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| Titel |
Observational study of generation conditions of substorm-associated low-frequency AKR emissions |
| VerfasserIn |
A. Olsson, P. Janhunen  , J. Hanasz, M. Mogilevsky, S. Perraut, J. D. Menietti |
| 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 ; 22, no. 10 ; Nr. 22, no. 10 (2004-11-03), S.3571-3582 |
| Datensatznummer |
250015032
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| Publikation (Nr.) |
 copernicus.org/angeo-22-3571-2004.pdf |
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| Zusammenfassung |
| It has lately been shown that low-frequency bursts of auroral kilometric
radiation (AKR) are nearly exclusively associated with substorm
expansion phases. Here we study low-frequency AKR using Polar PWI and
Interball POLRAD instruments to constrain its possible generation
mechanisms. We find that there are more low-frequency AKR emission
events during wintertime and equinoxes than during
summertime. The dot-AKR emission radial distance range coincides well with the region
where the deepest density cavities are seen statistically during Kp>2.
We suggest that the dot-AKR emissions originate in the deepest
density cavities during substorm onsets. The mechanism for generating
dot-AKR is possibly strong Alfvén waves entering the cavity from the
magnetosphere and changing their character to more inertial, which
causes the Alfvén wave associated parallel electric field to
increase. This field may locally accelerate electrons inside the
cavity enough to produce low-frequency AKR emission. We use
Interball IESP low-frequency wave data to verify that in about half of
the cases the dot-AKR is accompanied by low-frequency wave activity
containing a magnetic component, i.e. probably inertial Alfvén waves. Because of the observational
geometry, this result is consistent with the idea that inertial Alfvén
waves might always be present in the source region when
dot-AKR is generated. The paper illustrates once more the importance
of radio emissions as a powerful remote diagnostic tool of auroral processes,
which is not only relevant for the Earth's magnetosphere but may be
relevant in the future in studying extrasolar planets. |
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