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| Titel |
Strange VLF bursts in northern Scandinavia: case study of the afternoon "mushroom-like" hiss on 8 December 2013 |
| VerfasserIn |
J. Manninen, N. G. Kleimenova, A. Kozlovsky, I. A. Kornilov, L. I. Gromova, Y. V. Fedorenko, T. Turunen |
| 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 ; 33, no. 8 ; Nr. 33, no. 8 (2015-08-12), S.991-995 |
| Datensatznummer |
250121232
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| Publikation (Nr.) |
 copernicus.org/angeo-33-991-2015.pdf |
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| Zusammenfassung |
| We investigate a non-typical very low frequency (VLF) 1–4 kHz hiss
representing a sequence of separated noise bursts with a strange "mushroom-like"
shape in the frequency–time domain, each one lasting several minutes. These
strange afternoon VLF emissions were recorded at Kannuslehto (KAN, ϕ
= 67.74° N, λ = 26.27° E; L ∼ 5.5) in northern Finland during the late recovery phase of the small
magnetic storm on 8 December 2013. The left-hand (LH) polarized 2–3 kHz
"mushroom caps" were clearly separated from the right-hand (RH) polarized
"mushroom stems" at the frequency of about 1.8–1.9 kHz, which could match the
lower ionosphere waveguide cutoff (the first transverse resonance of the
Earth–ionosphere cavity). We hypothesize that this VLF burst sequence could be a
result of the modulation of the VLF hiss electron–cyclotron instability from
the strong Pc5 geomagnetic pulsations observed simultaneously at
ground-based stations as well as in the inner magnetosphere by the Time History of Events and Macroscale Interactions during Substorms mission probe (THEMIS-E; ThE). This assumption is confirmed by a similar modulation of the
intensity of the energetic (1–10 keV) electrons simultaneously observed by
the same ThE spacecraft. In addition, the data of the European Incoherent Scatter Scientific Association (EISCAT) radar at
Tromsø show a similar quasi-periodicity in the ratio of the Hall-to-Pedersen conductance, which may be used as a proxy for the energetic
particle precipitation enhancement. Our findings suggest that this strange
mushroom-like shape of the considered VLF hiss could be a combined
mutual effect of the magnetospheric ULF–VLF (ultra low frequency–very low frequency) wave interaction and the
ionosphere waveguide propagation. |
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