24 Feb 2021

24 Feb 2021

Review status: this preprint is currently under review for the journal ANGEO.

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

Vertti Tarvus1, Lucile Turc1, Markus Battarbee1, Jonas Suni1, Xóchitl Blanco-Cano2, Urs Ganse1, Yann Pfau-Kempf1, Markku Alho1, Maxime Dubart1, Maxime Grandin1, Andreas Johlander1, Konstantinos Papadakis1, and Minna Palmroth1,3 Vertti Tarvus et al.
  • 1Department of Physics, University of Helsinki, Helsinki, Finland
  • 2Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico City, Mexico
  • 3Finnish Meteorological Institute, Helsinki, Finland

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 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 ~ 11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ~ 2 RE 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 the 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.

Vertti Tarvus et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2020-87', Anonymous Referee #1, 26 Mar 2021
  • RC2: 'Comment on angeo-2020-87', Anonymous Referee #2, 23 Apr 2021

Vertti Tarvus et al.

Model code and software

Vlasiator: hybrid-Vlasov simulation code Minna Palmroth and the Vlasiator team

Analysator: python analysis toolkit Markus Battarbee and the Vlasiator team

Vertti Tarvus et al.


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