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Volume 36, issue 3 | Copyright
Ann. Geophys., 36, 915-923, 2018
https://doi.org/10.5194/angeo-36-915-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

ANGEO Communicates 21 Jun 2018

ANGEO Communicates | 21 Jun 2018

New high-frequency (7–12 kHz) quasi-periodic VLF emissions observed on the ground at L  ∼  5.5

Jyrki Manninen1, Natalia Kleimenova2,3, Tauno Turunen1, and Liudmila Gromova4 Jyrki Manninen et al.
  • 1Sodankylä Geophysical Observatory, Sodankylä, Finland
  • 2Schmidt Institute of Physics of the Earth RAN, Moscow, Russia
  • 3Space Research Institute RAN, Moscow, Russia
  • 4Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAN, Moscow, Troitsk, Russia

Abstract. We reveal previously unknown quasi-periodic (QP) very low frequency (VLF) emissions at the unusually high-frequency band of  ∼ 7–12kHz by applying the digital filtering of strong atmospherics to the ground-based VLF data recorded at Kannuslehto station (KAN). It is located in northern Finland at L  ∼  5.5. The frequencies of QP emissions are much higher than the equatorial electron gyrofrequency at L  ∼  5.5. Thus, these emissions must have been generated at much lower L shells than KAN. Two high-frequency QP emission events have been studied in detail. The emissions were right-hand polarized waves indicating an overhead location of the exit area of waves in the ionosphere. In one event, the spectral–temporal forms of the emissions looked like a series of giant bullets due to the very abrupt cessation. Unfortunately, we could not explain such a strange dynamic spectral shape of the waves. In the second event, the modulation period was about 3min under the absence of simultaneous geomagnetic pulsations. The studied emissions lasted about 4h and were observed under the very quiet geomagnetic activity. The adequate mechanisms of the generation and propagation of the revealed high-frequency QP emissions have not yet been established. We speculate that studied QP emissions can be attributed to the auto-oscillations of the cyclotron instability in the magnetospheric plasma maser.

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We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusually high-frequency band of ~ 7–11 kHz by applying the digital filtering of strong sferics to the ground-based VLF data recorded at Kannuslehto station (KAN). In one event, the spectral–temporal forms of the emissions looked like a series of giant bullets, with very abrupt cessation. In the second event, the modulation period was about 3 min under the absence of the simultaneous geomagnetic pulsations.
We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusually high-frequency...
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