Foreshock Properties at Typical and Enhanced Interplanetary Magnetic Field Strengths: Results From Hybrid-Vlasov Simulations

Research output: Contribution to journalArticleScientificpeer-review

Researchers

  • L. Turc
  • U. Ganse
  • Y. Pfau-Kempf
  • S. Hoilijoki
  • M. Battarbee
  • L. Juusola
  • Riku Järvinen

  • T. Brito
  • M. Grandin
  • M. Palmroth

Research units

  • University of Helsinki
  • University of Colorado Boulder
  • Finnish Meteorological Institute

Abstract

In this paper, we present a detailed study of the effects of the interplanetary magnetic field (IMF) strength on the foreshock properties at small and large scales. Two simulation runs performed with the hybrid-Vlasov code Vlasiator with identical setup but with different IMF strengths, namely, 5 and 10 nT, are compared. We find that the bow shock position and shape are roughly identical in both runs, due to the quasi-radial IMF orientation, in agreement with previous magnetohydrodynamic simulations and theory. Foreshock waves develop in a broader region in the higher IMF strength run, which we attribute to the larger growth rate of the waves. The velocity of field-aligned beams remains essentially the same, but their density is generally lower when the IMF strength increases, due to the lower Mach number. Also, we identify in the regular IMF strength run ridges of suprathermal ions which disappear at higher IMF strength. These structures may be a new signature of the foreshock compressional boundary. The foreshock wave field is structured over smaller scales in higher IMF conditions, due to both the period of the foreshock waves and the transverse extent of the wave fronts being smaller. While the foreshock is mostly permeated by monochromatic waves at typical IMF strength, we find that magnetosonic waves at different frequencies coexist in the other run. They are generated by multiple beams of suprathermal ions, while only a single beam is observed at typical IMF strength. The consequences of these differences for solar wind-magnetosphere coupling are discussed.

Details

Original languageEnglish
Pages (from-to)5476-5493
JournalJournal of geophysical research: Space physics
Volume123
Issue number7
Publication statusPublished - Jul 2018
MoE publication typeA1 Journal article-refereed

    Research areas

  • Bow shock, Foreshock, Kinetic simulations, Numerical simulations, Plasma waves, ULF waves

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