Institution: | a Institute of Low Temperature Science, Hokkaido University, Kita-ku, Kita-19, Nishi-8, Sapporo 060-0819, Japan b Institute of Space and Astronautical Science, Sagamihara 229, Japan c Institute of Geophysics, University of Warsaw, ul. Pasteura 7, 02-093 Warsaw, Poland d Space Research Center, Polish Academy of Sciences, ul. Bartycka 18A, 00-716 Warsaw, Poland |