摘要 本篇論文利用中華衛星一號(ROCSAT-1)以350傾角飛行的特性，分析電離層電漿電動效應儀在西元兩千年太陽活動極大期，所觀測到的離子密度及飄移速度資料，以探討在600公里高的頂部電離層發生的赤道電漿密度異常現象(EIA)，藉由統計分佈在南北磁半球的最大電漿密度位置(Double –peak EIA crest)，找出Crest 的分佈如何隨著不同的季節、地方時、經緯度和地磁場方向而變化。在此我們特別強調EIA結構與經度之關係，因為關於赤道電漿密度異常現象一直以來都甚少有論文觸及。 統計上發現在全球春秋兩季觀測上出現(Double crests)的機率大於夏冬兩季；而以地方時來說，在13:00到15:00有最大的觀測次數；在隨著地理經緯度分佈上，得到不同的經度範圍的EIA crest 其產生在緯度上的位置並不相同。因此本論文引入水平中性風沿著磁力線對電漿飄移所產生的作用，與赤道噴泉效應產生加成或是抵銷的影響，來進一步說明南北半球EIA的不對稱性，也解釋了EIA crest的緯度分佈隨經度而異的原因。研究中也得到在固定經度範圍(900E到1200E內)，大約於地方時14左右EIA crest出現的緯度位置最偏離磁赤道，此結果與低緯電離層斷層掃描網(LITN)的觀測吻合。 Abstract Due to the unique 35-degree orbital inclination of ROCSAT-1 and 100% duty-cycle operation of the Ionospheric Plasma and Electrodynamics Instrument (IPEI) , the ROCSAT-IPEI has collected a large set of ion density and velocity data over the equatorial ionization anomaly (EIA) region. In this thesis, we utilize the data acquired from IPEI in the year of 2000, which is during the solar maximum, to study the EIA phenomenon in the topside (600km altitude) ionosphere. For the convenience of statistical analysis, we define an EIA event as that the ion density maximum (crest) can be identified in both magnetic hemispheres along a satellite orbit (i.e., Double- Crest EIA). We investigate how the distribution of the EIA events varies with season, local time, latitude, longitude as well as geomagnetic configuration. We emphasize the longitudinal dependency of the EIA structures since such dependency of the EIA phenomenon has not been well explored. From the statistical analysis, we found that the EIA events most often occurred during equinoxes, and less often during solstices. Most of the EIA events were found in the local time sector between 13:00 and 15:00. The latitudinal distribution of the EIA crests varies with geographic longitudes. The hemispheric asymmetry was found in the latitude locations of the EIA crests. These statistical results can be explained in terms of Fountain effect that was triggered by the upward ion drift and modulated by the horizontal neutral wind along the geomagnetic field lines. In addition we find that the EIA crests are located at the highest latitude around the 14:00 hour local time in the longitude sector between 900E and 1200E. The observation is consistent with that observed by the Low-latitude Ionospheric Tomography Network (LITN).
