University of Oulu

Shklyar, D. R., Manninen, J., Titova, E. E., Santolík, O., Kolmašová, I., & Turunen, T. ( 2020). Ground and space signatures of VLF noise suppression by whistlers. Journal of Geophysical Research: Space Physics, 125, e2019JA027430. https://doi.org/10.1029/2019JA027430

Ground and space signatures of VLF noise suppression by whistlers

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Author: Shklyar, D. R.1,2; Manninen, J.3; Titova, E. E.1,4;
Organizations: 1Space Research Institute, Russian Academy of Sciences, Moscow, Russia
2Department of Physics, National Research University Higher School of Economics, Moscow, Russia
3Sodankylä Geophysical Observatory, Sodankylä, Finland
4Polar Geophysical Institute, Apatity, Russia
5Department of Space Physics, Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, Czechia
6Faculty of Mathematics and Physics, Charles University, Prague, Czechia
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 28.7 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2020050424945
Language: English
Published: American Geophysical Union, 2020
Publish Date: 2020-05-04
Description:

Abstract

VLF (VeryLow Frequency) spectrograms registered at Kannuslehto ground station, after cleaning them from strong sferics, reveal VLF noise suppression by whistlers and whistler echo trains, which consists in significant reduction in the noise spectral power after a strong whistler event. We have found similar effect in the VLF data from Van Allen Probe B taken in the equatorial region on L‐shell ~3. Detailed analysis of the data shows that the whistler echo train and the VLF noise have small wave normal angles. Based on this observation, we limit our analysis to parallel (ducted) whistler wave propagation. The persistence of whistler echo train, as well as the VLF noise, suggests that in the events under discussion, plasma is unstable in the frequency range corresponding to the observed VLF noise band. In an attempt to explain the effect of VLF noise suppression, we follow up the long‐standing idea that relates this effect to the reduction of free energy in the unstable plasma distribution by whistler echo train. To develop this idea into qualitative model, we have studied the motion of energetic electrons, responsible for the noise generation, in the field of ducted whistler echo train. We show that energetic electrons that make the main contribution to the growth rate of VLF noise, during their bounce oscillations in the magnetosphere, are subject to multiple resonant impacts from the whistler echo train. These lead to energetic electron diffusion in the phase space and the corresponding reduction in free energy of the unstable distribution.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 125
Issue: 2
Pages: 1 - 14
Article number: e2019JA027430
DOI: 10.1029/2019JA027430
OADOI: https://oadoi.org/10.1029/2019JA027430
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Subjects:
Funding: This study was done in the frame of the Grant 294931 of the Academy of Sciences of Finland. D. R. S. and E. E. T. also acknowledge support from RFBR Grant 19‐02‐00179. O. S. and I. K. acknowledge support from Grants LTAUSA17070, GACR 17‐07027S, and the Praemium Academiae award from the CAS. The authors thank the PI of EMFISIS instrument C. Kletzing and the PI of MagEIS instrument H. Spence of Van Allen Probes team for the use of the data which is available online (http://cdaweb.sci.gsfc.nasa.gov/istp_public/). SGO ELF‐VLF quicklook plots are available online (http://www.sgo.fi/pub_vlf/).
Academy of Finland Grant Number: 294931
Detailed Information: 294931 (Academy of Finland Funding decision)
Copyright information: © 2020. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.
  https://creativecommons.org/licenses/by-nc-nd/4.0/