[1] OSAKA UNIV,FAC SCI,DEPT EARTH & SPACE SCI,TOYONAKA,OSAKA 560,JAPAN
[2] TOHOKU UNIV,FAC SCI,DEPT GEOPHYS & ASTRON,SENDAI,MIYAGI 990,JAPAN
[3] NAGOYA UNIV,FAC SCI,DEPT PHYS,CHIKUSA KU,NAGOYA,AICHI 46401,JAPAN
[4] INST SPACE & ASTRONAUT SCI,SAGAMIHARA,KANAGAWA 229,JAPAN
[5] UNIV TOKYO,FAC SCI,DEPT EARTH & PLANETARY PHYS,BUNKYO KU,TOKYO 113,JAPAN
[6] TOHOKU UNIV,UPPER ATMOSPHERE & SPACE RES LAB,SENDAI,MIYAGI 990,JAPAN