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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: regular paper 03 Dec 2019

Submitted as: regular paper | 03 Dec 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Cosmic noise absorption signature of particle precipitation during ICME sheaths and ejecta

Emilia Kilpua1, Liisa Juusola2, Maxime Grandin1, Antti Kero3, Stepan Dubyagin2, Noora Partamies4,5, Adnane Osmane1, Harriet George1, Milla Kalliokoski1, Tero Raita3, Timo Asikainen6, and Minna Palmroth1,2 Emilia Kilpua et al.
  • 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 Centre of Excellence, Space Climate Research Unit, University of Oulu, Oulu, Finland

Abstract. We study here energetic (E > 30 keV) electron 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 comes from the Finnish riometer chain from stations extending from auroral (IVA, 65.2 geomagnetic latitude, MLAT) to subauroral (JYV, 59.0 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 hours), 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 magnetic local time (MLT) trends and differences between the ejecta and sheath 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 sheath and ejecta. Our study also emphasizes the importance of substorms and magnetospheric ULF waves for enhanced CNA.

Emilia Kilpua et al.
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Status: open (until 28 Jan 2020)
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Emilia Kilpua et al.
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Short summary
Coronal mass ejection sheaths and ejecta are key drivers of significant space weather storms and they cause dramatic changes in radiation belt electron fluxes. Differences in precipitation of high-energy electrons from the belts to the upper atmosphere is thus expected. We investigate here differences in sheath and ejecta induced precipitation using the Finnish riometer chain.
Coronal mass ejection sheaths and ejecta are key drivers of significant space weather storms and...