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The statistical difference between bending arcs and regular polar arcs

The statistical difference between bending arcs and regular polar arcs
The statistical difference between bending arcs and regular polar arcs
In this work, the Polar UVI data set by Kullen et al. (2002) of 74 polar arcs is reinvestigated, focusing on bending arcs. Bending arcs are typically faint and form (depending on interplanetary magnetic field (IMF) By direction) on the dawnside or duskside oval with the tip of the arc splitting off the dayside oval. The tip subsequently moves into the polar cap in the antisunward direction, while the arc's nightside end remains attached to the oval, eventually becoming hook-shaped. Our investigation shows that bending arcs appear on the opposite oval side from and farther sunward than most regular polar arcs. They form during By-dominated IMF conditions: typically, the IMF clock angle increases from 60 to 90° about 20?min before the arc forms. Antisunward plasma flows from the oval into the polar cap just poleward of bending arcs are seen in Super Dual Auroral Radar Network data, indicating dayside reconnection. For regular polar arcs, recently reported characteristics are confirmed in contrast to bending arcs. This includes plasma flows along the nightside oval that originate close to the initial arc location and a significant delay in the correlation between IMF By and initial arc location. In our data set, the highest correlations are found with IMF By appearing at least 1–2?h before arc formation. In summary, bending arcs are distinctly different from regular arcs and cannot be explained by existing polar arc models. Instead, these results are consistent with the formation mechanism described in Carter et al. (2015), suggesting that bending arcs are caused by dayside reconnection.
2169-9380
10,443-10,465
Kullen, A.
9575b1dc-27c9-4367-b77a-045c1746ae39
Fear, R.C.
8755b9ed-c7dc-4cbb-ac9b-56235a0431ab
Milan, S.E.
4495fdee-b600-43e5-99f7-6193a849b7f5
Carter, J.A.
750f3f36-98fc-4729-acfe-60ded2bd23c1
Karlsson, T.
e55ac446-3a69-47b9-aeda-7645bc778a90
Kullen, A.
9575b1dc-27c9-4367-b77a-045c1746ae39
Fear, R.C.
8755b9ed-c7dc-4cbb-ac9b-56235a0431ab
Milan, S.E.
4495fdee-b600-43e5-99f7-6193a849b7f5
Carter, J.A.
750f3f36-98fc-4729-acfe-60ded2bd23c1
Karlsson, T.
e55ac446-3a69-47b9-aeda-7645bc778a90

Kullen, A., Fear, R.C., Milan, S.E., Carter, J.A. and Karlsson, T. (2015) The statistical difference between bending arcs and regular polar arcs Journal of Geophysical Research: Space Physics, 120, (12), 10,443-10,465.

Record type: Article

Abstract

In this work, the Polar UVI data set by Kullen et al. (2002) of 74 polar arcs is reinvestigated, focusing on bending arcs. Bending arcs are typically faint and form (depending on interplanetary magnetic field (IMF) By direction) on the dawnside or duskside oval with the tip of the arc splitting off the dayside oval. The tip subsequently moves into the polar cap in the antisunward direction, while the arc's nightside end remains attached to the oval, eventually becoming hook-shaped. Our investigation shows that bending arcs appear on the opposite oval side from and farther sunward than most regular polar arcs. They form during By-dominated IMF conditions: typically, the IMF clock angle increases from 60 to 90° about 20?min before the arc forms. Antisunward plasma flows from the oval into the polar cap just poleward of bending arcs are seen in Super Dual Auroral Radar Network data, indicating dayside reconnection. For regular polar arcs, recently reported characteristics are confirmed in contrast to bending arcs. This includes plasma flows along the nightside oval that originate close to the initial arc location and a significant delay in the correlation between IMF By and initial arc location. In our data set, the highest correlations are found with IMF By appearing at least 1–2?h before arc formation. In summary, bending arcs are distinctly different from regular arcs and cannot be explained by existing polar arc models. Instead, these results are consistent with the formation mechanism described in Carter et al. (2015), suggesting that bending arcs are caused by dayside reconnection.

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Accepted/In Press date: 17 November 2015
Published date: 18 December 2015
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 394181
URI: http://eprints.soton.ac.uk/id/eprint/394181
ISSN: 2169-9380
PURE UUID: 270afa49-3c8b-42d2-8d1f-0a84b2f3dac4
ORCID for R.C. Fear: ORCID iD orcid.org/0000-0003-0589-7147

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Date deposited: 12 May 2016 11:38
Last modified: 04 Oct 2017 01:40

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Contributors

Author: A. Kullen
Author: R.C. Fear ORCID iD
Author: S.E. Milan
Author: J.A. Carter
Author: T. Karlsson

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