1. National Institute of Polar Research Tachikawa Japan
2. Ionospheric Physics Research UnitUniversity of Oulu Oulu Finland
3. Department of Communication Engineering and InformaticsUniversity of Electro‐Communications Chofu Japan
4. Department of Polar ScienceSOKENDAI (The Graduate University for Advanced Studies) Tachikawa Japan
5. Sodankylä Geophysical ObservatoryUniversity of Oulu Sodankylä Finland