1. The Blackett Laboratory, Department of Physics , Imperial College London , London SW7 2AZ, UK
2. Istituto per la Scienza e Tecnologia dei Plasmi (ISTP), Consiglio Nazionale delle Ricerche , Via Amendola 122/D, I-70126 Bari, Italy
3. Department of Physics and Astronomy, Queen Mary University of London , London, E1 4NS, UK
4. Space Research Institute, Austrian Academy of Sciences , Graz, A-8042, Austria
5. Departamento de Ciencias Espaciales, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria , Ciudad de México, 0451, Mexico
6. Department of Physics and Astronomy, University of Turku , FI-20014 Turku, Finland
7. LPP, Ecole Polytechnique, CNRS, UPMC, Université Paris Sud , Palaiseau, F-91128, France
8. INAF – Istituto di Astrofisica e Planetologia Spaziali , Rome, I-00133, Italy
9. Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology , Stockholm, SE-100 44, Sweden
10. Swedish Institute of Space Physics (IRF), Ångström Laboratory , Lägerhyddsvägen 1, SE-75121 Uppsala, Sweden
11. Dipartimento di Fisica, Università della Calabria , I-87036 Rende, Italy