Foreshock cavitons and spontaneous hot flow anomalies : a statistical study with a global hybrid-Vlasov simulation

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http://hdl.handle.net/10138/336008

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Tarvus , V , Turc , L , Battarbee , M , Suni , J , Blanco-Cano , X , Ganse , U , Pfau-Kempf , Y , Alho , M , Dubart , M , Grandin , M , Johlander , A , Papadakis , K & Palmroth , M 2021 , ' Foreshock cavitons and spontaneous hot flow anomalies : a statistical study with a global hybrid-Vlasov simulation ' , Annales Geophysicae , vol. 39 , no. 5 , pp. 911-928 . https://doi.org/10.5194/angeo-39-911-2021

Title: Foreshock cavitons and spontaneous hot flow anomalies : a statistical study with a global hybrid-Vlasov simulation
Author: Tarvus, Vertti; Turc, Lucile; Battarbee, Markus; Suni, Jonas; Blanco-Cano, Xochitl; Ganse, Urs; Pfau-Kempf, Yann; Alho, Markku; Dubart, Maxime; Grandin, Maxime; Johlander, Andreas; Papadakis, Konstantinos; Palmroth, Minna
Contributor organization: Particle Physics and Astrophysics
Space Physics Research Group
Department of Physics
Date: 2021-10-14
Language: eng
Number of pages: 18
Belongs to series: Annales Geophysicae
ISSN: 0992-7689
DOI: https://doi.org/10.5194/angeo-39-911-2021
URI: http://hdl.handle.net/10138/336008
Abstract: The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low-frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which are thought to evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward-southward angle of 45 degrees, continuous formation of cavitons is found up to similar to 11 Earth radii (R-E) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within similar to 2 R-E from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.
Subject: EARTHS FORESHOCK
MAGNETOSHEATH
CAVITIES
IMPACTS
WAVES
114 Physical sciences
1171 Geosciences
Peer reviewed: Yes
Rights: cc_by
Usage restriction: openAccess
Self-archived version: publishedVersion


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