1. Space and Atmospheric Physics Group, The Blackett Laboratory; Imperial College London; London UK
2. Atmospheric Physics Laboratory, Department of Physics and Astronomy; University College London; London UK
3. Heliophysics Science Division; NASA GSFC; Greenbelt Maryland USA
4. Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
5. Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
6. Centre for Planetary Sciences; University College London; London UK