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| Titel |
The dayside ultraviolet aurora and convection responses to a southward turning of the interplanetary magnetic field |
| VerfasserIn |
K. A. McWilliams, T. K. Yeoman, J. B. Sigwarth, L. A. Frank, M. Brittnacher |
| 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 ; 19, no. 7 ; Nr. 19, no. 7, S.707-721 |
| Datensatznummer |
250014283
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| Publikation (Nr.) |
 copernicus.org/angeo-19-707-2001.pdf |
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| Zusammenfassung |
We examine the
large-scale ultraviolet aurora and convection responses to a series of flux
transfer events that immediately followed a sharp and isolated southward
turning of the IMF. During the interval of interest, SuperDARN was monitoring
the plasma convection in the dayside northern ionosphere, while the VIS Earth
Camera and the Far Ul-traviolet Imager (UVI) were monitoring the northern
hemisphere’s ultraviolet aurora. Reconnection signatures were seen in the
SuperDARN HF radar data in the postnoon sector following a sharp southward
turning of the IMF. The presence of flux transfer events is supported by
measurements of a classic dispersed ion signature in the low-altitude cusp from
the DMSP spacecraft. Subsequent to the onset of reconnection, the postnoon
convection and ultraviolet aurora expanded in concert, reaching 18 MLT in half
an hour. The auroral oval was found to move equatorward at the convection speed
in the 16–18 MLT sector, implying that it was related directly to an adiaroic
magnetospheric boundary. In the present study, we have estimated the
field-aligned current response to magnetic reconnection in terms of the
vorticity of the ionospheric plasma convection velocity. The convection
velocities were obtained using two methods: (a) direct reconstruction of the
full vector velocities from bistatic measurements of the convection by the
SuperDARN HF radars in a relatively small region of the auroral zone, and (b)
from global-scale spherical harmonic fits to the SuperDARN velocities deduced
from the map potential model. Regions of high vorticity, which were predicted
to be an estimate of a component of the total field-aligned current, agree
extremely well with the images of the dayside UV aurora, indicating that, in
this case, the plasma vorticity is an excellent estimator of the morphology of
dayside field-aligned currents (FACs). The morphology of the aurora and
ionospheric electric field in the postnoon sector supports the existence of a
dayside current wedge induced in response to dayside reconnection.
Key words. Magnetospheric physics (auroral
phenomena; magnetosphere-ionosphere interactions; solar wind magne-tosphere
interactions) |
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