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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/angeo-2020-29
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-29
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 May 2020

25 May 2020

Review status
A revised version of this preprint was accepted for the journal ANGEO and is expected to appear here in due course.

Helium in the Earth’s foreshock: a global Vlasiator survey

Markus Battarbee1, Xochitl Blanco-Cano2, Lucile Turc1, Primož Kajdič2, Andreas Johlander1, Vertti Tarvus1, Stehphen Fuselier3,4, Karlheinz Trattner5, Markku Alho1, Thiago Brito1, Urs Ganse1, Yann Pfau-Kempf1, Mojtaba Akhavan-Tafti6,7, Tomas Karlsson8, Savvas Raptis8, Maxime Dubart1, Maxime Grandin1, Jonas Suni1, and Minna Palmroth1,9 Markus Battarbee et al.
  • 1Department of Physics, University of Helsinki, Finland
  • 2Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
  • 3Southwest Research Institute, San Antonio, Texas, USA
  • 4University of Texas San Antonio, San Antonio, USA
  • 5University of Colorado Boulder, Boulder, Colorado, USA
  • 6Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
  • 7LPP, CNRS, École Polytechnique, Sorbonne Université, Université Paris-Saclay, Observatoire de Paris, PSL Res Université, Institut Polytechnique de Paris, Palaiseau, France
  • 8School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
  • 9Finnish Meteorological Institute, Helsinki, Finland

Abstract. The foreshock is a region of space upstream of the Earth's bow shock extending along the interplanetary magnetic field. It is permeated by shock-reflected ions and electrons, low-frequency waves, and various plasma transients. We investigate the extent of the He2+ foreshock using Vlasiator, a global hybrid-Vlasov simulation. We perform the first numerical global survey of the helium foreshock, and interpret some historical foreshock observations in a global context.

The foreshock edge is populated by both proton and helium field-aligned beams, with the proton foreshock extending slightly further into the solar wind than the helium foreshock, and both extend well beyond the ULF wave foreshock. We compare our simulation results with MMS HPCA measurements, showing how the gradient of suprathermal ion densities at the foreshock crossing can vary between events. Our analysis suggests that the IMF cone angle and the associated shock obliquity gradient can play a role in explaining this differing behaviour.

We also investigate wave-ion-interactions with wavelet analysis and show that the dynamics and heating of He2+ must result from proton-driven ULF waves. Enhancements in ion agyrotropy are found in relation to, e.g., the ion foreshock boundary, the ULF foreshock boundary, and specular reflection of ions at the bow shock. We show that specular reflection can describe many of the foreshock ion VDF enhancements. Wave-wave-interactions deep in the foreshock cause decoherence of wavefronts, allowing He2+ the be scattered less than protons.

Markus Battarbee et al.

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Markus Battarbee et al.

Model code and software

Vlasiator: hybrid-Vlasov simulation code M. Palmroth and the Vlasiator team https://doi.org/10.5281/zenodo.3640593

Video supplement

Supplementary Video A M. Battarbee https://doi.org/10.5446/46641

Supplementary Video B M. Battarbee https://doi.org/10.5446/46638

Supplementary Video C Battarbee, Markus https://doi.org/10.5446/46639

Supplementary Video D M. Battarbee https://doi.org/10.5446/46640

Markus Battarbee et al.

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Latest update: 21 Sep 2020
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Short summary
We investigate the dynamics of helium in the foreshock, a part of near-Earth space found upstream of the Earth's bow shock. We show how the second-most common ion in interplanetary space reacts strongly to plasma waves found in the foreshock. Spacecraft observations and supercomputer simulations together give us new understanding of the foreshock edge and how to interpret future observations.
We investigate the dynamics of helium in the foreshock, a part of near-Earth space found...
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