University of Oulu

Manninen, J., Kleimenova, N., Turunen, T., Nikitenko, A., Gromova, L., & Fedorenko, Y. (2021). New type of short high-frequency VLF patches (“VLF birds”) above 4–5 kHz. Journal of Geophysical Research: Space Physics, 126, e2020JA028601. https://doi.org/10.1029/2020JA028601

New type of short high-frequency VLF patches (“VLF birds”) above 4–5 kHz

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Author: Manninen, Jyrki1; Kleimenova, Natalia2,3; Turunen, Tauno1;
Organizations: 1Sodankylä Geophysical Observatory, Sodankylä, Finland
2Electromagnetic fields, Schmidt Institute of Physics of the Earth RAN, Moscow, Russia
3Space Plasma, Space Research Institute RAS, Moscow, Russia
4Apatity Division, Polar Geophysical Institute, Apatity, Russia
5Ionosphere and Radio Wave Propagation (IZMIRAN), Pushkov Institute of Terrestrial Magnetism, Moscow, Russia
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 7.8 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2021070140715
Language: English
Published: American Geophysical Union, 2021
Publish Date: 2021-07-01
Description:

Abstract

The new type of daytime natural very low frequency (VLF) whistler mode emissions of the magnetospheric origin was found in the VLF observations at Kannuslehto station (L ∼ 5.5) in Northern Finland. The events occurred at the frequencies above 4–5 kHz even up to 15 kHz. These emissions have never been observed earlier in the spectrograms because they were hidden by strong impulsive atmospherics (sferics) in the same frequency range originating in lightning discharges. After filtering out the sferics, we surprisingly discovered completely new types of high frequency right-hand polarized peculiar VLF emissions with various unusual dynamic spectra. These new VLF emissions typically occur as a sequence of a number of short (∼1–3 min) burst-like structures or single short patches with the total duration up to a few hours. The spectral peculiarities of several long-lasting VLF events as well as individual short VLF patches are discussed. The dynamic spectra of these new VLF patches raise the question of the temporal and spatial details of the wave-particle interactions in the magnetospheric plasma. These emissions are observed only under quiet or weakly disturbed space weather conditions, but during small negative values of the Dst index, indicating the presence of a certain excess of the radiation belt electrons. Note, these high frequency VLF patches are observed at the frequencies much higher than the half of the equatorial electron gyrofrequency which is equal to ∼2.7 kHz at L ∼ 5.5. It seems that these emissions are generated deep in the magnetosphere, but the detailed nature, generation region, and propagation behavior of these newly discovered VLF emissions remain unknown. An appearance of high frequency VLF patches could be an indirect indicator of a local enhancement of electron fluxes in the radiation belt that are not directly measured and may occur even in the absence of visible ground-based geomagnetic disturbances. Further researches may shed new light on wave-particle interactions occurring in the Earth's radiation belts.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 126
Issue: 4
Article number: e2020JA028601
DOI: 10.1029/2020JA028601
OADOI: https://oadoi.org/10.1029/2020JA028601
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
115 Astronomy and space science
Subjects:
Funding: The work of N. Kleimenova, L. Gromova, Y. Fedorenko, and A. Nikitenko was supported by the grants of Academy of Finland (no. 308501 for N. Kleimenova, L. Gromova and Y. Fedorenko, and no. 315716 for A. Nikitenko).
Academy of Finland Grant Number: 308501
315716
Detailed Information: 308501 (Academy of Finland Funding decision)
315716 (Academy of Finland Funding decision)
Copyright information: © 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
  https://creativecommons.org/licenses/by-nc/4.0/