Measurements of Ionospheric Electric Fields with Antarctic Sounding Rockets S-210JA-24 and 25 (b. Electric Fields and Current System) (Proceedings of the First Symposium on Coordinated Observations of the Ionosphere and the Magnetosphere in the Polar Regions (Part I))

DC and AC (8-110 Hz) electric fields were observed in the auroral ionosphere up to 120 km with spherical double probes on board the sounding rockets S-210JA-24 and 25 at Syowa Station. The rockets passed close to auroras. The DC electric fields observed during substorms at magnetic midnight are composed of the height-independent electric field of about 20 mV/m and the local electric field of up to 30 mV/m. The former electric field is the large scale electric field generally existing in the auroral ionosphere, and the latter local electric field will be the effect of space charges produced by precipitating auroral particles, peaking at the heights between 100-115 km. Strong AC noises were observed in the limited altitude range of 96-112 km during both the ascent and the descent. The noise frequencies varied with altitude and were ranged between 20 and higher than 110 Hz. The noises appeared in the direction perpendicular to the DC electric field. These characteristics suggest that the noises might be generated by plasma instability in the ionospheric current layer.