1. School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK
2. Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Dorking, RH5 6NT, UK
3. School of Cosmic Physics, DIAS Dunsink Observatory, Dublin Institute for Advanced Studies, Dublin 15, Dublin, Ireland
4. Harvard–Smithsonian Center for Astrophysics, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, USA
5. Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
6. Center for Space Physics, Boston University, Boston, MA 02215, USA
7. Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX 78238,, USA
8. Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA