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Volume 33, issue 8
Ann. Geophys., 33, 991–995, 2015
https://doi.org/10.5194/angeo-33-991-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 33, 991–995, 2015
https://doi.org/10.5194/angeo-33-991-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

ANGEO Communicates 12 Aug 2015

ANGEO Communicates | 12 Aug 2015

Strange VLF bursts in northern Scandinavia: case study of the afternoon "mushroom-like" hiss on 8 December 2013

J. Manninen1, N. G. Kleimenova2,3, A. Kozlovsky1, I. A. Kornilov4, L. I. Gromova5, Y. V. Fedorenko4, and T. Turunen1 J. Manninen et al.
  • 1Sodankylä Geophysical Observatory, 99600 Sodankylä, Finland
  • 2Schmidt Institute of Physics of the Earth, RAS, Moscow, 123955, Russia
  • 3Space Research Institute, RAS, Moscow, 117997, Russia
  • 4Polar Geophysical Institute, RAS, Apatity, 184209, Russia
  • 5Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, RAS, Troitsk, 142190, Russia

Abstract. 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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A non-typical 1-4 kHz hiss was studied. It shows a sequence of separated noise bursts with strange “mushroom-like” shapes in the frequency-time domain, each lasting several minutes. This sequence could be a result of the modulation of the VLF hiss electron-cyclotron instability by Pc5 geomagnetic pulsations. This strange “mushroom-like” shape of the considered VLF hiss could be a combined mutual effect of the magnetospheric ULF-VLF wave interaction and the ionosphere waveguide propagation.
A non-typical 1-4 kHz hiss was studied. It shows a sequence of separated noise bursts with...
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