The DE 2 satellite observed electric field fluctuations on the topside of the nighttime midlatitude ionosphere. They extended several hundred kilometers in the latitudinal direction with wavelengths of several tens of kilometers, and their amplitudes were a few millivolts per meter. Such fluctuations were often observed at magnetically conjugate points in the northern and southern hemispheres. These electric field fluctuations are perpendicular to the geomagnetic field. They are not accompanied by any significant plasma depletion or electron temperature v•riations. Magnetic field fluctuations are sometimes observed simultaneously with electric field fluctuations. We interpret that these fluctuations are caused by fieldaligned currents which flow from the ionosphere in one hemisphere to the conjugate point in the other hemisphere. The power spectrum of these midlatitude electric field fluctuations follows a power law of the form Power c• f-•, with the spectral index n of 3.5 to 4.5, which is steeper than that of the electric field fluctuations in the high-latitude ionosphere or in the equatorial ionosphere. This phenomenon may be related to other ionospheric phenomena, for example, the F region field-aligned irregularities or spre•d-F, observed by ground-b•sed methods such •s the MU r•d•r, but the relationship is not clear. (MEFs), which often appear simultaneously at magnetically conjugate points, and discuss the relation between these electric field fluctuations and the F region FAIs. In situ observations of the midlatitude ionospheric electric field by satellites play an important role in understanding the mechanism of the ionospheric irregularities which have been observed by ground-based techniques. Observation The DE 2 satellite flew in polar orbit at about 250-km to 900-km altitudes. It observed the ionospheric electric field at midlatitudes from August 1981 to February 21,439 21,440 SAITO ET AL.' MIDLATITUDE ELECTRIC FIELD FLUCTUATIONS a sampling rate of two samples per second [Krehbiel et al., 1981]. Vector magnetic field data were obtained by dinate (SPC) system, where the x axis is in the direction of the satellite velocity and the y axis is downward, with the z axis completing a right-handed coordinate system.

Seasonal and year‐to‐year variations of geomagnetic Sq field were examined using the global equivalent current system for one solar cycle from 1980 to 1990. It was confirmed that the Sq current intensity is about half in solar minimum of that in solar maximum and its year‐to‐year variation is relatively smooth for each month. At 0200 UT, vortices in the winter and summer hemispheres shift to the afternoon and morning side, respectively, but with phase delay by about 1 or 2 months. On the contrary, at 1400 UT the northern vortex is located in the morning side of the southern vortex in most months of all years, and seasonal variation of the location is not so clear. As for the morphology of the current system, it was found that there are only two types in the shape of the Sq current system at 0200 UT. That is, it shows “northern summer type” from April to September and “northern winter type” from October to March, and there is no “equinox type,” and it clearly differs in March from that in September. This feature is similar to that of the seasonal variation type of the tidal winds in the upper mesosphere.

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Results obtained in the initial experimental phase of Heliotron J are reported. Electron beam mapping of the magnetic surfaces at a reduced DC magnetic field has revealed that the observed surfaces are in basic agreement with the ones calculated on the basis of the measured ambient field around the device. For 53.2 GHz second harmonic ECH hydrogen plasmas, a fairly wide resonance range for breakdown and heating by the TE02 mode has been observed in Heliotron J as compared with that in Heliotron E. With ECH injection powers up to ≈ 400 kW, diamagnetic stored energies up to ≈ 0.7 kJ were obtained without optimized density control.

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