University of Oulu

Yahnin, A. G., Popova, T. A., Demekhov, A. G., Lubchich, A. A., Matsuoka, A., Asamura, K., et al. (2021). Evening side EMIC waves and related proton precipitation induced by a substorm. Journal of Geophysical Research: Space Physics, 126, e2020JA029091.

Evening side EMIC waves and related proton precipitation induced by a substorm

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Author: Yahnin, A. G.1; Popova, T. A.1; Demekhov, A. G.1,2;
Organizations: 1Polar Geophysical Institute, Apatity, Russia
2Institute of Applied Physics of the RAS, Nizhny Novgorod, Russia
3JAXA, Sagamihara, Japan
4Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan
5Osaka University, Osaka, Japan
6The University of Tokyo, Tokyo, Japan
7Tohoku University, Sendai, Japan
8Kanazawa University, Kanazawa, Japan
9New Jersey Institute of Technology, Newark, NJ, USA
10Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.2 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2021-12-17


We present the results of a multi-point and multi-instrument study of electromagnetic ion cyclotron (EMIC) waves and related energetic proton precipitation during a substorm. We analyze the data from Arase (ERG) and Van Allen Probes (VAPs) A and B spacecraft for an event of 16 and 17 UT on December 1, 2018. VAP-A detected an almost dispersionless injection of energetic protons related to the substorm onset in the night sector. Then the proton injection was detected by VAP-B and further by Arase, as a dispersive enhancement of energetic proton flux. The proton flux enhancement at every spacecraft coincided with the EMIC wave enhancement or appearance. This data show the excitation of EMIC waves first inside an expanding substorm wedge and then by a drifting cloud of injected protons. Low-orbiting NOAA/POES and MetOp satellites observed precipitation of energetic protons nearly conjugate with the EMIC wave observations in the magnetosphere. The proton pitch-angle diffusion coefficient and the strong diffusion regime index were calculated based on the observed wave, plasma, and magnetic field parameters. The diffusion coefficient reaches a maximum at energies corresponding well to the energy range of the observed proton precipitation. The diffusion coefficient values indicated the strong diffusion regime, in agreement with the equality of the trapped and precipitating proton flux at the low-Earth orbit. The growth rate calculations based on the plasma and magnetic field data from both VAP and Arase spacecraft indicated that the detected EMIC waves could be generated in the region of their observation or in its close vicinity.

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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: 7
Article number: e2020JA029091
DOI: 10.1029/2020JA029091
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The analysis of pulsation magnetometer data was supported by the Academy of Finland (Grant #330783 to Sodankylä Geophysical Observatory). The work of A. G. Yahnin, T. A. Popova, and A. G. Demekhov was supported by the Russian Foundation for Basic Research (Grant no. 19-52-50025). The work has also been supported by JSPS KAKENHI (JPJSBP120194814, 15H05747, 16H06286, 17H00728, 20H01959, and 20H01955). The work at the New Jersey Institute of Technology (NJIT) was supported by NSF under Grant AGS-1602560 and the NASA Van Allen Probes RBSPICE instrument project, as supported by JHU/APL Subcontract no. 131803 to NJIT under NASA Prime Contract no. NNN06AA01C.
Academy of Finland Grant Number: 330783
Detailed Information: 330783 (Academy of Finland Funding decision)
Dataset Reference: Van Allen Probe data used in this study can be found in the EMFISIS (, and RBSP-ECT ( archives. Science data of the Arase (ERG) satellite were obtained from the ERG Science Center operated by ISAS/JAXA and ISEE/Nagoya University (, Miyoshi, Hori, et al., 2018). The present study analyzed MGF-L2 v03_04 data (Matsuoka, Teramoto, Imajo, et al., 2018), EFD/PWE-L2 v01 (Kasahara et al., 2020), LEP-i-L2 3D flux v03_00 data (Asamura, Miyoshi, et al., 2018), MEP-i-L2 3D flux v01_02 data (Yokota et al., 2019), and Orbit L3 v01 data (Miyoshi, Shinohara, & Jun, 2018).
Copyright information: © 2021. American Geophysical Union.