peria, W. J.; Carlson, C. W.; Ergun, R. E.; McFadden, J. P.; Bonnell, J. W.; Elphic, R. C.; Strangeway, R. J.

doi:10.1029/gm118p0181

Cited by 23 publications

(37 citation statements)

References 17 publications

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“…Strong, significant correlations were only observed for events when the ionospheric foot point of the current sheet was illuminated and not when it was in Figure 2. (opposite) The complete set of 'Region I' currents determined from the Peria et al [2000] data set. (a) All individual Region I currents plotted as red '+' (green 'x') points corresponding to currents out of (into) the ionosphere; (b) the average of the Region I current density in each MLT-ILAT bin (for bins with more than 10 Region I current sheets).…”

Section: Discussionmentioning

confidence: 99%

“…The algorithm, utilized on approximately every tenth orbit from October 1996 through January 1998, examined the magnetic field perturbations for consistency with a steady fieldaligned current sheet. Details are given by Peria et al [2000]. The resulting database covers all local times, and altitudes from $300 to $4300 km.…”

Section: Data Sets and Methodologymentioning

confidence: 99%

“…Peria et al [2000] developed an automatic algorithm to identify field-aligned currents from the three-axis fluxgate magnetometer data. The algorithm, utilized on approximately every tenth orbit from October 1996 through January 1998, examined the magnetic field perturbations for consistency with a steady fieldaligned current sheet.…”

Section: Data Sets and Methodologymentioning

confidence: 99%

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Fast Auroral Snapshot observations of the dependence of dayside auroral field‐aligned currents on solar wind parameters and solar illumination

et al. 2003

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[1] The solar illumination dependence of solar wind-magnetosphere coupling has been studied by examining the dependence of auroral zone field-aligned currents on solar wind parameters. A database of Region I currents from $900 crossings of the auroral zone by Fast Auroral Snapshot (FAST) was parameterized by magnetic local time, invariant latitude, and whether the foot point was illuminated. The magnitudes of dayside currents ($200 events) were correlated with solar wind parameters using the technique of rank correlation. Very significant, strong correlation between dayside sunlit currents and solar wind parameters such as B t sin(q/2)v 2 and B t sin(q/2)P d 1/2 was observed, consistent with a reconnection source. There was no correlation with upstream parameters for dayside Region I currents when the ionospheric foot point was in darkness. This is the first experimental evidence showing that the correlation of dayside Region I currents to upstream parameters depends on ionospheric illumination. Both the strong dependence of the correlation on solar illumination (ionospheric conductivity) and the weakness of observed correlations, compared to those obtained in previous studies of the cross polar cap potential, may be interpreted to imply that the reconnection process is a voltage, rather than a current, source. However, several theoretical studies have suggested that reconnection does not act as either a pure voltage source or a current source. In addition, because the mapping of the field-aligned currents was not examined, the observed difference between the sunlit and dark events could be explained by current preferentially flowing in the hemisphere with the higher conductivity if the source were on closed field lines.

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Section: Discussionmentioning

confidence: 99%

Section: Data Sets and Methodologymentioning

confidence: 99%

Section: Data Sets and Methodologymentioning

confidence: 99%

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Fast Auroral Snapshot observations of the dependence of dayside auroral field‐aligned currents on solar wind parameters and solar illumination

et al. 2003

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“…In order to use this method correctly, strict selection schemes must be applied [Peria et al, 2000]. There must be other data supporting the assumption that the observed current is spatial and 'sheetlike'.…”

Section: Current Density Measurement Techniquesmentioning

confidence: 99%

“…Measurements from the FAST spacecraft include many observations of sheet currents where the current density as measured by the magnetometer is quantitatively consistent with the current carriers measured by the electron detectors [Peria et al, 2000, Carlson et al, 1998]. Observations of Alfvénic activity from Polar [Wygant et al, 2000;Keiling et al, 2001], Freja [Louarn et al, 1994], and rocket data [Knudsen et al, 1990[Knudsen et al, , 1992 include many examples of electric and magnetic field fluctuations which clearly satisfy conditions for Alfvén wave activity.…”

Section: Interpreting Magnetic Fluctuationsmentioning

confidence: 99%

Multipoint measurements of field‐aligned current density in the auroral zone

et al. 2003

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[1] In this paper we present the analysis and interpretation of a multipoint observation of magnetic field structures at the poleward edge of a premidnight auroral arc by the Enstrophy sounding rocket mission. Four Free-Flying Magnetometers (FFMs) employing autonomous nanospacecraft technology were deployed from the main payload during the flight, and multipoint magnetic field measurements were made. Signatures consistent with both spatial and temporal interpretations were found to be present when large fluctuations in B were seen at the edge of an arc as the rocket flew into the polar cap. Reasons for the interpretation of spatial or temporal features are given and supported by a simple model of multiple payloads crossing through several moving current sheets and a study of the fine structure of this auroral event using multipoint, correlative wavelet analysis to find velocities of structures at different scale sizes. We show that the direct measurement method of current density using multipoint measurement of magnetic fields gives us a different current density than what would be inferred from a single-point measurement and that the multipoint measurement also provides an inherent check on the validity of the measurement through a calculation of the divergence of the measured B.INDEX TERMS:

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The detailed spatial structure of field‐aligned currents comprising the substorm current wedge

et al. 2013

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[1] We present a comprehensive two-dimensional view of the field-aligned currents (FACs) during the late growth and expansion phases for three isolated substorms utilizing in situ observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment and from ground-based magnetometer and optical instrumentation from the Canadian Array for Realtime Investigations of Magnetic Activity and Time History of Events and Macroscale Interactions during Substorms ground-based arrays. We demonstrate that the structure of FACs formed during the expansion phase and associated with the substorm current wedge is significantly more complex than a simple equivalent line current model comprising a downward FAC in the east and upward FAC in the west. This two-dimensional view demonstrates that azimuthal bands of upward and downward FACs with periodic structuring in latitude form across midnight and can span up to 8 h of magnetic local time. However, when averaged over latitude, the overall longitudinal structure of the net FACs resembles the simpler equivalent line current description of the substorm current wedge (SCW). In addition, we demonstrate that the upward FAC elements of the structured SCW are spatially very well correlated with discrete aurora during the substorm expansion phase and that discrete changes in the FAC topology are observed in the late growth phase prior to auroral substorm expansion phase onset. These observations have important implications for determining how the magnetosphere and ionosphere couple during the late growth phase and expansion phase, as well as providing important constraints on the magnetospheric generator of the FACs comprising the SCW.

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Characteristics of field-aligned currents near the auroral acceleration region: FAST observations

Cited by 23 publications

References 17 publications

Fast Auroral Snapshot observations of the dependence of dayside auroral field‐aligned currents on solar wind parameters and solar illumination

Fast Auroral Snapshot observations of the dependence of dayside auroral field‐aligned currents on solar wind parameters and solar illumination

Multipoint measurements of field‐aligned current density in the auroral zone

The detailed spatial structure of field‐aligned currents comprising the substorm current wedge

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