University of Oulu

Tesfaw, H. W., Virtanen, I. I., Aikio, A. T., Nel, A., Kosch, M., & Ogawa, Y. (2022). Precipitating electron energy spectra and auroral power estimation by incoherent scatter radar with high temporal resolution. Journal of Geophysical Research: Space Physics, 127(4).

Precipitating electron energy spectra and auroral power estimation by incoherent scatter radar with high temporal resolution

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Author: Tesfaw, Habtamu W.1; Virtanen, Ilkka I.1; Aikio, Anita T.1;
Organizations: 1Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
2South African National Space Agency, Hermanus, South Africa
3Department of Physics, Lancaster University, Lancaster, UK
4Department of Physics and Astrophysics, University of Western Cape, Bellville, South Africa
5National Institute of Polar Research, Tokyo, Japan
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.6 MB)
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Language: English
Published: American Geophysical Union, 2022
Publish Date: 2022-12-19


This study presents an improved method to estimate differential energy flux, auroral power and field-aligned current of electron precipitation from incoherent scatter radar data. The method is based on a newly developed data analysis technique that uses Bayesian filtering to fit altitude profiles of electron density, electron temperature, and ion temperature to observed incoherent scatter spectra with high time and range resolutions. The electron energy spectra are inverted from the electron density profiles. Previous high-time resolution fits have relied on the raw electron density, which is calculated from the backscattered power assuming that the ion and electron temperatures are equal. The improved technique is applied to one auroral event measured by the EISCAT UHF radar and it is demonstrated that the effect of electron heating on electron energy spectra, auroral power, and upward field-aligned current can be significant at times. Using the fitted electron densities instead of the raw ones may lead to wider electron energy spectra and auroral power up to 75% larger. The largest differences take place for precipitation that produces enhanced electron heating in the upper E region, and in this study correspond to fluxes of electrons with peak energies from 3 to 5 keV. Finally, the auroral power estimates are verified by comparison to the 427.8 nm auroral emission intensity, which shows good correlation. The improved method makes it possible to calculate unbiased estimates of electron energy spectra with high time resolution and thereby to study rapidly varying aurora.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 127
Issue: 4
Article number: e2021JA029880
DOI: 10.1029/2021ja029880
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work is supported by the Academy of Finland (301542) and the Kvantum Institute of the University of Oulu.
Dataset Reference: EISCAT data are available for download from The auroral blue line emission intensity data used in this study is available at, and quick- look images for the Watec monochromatic imager (WMI) can be acessed from The image magnetometer network data is available at defined.
Copyright information: © 2022 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.