2002 年 78 巻 10 号 p. 1009-1014
Recent observations of electric field structures in the high altitude polar ionosphere made by FAST satellite are introduced, placing emphasis on the electric potential drops along the magnetic field lines. Though these potential drops have not been demonstrated by direct measurements of parallel electric field, they have been consistently inferred from measurements of perpendicular electric fields and velocity distribution of plasma particles. There are two types of field structure, the upward and the downward electric field. The characteristic difference between these two structures are discussed, referring to FAST high time resolution observations.