Ground and space signatures of VLF noise suppression by whistlers

0522721 - ÚFA 2021 RIV US eng J - Journal Article
Shklyar, D. R. - Manninen, J. - Titova, E. E. - Santolík, Ondřej - Kolmašová, Ivana - Turunen, T.
Ground and space signatures of VLF noise suppression by whistlers.
Journal of Geophysical Research-Space Physics. Roč. 125, č. 2 (2020), č. článku e2019JA027430. ISSN 2169-9380. E-ISSN 2169-9402
R&D Projects: GA ČR(CZ) GA17-07027S
Grant - others:AV ČR(CZ) AP1401
Program: Akademická prémie - Praemium Academiae
Institutional support: RVO:68378289
Keywords : mode waves * emissions * hiss
OECD category: Fluids and plasma physics (including surface physics)
Impact factor: 2.811, year: 2020
Method of publishing: Open access
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JA027430

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 similar to 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.
Permanent Link: http://hdl.handle.net/11104/0307168