Evidence for transient, local ion foreshocks caused by dayside magnetopause reconnection Yann Pfau-Kempf Heli Hietala Steve E. Milan Liisa Juusola Sanni Hoilijoki Urs Ganse Sebastian von Alfthan Minna Palmroth 2381/39425 https://figshare.le.ac.uk/articles/journal_contribution/Evidence_for_transient_local_ion_foreshocks_caused_by_dayside_magnetopause_reconnection/10229192 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. 2017-03-09 11:05:27 Science & Technology Physical Sciences Astronomy & Astrophysics Geosciences, Multidisciplinary Meteorology & Atmospheric Sciences Geology Interplanetary physics (planetary bow shocks) magnetospheric physics (magnetosheath; solar wind-magnetosphere interactions) FLUX-TRANSFER EVENTS EARTHS BOW SHOCK INTERPLANETARY MAGNETIC-FIELD HIGH-LATITUDE MAGNETOPAUSE ELEMENTARY CURRENT SYSTEMS HYBRID-VLASOV SIMULATION WIND SPACECRAFT THEMIS OBSERVATIONS CLUSTER SPACECRAFT RADAR OBSERVATIONS