On the profile of intense high-altitude auroral electric fields at magnetospheric boundaries

Johansson, Tommy; Marklund, Göran; Karlsson, Tomas; Liléo, S.; Lindqvist, Per‐Arne; Marchaudon, A.; Nilsson, Hans; Fazakerley, A. N.

doi:10.5194/angeo-24-1713-2006

Cited by 22 publications

(51 citation statements)

References 32 publications

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“…As shown by Johansson et al (2006), quasi-static auroral E-field structures are closely related to plasma boundaries. It is generally believed that plasma shear flows at magnetospheric boundaries within a highly conductive plasma environment lead to magnetic stress that causes field-aligned currents (FACs).…”

Section: Possible Connection Between Discrete Arcs and Plasma Convectionmentioning

confidence: 98%

“…Note, that several of the events analyzed in Johansson et al (2006) have been investigated in detail within other contexts by Johansson et al (2004), Figueiredo et al (2005), and Marklund et al (2007). The dataset presented in Johansson et al (2006) is a subset from the dataset used in the large statistical studies by where all E-field events above 150 mV/m have been covered. Thus, the results from these studies are directly applicable to our work.…”

Section: Data Selectionmentioning

confidence: 99%

“…This concerns a few E-field peaks appearing near noon. The study of Johansson et al (2006) also contains a few well-defined E-field peak events with magnitudes below 500 mV/m. In the present study, these cases have been excluded.…”

Section: Data Selectionmentioning

confidence: 99%

“…The events used in this work are taken from a statistical study of intense E-fields by Johansson et al (2006), based on Efield measurements from the EFW instruments onboard the Cluster satellites (Gustavsson et al, 1997). In their study, the E-field is mapped along the geomagnetic field lines to 100 km height by using the dipole field approximation, to be able to compare measurements taken at different altitudes.…”

Section: Data Selectionmentioning

confidence: 99%

“…In their study, the E-field is mapped along the geomagnetic field lines to 100 km height by using the dipole field approximation, to be able to compare measurements taken at different altitudes. Johansson et al's (2006) dataset contains all intense E-field events appearing between January 2001 and September 2003 at geocentric distances between 4 and 7 R E with mapped Efield magnitudes in the range of 500-1000 mV/m that show clear bipolar or monopolar quasi-static E-field structures. The latter requirement has been fulfilled with help of manual inspection of the E-field data.…”

Section: Data Selectionmentioning

confidence: 99%

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Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection

et al. 2008

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Abstract. The role of intense high-altitude electric field (Efield) peaks for large-scale plasma convection is investigated with the help of Cluster E-field, B-field and density data. The study covers 32 E-field events between 4 and 7 R E geocentric distance, with E-field magnitudes in the range 500-1000 mV/m when mapped to ionospheric altitude. We focus on E-field structures above the ionosphere that are typically coupled to discrete auroral arcs and their return current region. Connected to such E-field peaks are rapid plasma flows directed along the discrete arcs in opposite directions on each side of the arc.Nearly all the E-field events occur during active times. A strong dependence on different substorm phases is found: a majority of intense E-field events appearing during substorm expansion or maximum phase are located on the nightside oval, while most recovery events occur on the dusk-todayside part of the oval. For most expansion and maximum phase cases, the average background plasma flow is in the sunward direction. For a majority of recovery events, the flow is in the anti-sunward direction.The net plasma flux connected to a strong E-field peak is in two thirds of the cases in the same direction as the background plasma flow. However, in only one third of the cases the strong flux caused by an E-field peak makes an important contribution to the plasma transport within the boundary plasma sheet. For a majority of events, the area covered by rapid plasma flows above discrete arcs is too small to have Correspondence to: A. Kullen (kullen@irfu.se) an effect on the global convection. This questions the role of discrete auroral arcs as major driver of plasma convection.

