1. Department of Physics and Astronomy; University of Southampton; Southampton UK
2. Jodrell Bank Centre for Astrophysics; University of Manchester; Manchester UK
3. Sodankylä Geophysical Observatory; University of Oulu, Tähteläntie 62; Sodankylä Finland
4. STFC Rutherford Appleton Laboratory; Harwell Science and Innovation Campus; Didcot UK