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Localization of the source of quasiperiodic VLF emissions in the magnetosphere by using simultaneous ground and space observations: a case study
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  • Andrei G. Demekhov,
  • Elena E Titova,
  • Jyrki Maninnen,
  • Andris A. Lubchich,
  • Alexey V. Larchenko,
  • Dmitry Pasmanik,
  • Ondrej Santolík,
  • Tauno Turunen,
  • Alexander Nikitenko
Andrei G. Demekhov
Institute of Applied Physics, Russian Academy of Sciences

Corresponding Author:[email protected]

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Elena E Titova
Polar Geophysical Institute
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Jyrki Maninnen
Sodankyla Geophysical Observatory
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Andris A. Lubchich
Polar Geophysical Institute
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Alexey V. Larchenko
Polar Geophysical Institute
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Dmitry Pasmanik
Institute of Applied Physics Russian Academy of Science
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Ondrej Santolík
Department of Space Physics, Institute of Atmospheric Physics, The Czech Academy of Sciences, Prague, Czech Republic
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Tauno Turunen
Sodankylä Geophysical Observatory
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Alexander Nikitenko
Polar Geophysical Institute
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Abstract

We study quasi-periodic VLF emissions observed simultaneously by Van Allen Probes spacecraft and Kannuslehto and Lovozero ground-based stations on 25 December 2015. Both Van Allen Probes A and B detected quasi-periodic emissions, probably originated from a common source, and observed on the ground. In order to locate possible regions of wave generation, we analyze wave normal angles with respect to the geomagnetic field, Poynting flux direction, and cyclotron instability growth rate calculated by using the measured phase space density of energetic electrons. We demonstrate that even parallel wave propagation and proper (downward) Poynting flux direction are not sufficient for claiming observations to be in the source region. Agreement between the growth rate and emission bands was obtained for a restricted part of Van Allen Probe A trajectory corresponding to localized enhancement of plasma density with scale of 700~km. We employ spacecraft density data to build a model plasma profile and to calculate ray trajectories from the point of wave detection in space to the ionosphere, and examine the possibility of their exit to the ground. For the considered event, the wave could exit to the ground in the geomagnetic flux tube with enhanced plasma density, that ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point.
May 2020Published in Journal of Geophysical Research: Space Physics volume 125 issue 5. 10.1029/2020JA027776