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Volume 36, issue 4 | Copyright
Ann. Geophys., 36, 1081-1097, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 08 Aug 2018

Regular paper | 08 Aug 2018

Cavitons and spontaneous hot flow anomalies in a hybrid-Vlasov global magnetospheric simulation

Xochitl Blanco-Cano1, Markus Battarbee2, Lucile Turc2, Andrew P. Dimmock3,8, Emilia K. J. Kilpua2, Sanni Hoilijoki4, Urs Ganse2, David G. Sibeck5, Paul A. Cassak6, Robert C. Fear7, Riku Jarvinen8,9, Liisa Juusola9,2, Yann Pfau-Kempf2, Rami Vainio10, and Minna Palmroth2,9 Xochitl Blanco-Cano et al.
  • 1Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
  • 2Department of Physics, University of Helsinki, Helsinki, Finland
  • 3Swedish Institute of Space Physics, Uppsala, Sweden
  • 4Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA
  • 5NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 6Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, USA
  • 7Department of Physics and Astronomy, University of Southampton, Southampton, UK
  • 8Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Espoo, Finland
  • 9Finnish Meteorological Institute, Helsinki, Finland
  • 10Department of Physics and Astronomy, University of Turku, Turku, Finland

Abstract. In this paper we present the first identification of foreshock cavitons and the formation of spontaneous hot flow anomalies (SHFAs) with the Vlasiator global magnetospheric hybrid-Vlasov simulation code. In agreement with previous studies we show that cavitons evolve into SHFAs. In the presented run, this occurs very near the bow shock. We report on SHFAs surviving the shock crossing into the downstream region and show that the interaction of SHFAs with the bow shock can lead to the formation of a magnetosheath cavity, previously identified in observations and simulations. We report on the first identification of long-term local weakening and erosion of the bow shock, associated with a region of increased foreshock SHFA and caviton formation, and repeated shock crossings by them. We show that SHFAs are linked to an increase in suprathermal particle pitch-angle spreads. The realistic length scales in our simulation allow us to present a statistical study of global caviton and SHFA size distributions, and their comparable size distributions support the theory that SHFAs are formed from cavitons. Virtual spacecraft observations are shown to be in good agreement with observational studies.

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Short summary
We use the Vlasiator code to study the characteristics of transient structures that exist in the Earth's foreshock, i.e. upstream of the bow shock. The structures are cavitons and spontaneous hot flow anomalies (SHFAs). These transients can interact with the bow shock. We study the changes the shock suffers via this interaction. We also investigate ion distributions associated with the cavitons and SHFAs. A very important result is that the arrival of multiple SHFAs results in shock erosion.
We use the Vlasiator code to study the characteristics of transient structures that exist in the...