Localization of the Source of Quasiperiodic VLF Emissions in the Magnetosphere by Using Simultaneous Ground and Space Observations: A Case Study

We study quasiperiodic very low frequency (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 quasiperiodic emissions, probably originated from a common source, and obser...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2020-05, Vol.125 (5), p.n/a
Main Authors: Demekhov, A. G., Titova, E. E., Maninnen, J., Pasmanik, D. L., Lubchich, A. A., Santolík, O., Larchenko, A. V., Nikitenko, A. S., Turunen, T.
Format: Article
Language:English
Subjects:
cyclotron instability
Cyclotrons
Fluctuations
Flux
Geomagnetic field
Geomagnetism
Ground stations
Ground-based observation
Growth rate
Ionosphere
Ionospheric propagation
Localization
magnetosphere
Magnetospheres
Plasma density
Probes
Propagation
quasiperiodic VLF emissions
Space density
Spacecraft
Very Low Frequencies
VLF emissions
Wave generation
Wave propagation
whistler mode waves
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Summary:We study quasiperiodic very low frequency (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 quasiperiodic 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 propagation toward the ground. For the considered event, the wave could propagate toward the ground in the geomagnetic flux tube with enhanced plasma density, which ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point. Key Points Complex analysis of generation region of quasiperiodic VLF emissions were observed simultaneously by two Van Allen Probes and on the ground Wave growth rate frequency band matched the observed emission band only in a localized (∼0.3 Earth radii) region along Van Allen Probe A trajectory Ray tracing demonstrated the importance of a density duct for wave propagation toward the ground
ISSN:2169-9380
2169-9402
DOI:10.1029/2020JA027776