| 1. |
- Cumnock, Judy, et al.
(författare)
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High-Latitude Ionospheric Convection Pattern During Steady Northward Interplanetary Magnetic Field
- 1995
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 100, s. 14537-14555
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Tidskriftsartikel (refereegranskat)abstract
- The DMSP F8 satellite’s coverage of Earth’s polar regions provides horizontal ion drift velocities along the dawn-dusk meridian at approximately 835 km altitude in each hemisphere during the similar to 100 min orbital period. We examine the ionospheric convection signatures observed by this spacecraft in the summer and winter hemispheres during periods when the interplanetary magnetic field (IMF) is directed northward for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass. These convection signatures can be readily categorized by the number of sunward and antisunward flow regions and by their potential distributions. Here we describe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward IMF conditions. In addition to IMF B-z, the influences on the convection pattern of the IMF B-z/\textbackslashB-y\textbackslash ratio, season, latitude, and solar wind velocity are all considered. The ratio B-z/\textbackslashB-y\textbackslash provides a first order organization of the signatures that occur on the dayside of the dawn-dusk meridian. Sunward flow at highest latitudes on the dayside of the dawn-dusk meridian is the dominant feature seen in the large-scale convection signature during steady northward IMF; however, sunward flow at highest latitudes does not imply the existence of a particular number of convection cells.
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| 2. |
- Ohtani, S, et al.
(författare)
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Altitudinal comparison of dayside field-aligned current signatures by viking and DMSP-F7 : Intermediate-scale field-aligned current systems
- 1996
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 101:A7, s. 15297-15310
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Tidskriftsartikel (refereegranskat)abstract
- Dayside large-scale and intermediate-scale field-aligned current (FAG) signatures are examined with multi-instrument measurements from Viking and DMSP-F7 at magnetic conjunctions. The present paper reports four such conjunction events, with an emphasis on an event that occurred on October 13, 1986. In these four events both Viking and DMSP-F7 crossed prenoon FAC systems approximately along meridians. The altitude of DMSP-F7 was 835 km, whereas that of Viking ranged from 8500 to 12,000 km. The electric to magnetic field ratio measured by Viking indicates that intermediate-scale FAC systems, as well as large-scale FAC systems, are often quasi-stationary, This is also supported by the comparison between the Viking and DMSP-F7 magnetic measurements. The only obvious exception is the equatorward part of the October 13 event, in which the Viking and DMSP-F7 measurements are better explained in terms of Alfven waves. In two other events the Viking signature projected to the DMSP-F7 altitude is significantly more structured than the DMSP-F7 signature, although the electric to magnetic field ratio observed by Viking suggests that the associated FACs were quasistationary. This apparent discrepancy is possibly ascribed to the fact that Viking stays longer in FAC systems and therefore has more chance to observe temporal changes in FACs. However, such temporal effects must operate longer than the Alfven transit time so that FAC systems become quasi-stationary. Although the generation mechanism(s) of intermediate-scale FAC systems remains an open question, possibilities include a localized shear of plasma convection and a localized merging between the solar wind and magnetospheric field lines.
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| 3. |
- 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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