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| Titel |
Dual HF radar study of the subauroral polarization stream |
| VerfasserIn |
R. A. Makarevich, P. L. Dyson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 25, no. 12 ; Nr. 25, no. 12 (2008-01-02), S.2579-2591 |
| Datensatznummer |
250015964
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2579-2007.pdf |
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| Zusammenfassung |
| The dual HF radars comprising the Tasman International Geophysical Environment Radar (TIGER) system often observe localized high-velocity F-region
plasma flows (≥1500 m/s) in the midnight sector (20:00–02:00 MLT) at magnetic latitudes as low as Λ=60° S. The flow channels exhibit
large variability in the latitudinal extent and electric field strength, and are similar to the subauroral polarization stream or SAPS, a plasma
convection feature thought to be related to the polarization electric field due to the charge separation during substorm and storm development. In
this study, the 2-D plasma drift velocity within the channel is derived for each of the two TIGER radars from the maximum velocities measured
in all 16 radar beams within the latitudinally narrow channel, and the time variation of the subauroral electric field is examined near substorm
onset. It is demonstrated that the flow channel often does not have a clear onset, rather it manifests differently in different phases of its
evolution and can persist for at least two substorm cycles. During the growth phase the electric fields within the flow channel are difficult to
distinguish from those of the background auroral convection but they start to increase near substorm onset and peak during the recovery phase, in
contrast to what has been reported previously for auroral convection which peaks just before the substorm onset and falls sharply at the substorm
onset. The response times to substorm onset range from −5 to +40 min and show some dependence on the substorm location with longer delays observed
for substorms eastward of the radars' viewing area. The propagation velocity of the high-velocity region is also investigated by comparing the
observations from the two closely-spaced TIGER radars. The observations are consistent with the notion that the polarization electric field is
established with the energetic ions drifting westward and equatorward from the initial substorm injection. The ion injection front can precede that
of the electrons and hence substorm onset resulting in a negative response time of a few minutes. |
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