University of Oulu

Kilpua, E., Juusola, L., Grandin, M., Kero, A., Dubyagin, S., Partamies, N., Osmane, A., George, H., Kalliokoski, M., Raita, T., Asikainen, T., and Palmroth, M.: Cosmic noise absorption signature of particle precipitation during interplanetary coronal mass ejection sheaths and ejecta, Ann. Geophys., 38, 557–574,, 2020

Cosmic noise absorption signature of particle precipitation during interplanetary coronal mass ejection sheaths and ejecta

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Author: Kilpua, Emilia1; Juusola, Liisa2; Grandin, Maxime1;
Organizations: 1Department of Physics, University of Helsinki, Helsinki, Finland
2Finnish Meteorological Institute, Helsinki, Finland
3Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland
4Department of Arctic Geophysics, The University Centre in Svalbard, Longyearbyen, Norway
5Birkeland Centre for Space Science, Bergen, Norway
6ReSoLVE Center of Excellence, Space Climate Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 5.4 MB)
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Language: English
Published: Copernicus Publications, 2020
Publish Date: 2020-06-23


We study here energetic-electron (E>30 keV) precipitation using cosmic noise absorption (CNA) during the sheath and ejecta structures of 61 interplanetary coronal mass ejections (ICMEs) observed in the near-Earth solar wind between 1997 and 2012. The data come from the Finnish riometer (relative ionospheric opacity meter) chain from stations extending from auroral (IVA, 65.2 N geomagnetic latitude; MLAT) to subauroral (JYV, 59.0∘ N MLAT) latitudes. We find that sheaths and ejecta lead frequently to enhanced CNA (>0.5 dB) both at auroral and subauroral latitudes, although the CNA magnitudes stay relatively low (medians around 1 dB). Due to their longer duration, ejecta typically lead to more sustained enhanced CNA periods (on average 6–7 h), but the sheaths and ejecta were found to be equally effective in inducing enhanced CNA when relative-occurrence frequency and CNA magnitude were considered. Only at the lowest-MLAT station, JYV, ejecta were more effective in causing enhanced CNA. Some clear trends of magnetic local time (MLT) and differences between the ejecta and sheaths were found. The occurrence frequency and magnitude of CNA activity was lowest close to midnight, while it peaked for the sheaths in the morning and afternoon/evening sectors and for the ejecta in the morning and noon sectors. These differences may reflect differences in typical MLT distributions of wave modes that precipitate substorm-injected and trapped radiation belt electrons during the sheaths and ejecta. Our study also emphasizes the importance of substorms and magnetospheric ultra-low-frequency (ULF) waves for enhanced CNA.

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Series: Annales geophysicae
ISSN: 0992-7689
ISSN-E: 1432-0576
ISSN-L: 0992-7689
Volume: 38
Pages: 557 - 574
DOI: 10.5194/angeo-38-557-2020
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This research has been supported by the European Research Council (grant nos. 724391 SolMAG and 682068-PRESTISSIMO), the Norwegian Research Council (grant nos. 223252 and 287427), the Academy of Finland, Luonnontieteiden ja Tekniikan Tutkimuksen 5 Toimikunta (grant nos. 312351, 307411, 310445, 321440, 1312351, and 1309937), and the Tenure Track Project in Radio Science at the Sodankylä Geophysical Observatory of the University of Oulu.
Academy of Finland Grant Number: 312351
Detailed Information: 312351 (Academy of Finland Funding decision)
307411 (Academy of Finland Funding decision)
321440 (Academy of Finland Funding decision)
Copyright information: © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.