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| Titel |
Auroral precipitation fading before and at substorm onset: ionospheric and geostationary signatures |
| VerfasserIn |
K. Kauristie, T. I. Pulkkinen, A. Huuskonen, R. J. Pellinen, H. J. Opgenoorth, D. N. Baker, A. Korth, M. Syrjäsuo |
| 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 ; 15, no. 8 ; Nr. 15, no. 8, S.967-983 |
| Datensatznummer |
250012905
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| Publikation (Nr.) |
 copernicus.org/angeo-15-967-1997.pdf |
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| Zusammenfassung |
| Rapid fading of auroral activity a few
minutes before substorm breakup has earlier been analyzed in case-studies. Here
we report on a study in which all-sky camera (ASC) and magnetic data over 3
years were examined to find breakups that were accompanied by a preceding
fading. To illustrate typical features of the fading effect we analyze three
events in detail and discuss seven other events to find the spatial and temporal
behavior of the fading and the global conditions favoring this phenomenon, which
is not associated with every breakup. In these ten events the precipitation
diminished typically for about 2 min and a local breakup followed after 2–3 min.
Usually the arc which broke up had faded earlier. Comparison with geostationary
electron flux recordings shows that in many cases the global onset had already
taken place when the fading was recorded at a different longitude. Thus fading
is not just a growth-phase phenomenon as often thought, but can also appear as a
precursor of the approaching auroral bulge. The AE index and solar-wind
data reveal that the fading has a tendency to take place during magnetically
disturbed conditions caused by continuous energy input from the solar wind.
Furthermore, while a widely recognized phenomenon, we have found that the fading
prior to breakup is not a very common feature in the spatio-temporal scale of
auroral ASC recordings. In many cases the deepness of the fading had a
longitudinal dependence, which leads to the suggestion that this phenomenon is
related to azimuthal gradients in the tail magnetic field and/or plasma
pressure. Possible scenarios causing fading both before and after the onset are
discussed based on a few previously presented theoretical auroral-arc models. |
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