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- Ohtani, S, et al.
(författare)
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Response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field
- 1997
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - 0148-0227. ; 102:A10, s. 22247-22260
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Tidskriftsartikel (refereegranskat)abstract
- The response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field (IMF) is examined with multi-instrument data from the Viking and DMSP-F7 satellites as well as ground magnetometer data. The event selected, which occurred on October 5, 1986, was previously identified as a high-latitude dayside form by Murphree and Elphinstone [1988]. IMF B-Y was positive during most of the Viking auroral UV observation, whereas IMF B-Z made a transient southward excursion, followed by a sharp increase to +8 nT. The results are summarized as follows: (1) There were two auroral belts extending westward from the early afternoon sector. The equatorward belt was persistent throughout the event and was embedded in the CPS/BPS precipitation region, whereas the poleward belt was in the open field line region and was associated with northward IMF B-Z. (2) A new auroral spot emerged in the afternoon sector just poleward of the previously active region, delayed 10 min from the sudden increase in IMF B-Z. This time lag is ascribed to the travel time of the new IMF orientation from the subsolar point to a solar wind-magnetosphere interaction site tailward of the dayside cusp, as well as to the response time of the dayside auroral acceleration process. (3) The new auroral activity expanded both eastward and westward during the first few minutes and then expanded primarily westward across the noon meridian, forming the poleward belt. The speed of the westward extension in the second phase was comparable to the speed of the ionospheric convection. (4) The dayside auroral process has a finite decay constant, which is inferred to be at least 10 min. (5) The response time of the midday ionospheric convection to IMF variations is estimated to be a few to several minutes.
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- Ohtani, S, et al.
(författare)
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Simultaneous prenoon and postnoon observations of 3 field-aligned current systems from Viking and DMSP F7
- 1995
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 100:A1, s. 119-136
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Tidskriftsartikel (refereegranskat)abstract
- The spatial structure of dayside large-scale field-aligned current (FAG) systems is examined by using Viking and DMSP-F7 data. We focus on four events in which the satellites simultaneously observed postnoon and prenoon three FAC systems: the region 2, the region 1, and the mantle (referred to as midday region 0) systems, from equatorward to poleward. These events provide the most solid evidence to date that the midday region 0 system is a separate and unique FAC system, and is not an extension of the region 1 system from other local times. The events are examined comprehensively by making use of a multi-instrument data set, which includes magnetic field, particle flux, electric field, auroral UV image data from the satellites, and the Sondrestrom convection data. The results are summarized as follows: (1) Region 2 currents flow mostly in the CPS precipitation region, often overlapping with the BPS at their poleward edge. (2) The region 1 system is located in the core part of the auroral oval and is confined in a relatively narrow range in latitude which includes the convection reversal. The low-latitude boundary layer, possibly including the outer part of the plasma sheet, and the external cusp are the major source regions of dayside region 1 currents. (3) Midday region 0 currents flow on open field lines and are collocated with the shear of antisunward convection flows with velocities decreasing poleward. On the basis of these results we support the view that both prenoon and postnoon current systems consist of the three-sheet structure when the distortion of the convection pattern associated with interplanetary magnetic field (IMF) B-y is small and both morningside and eveningside convection cells are crescent-shaped. We also propose that the midday region 0 and a part of the region 1 systems are closely coupled to the same source.
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