用華衛一號觀測資料研究離子沿磁場飄移速度之變化與成因; The reasons and variations of ion drift parallel to the B-field using ROCSAT-1 observation

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题名:	用華衛一號觀測資料研究離子沿磁場飄移速度之變化與成因;The reasons and variations of ion drift parallel to the B-field using ROCSAT-1 observation
作者:	許慶涵;Ching-Han Hsu
贡献者:	太空科學研究所
关键词:	赤道密度異常;磁暴;電漿泡;中性風;離子飄移;magnetic storm;bubble;EIA;neutral wind;ion drift
日期:	2004-06-23
上传时间:	2009-09-22 09:46:27 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本文藉由中華衛星一號 (ROCSAT-1) 上之酬載’電離層電漿電動儀(IPEI)’所量測到的三維離子速度資料，來探討離子飄移沿磁場方向速度分量的變化情形及驅動變化的重要因素。由觀測所得到的結果可以明顯看出平行磁場離子飄移速度大小與方向受到季節中性風的影響。在沒有電漿泡與赤道異常(EIA) 現象發生的區域，當北半球為冬季時離子沿磁場往北運動，而當北半球為夏季時則離子往南運動，另外在春秋季時則沒有明顯偏向任何一方運動，是為春秋並沒明顯的季節中性風可以影響。當有電漿泡與赤道異常現象發生的區域則不受季節的影響。在EIA區高緯側常見離子的運動沿磁力線極向傳播與赤道噴泉效應所預期相符。而下降電漿泡的平行離子飄移也是極向的，而飄移速的變化則會很劇烈。因赤道異常高峰區常座落在南北磁緯度11~25度範圍內，因此在這些緯度，常可觀測到離子飄移與季節中性風方向相反的情形。另外當磁暴發生時，觀測到出現在北半球跟南半球電離層的平行離子飄移皆往赤道方向運動的情形，當與安靜狀態做比較時，更可發現磁暴發生時與安靜狀態時有明顯的差異，可知離子受到磁暴時在極光區所產生的向赤道方向中性風的影響明顯比季節中性風的影響來的大。 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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