Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study
A case study of SuperDARN observations of Pc5 Alfvén ULF wave activity generated in the immediate aftermath of a modest-intensity substorm expansion phase onset is presented. Observations from the Hankasalmi radar reveal that the wave had a period of 580 s and was characterized by an intermediate...
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2010-08-01
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Series: | Annales Geophysicae |
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doaj-bf8cc66b15a24b3d8176f85279cb51482020-11-24T23:41:36ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762010-08-01281499150910.5194/angeo-28-1499-2010Intermediate-<I>m</I> ULF waves generated by substorm injection: a case studyT. K. Yeoman0D. Yu. Klimushkin1P. N. Mager2Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKInstitute of Solar-Terrestrial Physics, Irkutsk, P.O. Box 291, 664033, RussiaInstitute of Solar-Terrestrial Physics, Irkutsk, P.O. Box 291, 664033, RussiaA case study of SuperDARN observations of Pc5 Alfvén ULF wave activity generated in the immediate aftermath of a modest-intensity substorm expansion phase onset is presented. Observations from the Hankasalmi radar reveal that the wave had a period of 580 s and was characterized by an intermediate azimuthal wave number (<I>m</I>=13), with an eastwards phase propagation. It had a significant poloidal component and a rapid equatorward phase propagation (~62° per degree of latitude). The total equatorward phase variation over the wave signatures visible in the radar field-of-view exceeded the 180° associated with field line resonances. The wave activity is interpreted as being stimulated by recently-injected energetic particles. Specifically the wave is thought to arise from an eastward drifting cloud of energetic electrons in a similar fashion to recent theoretical suggestions (Mager and Klimushkin, 2008; Zolotukhina et al., 2008; Mager et al., 2009). The azimuthal wave number <I>m</I> is determined by the wave eigenfrequency and the drift velocity of the source particle population. To create such an intermediate-<I>m</I> wave, the injected particles must have rather high energies for a given L-shell, in comparison to previous observations of wave events with equatorward polarization. The wave period is somewhat longer than previous observations of equatorward-propagating events. This may well be a consequence of the wave occurring very shortly after the substorm expansion, on stretched near-midnight field lines characterised by longer eigenfrequencies than those involved in previous observations.https://www.ann-geophys.net/28/1499/2010/angeo-28-1499-2010.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
T. K. Yeoman D. Yu. Klimushkin P. N. Mager |
spellingShingle |
T. K. Yeoman D. Yu. Klimushkin P. N. Mager Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study Annales Geophysicae |
author_facet |
T. K. Yeoman D. Yu. Klimushkin P. N. Mager |
author_sort |
T. K. Yeoman |
title |
Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study |
title_short |
Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study |
title_full |
Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study |
title_fullStr |
Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study |
title_full_unstemmed |
Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study |
title_sort |
intermediate-<i>m</i> ulf waves generated by substorm injection: a case study |
publisher |
Copernicus Publications |
series |
Annales Geophysicae |
issn |
0992-7689 1432-0576 |
publishDate |
2010-08-01 |
description |
A case study of SuperDARN observations of Pc5 Alfvén ULF wave activity
generated in the immediate aftermath of a modest-intensity substorm expansion
phase onset is presented. Observations from the Hankasalmi radar reveal that
the wave had a period of 580 s and was characterized by an intermediate
azimuthal wave number (<I>m</I>=13), with an eastwards phase propagation. It had a
significant poloidal component and a rapid equatorward phase propagation
(~62° per degree of latitude). The total equatorward phase
variation over the wave signatures visible in the radar field-of-view
exceeded the 180° associated with field line resonances. The wave
activity is interpreted as being stimulated by recently-injected energetic
particles. Specifically the wave is thought to arise from an eastward
drifting cloud of energetic electrons in a similar fashion to recent
theoretical suggestions (Mager and Klimushkin, 2008; Zolotukhina
et al., 2008; Mager et al., 2009). The
azimuthal wave number <I>m</I> is determined by the wave eigenfrequency and the
drift velocity of the source particle population. To create such an
intermediate-<I>m</I> wave, the injected particles must have rather high energies
for a given L-shell, in comparison to previous observations of wave
events with equatorward polarization. The wave period is somewhat longer than
previous observations of equatorward-propagating events. This may well be a
consequence of the wave occurring very shortly after the substorm expansion,
on stretched near-midnight field lines characterised by longer
eigenfrequencies than those involved in previous observations. |
url |
https://www.ann-geophys.net/28/1499/2010/angeo-28-1499-2010.pdf |
work_keys_str_mv |
AT tkyeoman intermediateimiulfwavesgeneratedbysubstorminjectionacasestudy AT dyuklimushkin intermediateimiulfwavesgeneratedbysubstorminjectionacasestudy AT pnmager intermediateimiulfwavesgeneratedbysubstorminjectionacasestudy |
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