| 1. |
- Aad, G, et al.
(author)
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- 2015
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swepub:Mat__t
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| 2. |
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| 3. |
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| 4. |
- Lühr, H, et al.
(author)
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Fine-structure of field-aligned currente sheets deduced from spacecraft and ground-based observations - initial Freja results
- 1994
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 21, s. 1883-1886
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Journal article (peer-reviewed)abstract
- Due to its special orbit-over large segments tangential to the auroral oval and at altitudes around 1600 km-FREJA provides measurements from a sparsely sampled region. Here we will introduce initial results from the magnetic field experiment. For one event occurring about an hour after midnight we investigate the fine structure of the field-aligned currents associated with a westward electrojet. From simultaneous ground-based observations we deduce the orientation and the spatial and temporal variations of the electrojet. Space-borne magnetic field measurements provide estimates of the field-aligned current density. We deduce a lower limit of 1.75 km for the thickness of field-aligned current filaments. The comparison between electric and magnetic field recordings on FREJA suggests a poor correlation of these quantities for this event.
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| 5. |
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| 6. |
- Marklund, Göran, et al.
(author)
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On the electrodynamic state of the auroral ionosphere during northward interplanetary magnetic field - a transpolar arc case study
- 1991
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96:A6, s. 9567-9578
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Journal article (peer-reviewed)abstract
- The ionospheric electrodynamical state has been reconstructed for a transpolar arc event during northward interplanetary magnetic field conditions. An extensive set of observations by Viking and other satellites and by ground-based radars has been used to provide realistic model input data or to verify the modeling results. The resulting convection pattern is found to be consistent with the Viking electric field and intimately linked to the prevalent auroral distribution. It is characterized by a large evening cell, well extended across noon and split up by two separated potential minima, and a minor crescent-shaped morning cell. The convection signatures are found to vary a lot along the transpolar arc depending on the relative role of the arc-associated convection and the ambient convection. The transpolar arc is generally embedded in antisunward convective flow except near the connection points with the auroral oval, where sunward flow exists in localized regions.
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| 7. |
- Ohtani, S, et al.
(author)
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4 Large-scale field-aligned current systems in the dayside high-latitude region
- 1995
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 100, s. 137-153
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Journal article (peer-reviewed)abstract
- A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and DMSP-F7 crossings of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the CPS precipitation region, often overlapping with the BPS at its poleward edge, and is interpreted as a region 2 current. The pair of downward and upward FACs in the middle of the structure are collocated with structured electron precipitation. The precipitation of high-energy (>1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simultaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region 0) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B-Y, We discuss the FAC structure in terms of three types of convection cells: the merging, viscous, and lobe cells. During strongly negative IMF B-Y two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitudinal overlap of midday and morning FAC systems. We suggest that the four-current sheet structure is common in a certain prenoon local time sector during strongly negative IMF B-Y.
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| 8. |
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| 9. |
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| 10. |
- Wahlund, JE, et al.
(author)
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Broadband ELF plasma emission during auroral energization 1. Slow ion acoustic waves
- 1998
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In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. ; 103:A3, s. 4343-4375
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Journal article (other academic/artistic)abstract
- High-resolution measurements by the Freja spacecraft of broadband extremely low frequency (BB-ELF) emission from de up to the lower hybrid frequency (a few kHz) are reported from regions of transverse ion acceleration (TAI) and broad-energy suprathermal e
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