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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-150
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-150
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: regular paper 06 Nov 2019

Submitted as: regular paper | 06 Nov 2019

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

Outer radiation belt and inner magnetospheric response to sheath regions of coronal mass ejections: A statistical analysis

Milla M. H. Kalliokoski1, Emilia K. J. Kilpua1, Adnane Osmane1, Drew L. Turner2, Allison N. Jaynes3, Lucile Turc1, Harriet George1, and Minna Palmroth1,4 Milla M. H. Kalliokoski et al.
  • 1Department of Physics, University of Helsinki, Helsinki, Finland
  • 2Space Sciences Department, The Aerospace Corporation, El Segundo, California, USA
  • 3Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA
  • 4Finnish Meteorological Institute, Helsinki, Finland

Abstract. The energetic electron content in the Van Allen radiation belts surrounding the Earth can vary dramatically on several timescales, and these strong electron fluxes present a hazard for spacecraft traversing the belts. The belt response to solar wind driving is yet largely unpredictable and especially the direct response to specific large-scale heliospheric structures has not been considered previously. We investigate the immediate response of electron fluxes in the outer belt to driving by sheath regions preceding interplanetary coronal mass ejections and the associated wave activity in the inner magnetosphere. We consider events from 2012 to 2018 in the Van Allen Probes era to employ the energy and radial distance resolved electron flux observations of the twin spacecraft mission. We perform a statistical study of the events using superposed epoch analysis, where the sheaths are superposed separately from the ejecta and resampled to the same average duration. Our results show that wave power of ultra-low frequency Pc5 and electromagnetic ion cyclotron waves, as measured by a geostationary GOES satellite, is higher during the sheaths than during the ejecta. However, the level of chorus wave power remains approximately the same, despite on average stronger ring current enhancements during the ejecta. Electron flux enhancements are common at low energies (< 1 MeV) throughout the outer belt (L = 3–6), whereas depletion occurs predominantly at high energies for high L-shells (L > 4). Distinctively, depletion extends to lower energies at larger distances. We suggest that this L-shell and energy dependent depletion results from magnetopause shadowing dominating the losses at large distances, while wave-particle interactions dominate closer to the Earth. We also show that non-geoeffective sheaths cause significant changes in the outer belt electron fluxes.

Milla M. H. Kalliokoski et al.
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Milla M. H. Kalliokoski et al.
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Short summary
We present a comprehensive statistical study of the response of the Earth’s space environment during sheath regions preceding interplanetary coronal mass ejections. Inner magnetospheric wave activity is enhanced during sheath regions, and sheaths cause significant changes in the outer radiation belt electron fluxes on short time scales. We show that also non-geoeffective sheaths can result in a significant response.
We present a comprehensive statistical study of the response of the Earth’s space environment...
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