| Summary: | 碩士 === 國立中央大學 === 太空科學研究所 === 92 === This thesis uses the three dimensional ion velocity data available from the ionospheric plasma and electrodynamics instrument (IPEI) onboard the ROCSAT-1 satellite to study the variations of ion drift parallel to the geomagnetic field lines, and the possible causes of these variations. From the observations we found that the magnitude and the direction of parallel ion drifts are strongly affected by seasonal neutral wind. In the regions where the equatorial ionization anomaly (EIA) crests and the plasma bubbles were not observed, the ions drifted northward when the northern hemisphere was in winter, on the contrary, the ions moved southward when the northern hemisphere was in summer. During the equinoxes, the parallel ion drift is small because there is no obviously seasonal neutral wind can affect it. Near the regions where the EIA crests were observed (11o-25o MLAT), the ions move along the magnetic field lines toward the geomagnetic poles. Such pole-ward ion drifts are consistent with those expected from the equatorial fountain effect. In the plasma bubble regions, the ion drifts were also pole-ward. They were often very strong and had large variations. In both regions, the parallel ion motions are dominated by the pole-ward diffusion, but not the seasonal neutral winds. During the magnetic storms, we observed that the ions drifted equator-ward from both hemispheres. When we compare these drifts with those during the quiet time, we find that the storm-time field-aligned ion drifts are so much different from the quiet time ion drifts. Because of it, we conclude that the storm-time equator-ward wind from the auroral region has stronger effects than those of the seasonal neutral wind on the parallel ion motions.
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