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- ELPHINSTONE, RD, et al.
(författare)
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OBSERVATIONS IN THE VICINITY OF SUBSTORM ONSET - IMPLICATIONS FOR THE SUBSTORM PROCESS
- 1995
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. - 0148-0227. ; 100:A5, s. 7937-7969
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Multi-instrument data sets from the ground and satellites at both low and high altitude have provided new results concerning substorm onset and its source region in the magnetosphere. Twenty-six out of 37 substorm onset events showed evidence of azimuthal
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- Marklund, Göran, et al.
(författare)
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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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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96:A6, s. 9567-9578
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Tidskriftsartikel (refereegranskat)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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- Ohtani, S, et al.
(författare)
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4 Large-scale field-aligned current systems in the dayside high-latitude region
- 1995
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 100, s. 137-153
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Tidskriftsartikel (refereegranskat)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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