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Section: Possible Connection Between Discrete Arcs and Plasma Convectionmentioning

confidence: 98%

Section: Data Selectionmentioning

confidence: 99%

Section: Data Selectionmentioning

confidence: 99%

Section: Data Selectionmentioning

confidence: 99%

Section: Data Selectionmentioning

confidence: 99%

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Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection

et al. 2008

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Inverted‐V and low‐energy broadband electron acceleration features of multiple auroras within a large‐scale surge

Marklund

Karlsson

et al. 2013

JGR Space Physics

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[1] Results are presented from a Cluster C2 satellite crossing through the acceleration region of multiple auroral structures within a large-scale surge, simultaneously monitored by DMSP F17 imager data. The magnetic and electric field data are consistent with the auroral distribution at large and medium scales. We identify the quasi-static acceleration above and below C2 orbit by downgoing inverted-V electrons and parallel electric potential drops, respectively. In the poleward surge region, within or adjacent to the inverted-V arcs, intense low-energy (broadband) electron fluxes are seen as well as a rough equality between ΔE/ΔB and the Alfvén velocity, suggesting that these are of Alfvénic origin. The most poleward and equatorward auroral structure is found to be Alfvénic and quasi-static, respectively. In between, the structures are of mixed origin. We estimate the relative role of the acceleration processes by the contributions to the downward electron energy flux by electrons above and below 1.62 keV. Although these are local estimates, they should be representative also below Cluster altitude, except for two regions of intense downward Poynting flux, the power of which will be dissipated at lower altitudes and increasing the Alfvénic contribution. This is also supported by intense fluxes of low-energy, broadband, upgoing electrons observed within these regions. Otherwise, the inverted-V contribution dominates for most of the auroral structures observed by Cluster. The Alfvénic contribution to the mixed arc emissions is to extend these to higher altitudes, as shown by numerical simulation results.

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Electric Fields and Plasma Processes in the Auroral Downward Current Region, Below, Within, and Above the Acceleration Region

Marklund

2008

Space Sci Rev

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The downward field-aligned current region plays an active role in magnetosphereionosphere coupling processes associated with aurora. A quasi-static electric field structure with a downward parallel electric field forms at altitudes between 800 km and 5000 km, accelerating ionospheric electrons upward, away from the auroral ionosphere. A wealth of related phenomena, including energetic ion conics, electron solitary waves, low-frequency wave activity, and plasma density cavities occur in this region, which also acts as a source region for VLF saucers. Results are presented from sounding rockets and satellites, such as Freja, FAST, Viking, and Cluster, to illustrate the characteristics of the electric fields and related parameters, at altitudes below, within, and above the acceleration region. Special emphasis will be on the high-altitude characteristics and dynamics of quasi-static electric field structures observed by Cluster. These structures, which extend up to altitudes of at least 4-5 Earth radii, appear commonly as monopolar or bipolar electric fields. The former are found to occur at sharp boundaries, such as the polar cap boundary whereas the bipolar fields occur at soft plasma boundaries within the plasma sheet. The temporal evolution of quasi-static electric field structures, as captured by the pearls-on-a-string configuration of the Cluster spacecraft indicates that the formation of the electric field structures and of ionospheric plasma density cavities are closely coupled processes. A related feature of the downward current often seen is a broadening of the current sheet with time, possibly related to the depletion process. Preliminary studies of the coupling of electric fields in the downward current region, show that small-scale structures appear to be decoupled from the ionosphere, similar to what has been found for the upward current region. However, exceptions are also found where small-scale electric fields couple perfectly between the ionosphere and Cluster altitudes. Recent FAST results indicate that the degree of coupling differs between sheet-like and curved structures, and that it is typically partial. The mapping depends on the current-voltage relationship in the downward current region, which is highly non-linear and still unclear, as to its specific form.G.T. Marklund ( ) Space and Plasma Physics,

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On the profile of intense high-altitude auroral electric fields at magnetospheric boundaries

Cited by 22 publications

References 32 publications

Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection

Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection

Inverted‐V and low‐energy broadband electron acceleration features of multiple auroras within a large‐scale surge

Electric Fields and Plasma Processes in the Auroral Downward Current Region, Below, Within, and Above the Acceleration Region

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