1. Physical Sciences Division, British Antarctic Survey; Natural Environment Research Council; Cambridge; UK
2. Finnish Meteorological Institute; Helsinki; Finland
3. Physics Department; University of Otago; Dunedin; New Zealand
4. Sodankylä Geophysical Observatory; University of Oulu; Sodankylä; Finland
5. Space Research Group; Eötvös University; Budapest; Hungary
6. Research Group for Geoinformatics and Space Sciences; Geological Research Group of the Hungarian Academy of Sciences; Budapest; Hungary