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Evidence for transient, local ion foreshocks caused by dayside magnetopause reconnection

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journal contribution
posted on 09.03.2017, 11:05 by Yann Pfau-Kempf, Heli Hietala, Steve E. Milan, Liisa Juusola, Sanni Hoilijoki, Urs Ganse, Sebastian von Alfthan, Minna Palmroth
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 ( 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.


The simulation was run on the Sisu supercomputer at the CSC – IT Center for Science, Espoo, Finland. We thank T. Mukai at ISAS, JAXA in Japan for providing Geotail/LEP data; S. Kokubun at STELAB, Nagoya University, Japan for providing Geotail/MGF data; A. Szabo at NASA/GSFC for providing Wind/MFI data; K. Ogilvie at NASA/GSFC for providing Wind/SWE data; R. Lin and S. Bale at UC Berkeley for providing Wind/3DP data; M. L. Kaiser at GSFC for providing Wind/WAVES data; N. Ness at Bartol Research Institute for providing ACE/MAG data; D. J. McComas at SWRI for providing ACE/SWEPAM data;and J. H. King and N. Papatashvili at AdnetSystems and GSFC for providing OMNI data, all through CDAweb. We also thank T. Nagai and Y. Saito for providing Geotail/MGF and Geotail/LEP data through DARTS at ISAS, JAXA in Japan. We thank the University of Kyoto for providing the AE electrojet indices through the World Data Center for Geomagnetism. We acknowledge the use of SuperDARN data. SuperDARN is a collection of radars funded by national scientific funding agencies of Australia, Canada, China, France, Japan, South Africa, United Kingdom and United States of America. We thank the institutes who maintain the IMAGE magnetometer array. Yann Pfau-Kempf, Sanni Hoilijoki, Sebastian von Alfthan and Minna Palmroth acknowledge financial support from the Academy of Finland under the project 267144/Vlasov. Part of this study was done by Yann Pfau-Kempf, Liisa Juusola, Urs Ganse, Sanni Hoilijoki and Minna Palmroth under the ERC CoG-682068- PRESTISSIMO project, a Consolidator grant to Minna Palmroth from the European Research Council. The work of Heli Hietala is funded by NASA contract NAS5-02099. Steve E. Milan was supported by the Science and Technology Facilities Council (STFC), UK, grant no. ST/N000749/1. Urs Ganse acknowledges funding from the German Research Foundation Grant GA1968/1 and the Academy of Finland project 267186. The topical editor, C. Owen, thanks



Annales Geophysicae, 2016, 34 (11), pp. 943-959 (17)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Annales Geophysicae


European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)





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The simulation dataset is available on request from the Vlasiator team (, von Alfthan et al., 2014). IMAGE magnetometer data are available from http: // (Tanskanen, 2009). The AACGM software is available from superdarn/aacgm.html (Shepherd, 2014). The SuperDARN data can be accessed from the SuperDARN data portal hosted by Virginia Tech at (Greenwald et al., 1995). The Supplement related to this article is available online at doi:10.5194/angeo-34-943-2016-supplement.