University of Oulu

Sivadas, N., Semeter, J., Nishimura, Y., & Kero, A. ( 2017). Simultaneous measurements of substorm‐related electron energization in the ionosphere and the plasma sheet. Journal of Geophysical Research: Space Physics, 122, 10,528– 10,547.

Simultaneous measurements of substorm‐related electron energization in the ionosphere and the plasma sheet

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Author: Sivadas, N.1; Semeter, J.1; Nishimura, Y.1,2;
Organizations: 1Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, Boston, MA, USA
2Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, CA, USA
3Sodankylä Geophysical Observatory and University of Oulu, Sodankylä, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.7 MB)
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Language: English
Published: American Geophysical Union, 2017
Publish Date: 2019-09-23


On 26 March 2008, simultaneous measurements of a large substorm were made using the Poker Flat Incoherent Scatter Radar, Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft, and all sky cameras. After the onset, electron precipitation reached energies ≳100 keV leading to intense D region ionization. Identifying the source of energetic precipitation has been a challenge because of lack of quantitative and magnetically conjugate measurements of loss cone electrons. In this study, we use the maximum entropy inversion technique to invert altitude profiles of ionization measured by the radar to estimate the loss cone energy spectra of primary electrons. By comparing them with magnetically conjugate measurements from THEMIS‐D spacecraft in the nightside plasma sheet, we constrain the source location and acceleration mechanism of precipitating electrons of different energy ranges. Our analysis suggests that the observed electrons ≳100 keV are a result of pitch angle scattering of electrons originating from or tailward of the inner plasma sheet at ~9RE, possibly through interaction with electromagnetic ion cyclotron waves. The electrons of energy 10–100 keV are produced by pitch angle scattering due to a potential drop of ≲10 kV in the auroral acceleration region (AAR) as well as wave–particle interactions in and tailward of the AAR. This work demonstrates the utility of magnetically conjugate ground‐ and space‐based measurements in constraining the source of energetic electron precipitation. Unlike in situ spacecraft measurements, ground‐based incoherent scatter radars combined with an appropriate inversion technique can be used to provide remote and continuous‐time estimates of loss cone electrons in the plasma sheet.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 122
Issue: 10
Pages: 10,528 - 10,547
DOI: 10.1002/2017JA023995
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported by the Air Force Office of Scientific Research under contract FA9550‐15‐1‐0503. The work of Y. Nishimura was supported by NASA grant NNX15AI62G and NNX15AI63G, NSF grant AGS‐1451911 and PLR‐1341359, and AFOSR grant FA9550‐15‐1‐0179. The work of A. Kero was supported by the European Regional Development Fund (Regional Council of Lapland, decision number A70179).
Copyright information: © 2017. American Geophysical Union. All Rights Reserved.