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

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Battarbee , M , Blanco-Cano , X , Turc , L , Kajdic , P , Johlander , A , Tarvus , V , Fuselier , S , Trattner , K , Alho , M , Brito , T , Ganse , U , Pfau-Kempf , Y , Akhavan-Tafti , M , Karlsson , T , Raptis , S , Dubart , M , Grandin , M , Suni , J & Palmroth , M 2020 , ' Helium in the Earth's foreshock : a global Vlasiator survey ' , Annales Geophysicae , vol. 38 , no. 5 , pp. 1081-1099 . https://doi.org/10.5194/angeo-38-1081-2020

Title: Helium in the Earth's foreshock : a global Vlasiator survey
Author: Battarbee, Markus; Blanco-Cano, Xochitl; Turc, Lucile; Kajdic, Primoz; Johlander, Andreas; Tarvus, Vertti; Fuselier, Stephen; Trattner, Karlheinz; Alho, Markku; Brito, Thiago; Ganse, Urs; Pfau-Kempf, Yann; Akhavan-Tafti, Mojtaba; Karlsson, Tomas; Raptis, Savvas; Dubart, Maxime; Grandin, Maxime; Suni, Jonas; Palmroth, Minna
Other contributor: University of Helsinki, Space Physics Research Group
University of Helsinki, Space Physics Research Group
University of Helsinki, Space Physics Research Group
University of Helsinki, Space Physics Research Group
University of Helsinki, Space Physics Research Group
University of Helsinki, Department of Physics
University of Helsinki, Department of Physics
University of Helsinki, Particle Physics and Astrophysics
University of Helsinki, Space Physics Research Group
University of Helsinki, Particle Physics and Astrophysics
University of Helsinki, Space Physics Research Group
University of Helsinki, Department of Physics


Date: 2020-10-20
Language: eng
Number of pages: 19
Belongs to series: Annales Geophysicae
ISSN: 0992-7689
DOI: https://doi.org/10.5194/angeo-38-1081-2020
URI: http://hdl.handle.net/10138/321699
Abstract: The foreshock is a region of space upstream of the Earth's bow shock extending along the interplanetary magnetic field (IMF). 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 extending well beyond the ultra-low frequency (ULF) wave foreshock. We compare our simulation results with Magnetosphere Multiscale (MMS) Hot Plasma Composition Analyzer (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, for example, 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 velocity distribution function (VDF) enhancements. Wave-wave interactions deep in the foreshock cause de-coherence of wavefronts, allowing He2+ to be scattered less than protons.
Subject: FIELD-ALIGNED BEAMS
ALPHA-PARTICLES
ION DISTRIBUTIONS
BOW SHOCK
ULF FORESHOCK
UPSTREAM
PROTONS
WIND
ACCELERATION
PLASMA
115 Astronomy, Space science
114 Physical sciences
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