Evidence for transient, local ion foreshocks caused by dayside magnetopause reconnection
- 1Earth Observation, Finnish Meteorological Institute, Helsinki, Finland
- 2Department of Physics, University of Helsinki, Helsinki, Finland
- 3Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, USA
- 4Department of Physics and Astronomy, University of Leicester, Leicester, UK
- 5Department of Physics and Astronomy, University of Turku, Turku, Finland
- 6CSC, IT Center for Science, Espoo, Finland
Abstract. We present a scenario resulting in time-dependent behaviour of the bow shock and transient, local ion reflection under unchanging solar wind conditions. Dayside magnetopause reconnection produces flux transfer events driving fast-mode wave fronts in the magnetosheath. These fronts push out the bow shock surface due to their increased downstream pressure. The resulting bow shock deformations lead to a configuration favourable to localized ion reflection and thus the formation of transient, travelling foreshock-like field-aligned ion beams. This is identified in two-dimensional global magnetospheric hybrid-Vlasov simulations of the Earth's magnetosphere performed using the Vlasiator model (http://vlasiator.fmi.fi). We also present observational data showing the occurrence of dayside reconnection and flux transfer events at the same time as Geotail observations of transient foreshock-like field-aligned ion beams. The spacecraft is located well upstream of the foreshock edge and the bow shock, during a steady southward interplanetary magnetic field and in the absence of any solar wind or interplanetary magnetic field perturbations. This indicates the formation of such localized ion foreshocks.