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| Titel |
SABRE observations of structured ionospheric flows during substorm expansion phase onset |
| VerfasserIn |
E. G. Bradshaw, Mark Lester, T. B. Jones |
| 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 ; 12, no. 10/11 ; Nr. 12, no. 10/11, S.1027-1038 |
| Datensatznummer |
250010341
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| Publikation (Nr.) |
 copernicus.org/angeo-12-1027-1994.pdf |
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| Zusammenfassung |
| The irregularity velocity patterns observed
by the SABRE coherent radar at substorm expansion phase onset, which is
identified by magnetometer observations of Pi2 pulsations, are occasionally
highly structured. In all the examples of structured velocity patterns examined,
the SABRE viewing area is located at longitudes within the inferred substorm
current wedge. Three types of structured velocity regime are apparent depending
on the level of magnetic activity and the position of the radar viewing area
relative to the substorm enhanced currents and the Pi2 pulsation generation
region. Firstly, vortex-like velocity patterns are observed and these may be
caused by the field-aligned currents associated with the substorm current wedge.
Secondly, regions of equatorward velocity are also observed at times of substorm
expansion phase onset moving longitudinally across the SABRE viewing area. The
longitudinal movement is usually westward although an example of eastward motion
has been observed. The phase velocity of these regions of equatorward flow is
typically 1-3 km s-1. The observed equatorward velocities occur at
the poleward edge or poleward of the background convection velocities observed
by SABRE. These equatorward velocities may be related to the westward travelling
surge and to the expansion (eastwards as well as westwards) of the brightening
arc region at substorm onset. Thirdly, the flow rotates equatorward within the
field of view but does not then appear to move longitudinally. These equatorward
velocities may relate to the earthward surge of plasma from the magnetotail at
substorm onset. |
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