[1] SANSA Space Sci, Hermanus, South Africa
[2] Rhodes Univ, Dept Phys & Elect, Grahamstown, South Africa
[3] UCL, Dept Phys & Astron, London, England
[4] Univ Bergen, Dept Phys & Technol, Birkeland Ctr Space Sci, Bergen, Norway
[5] Univ Ctr Svalbard, Arctic Geophys, Longyearbyen, Norway
[6] Finnish Meteorol Inst, Helsinki, Finland
[7] Univ Lancaster, Dept Phys, Lancaster, England
[8] Univ Western Cape, Dept Phys & Astron, Bellville, South Africa