How does the U-shaped potential close above the acceleration region? A study using Polar data
We present a statistical study of Polar electric field observations using auroral oval passes over Scandinavia above the acceleration region. We are especially interested in seeing whether we can find large perpendicular electric fields associated with an upward extended classical U-shaped poten...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
1999-10-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/17/1276/1999/angeo-17-1276-1999.pdf |
| Summary: | We present a statistical study of Polar
electric field observations using auroral oval passes over Scandinavia above the
acceleration region. We are especially interested in seeing whether we can find
large perpendicular electric fields associated with an upward extended classical
U-shaped potential drop for these passes, during which Polar is in the northern
hemisphere usually at about 4 <i>R<sub>E</sub></i> altitude. We also use Polar
magnetic field data to infer the existence of a field-aligned current (FAC) and
conjugate ground-based magnetometers (the IMAGE magnetometer network) to check
whether the event is substorm-related or not. We find several events with a FAC
but only weak perpendicular electric fields at Polar. In those rare cases where
the Polar electric field was large, its direction was mostly found to be
incompatible with the U-shaped potential model, or it was associated with
disturbed conditions (substorms), where one cannot easily distinguish between
inductive and static perpendicular electric fields. We found only two cases
which are compatible with the upward extended U-shaped potential picture, and
even in those cases the potential value is quite small (1-2 kV). To check the
validity of the analysis method we also estimate the perpendicular electric
field on the southern hemisphere, where Polar flies within or below the
acceleration region, and we found a large number of inverted-V-type signatures
as expected from previous studies. To explain the lack of perpendicular electric
fields at high altitudes we suggest an O-shaped potential model instead of the
U-shaped one.<br><br><b>Key words. </b>Ionosphere (particle acceleration) ·
Magnetospheric physics (auroral phenomena; magnetosphere · ionosphere
interactions) |
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| ISSN: | 0992-7689 1432-0576 |