本論文研究發生在地球日側磁層頂的多重穿越事件，採用人造衛星THEMIS分別在兩組不同時間、地點內多次穿越磁層頂所蒐集的觀測資料。將個別穿越事件的資料經過最小差異量法 (Minimum Variance Analysis, MVA)、DeHoffmann−Teller座標 (HT frame)、與Walén Relation分析磁層頂一維結構，以及運用Magnetohydrostatic GS (Grad−Shafranov) 和field−aligned flow (FAF) GS方法重建磁層頂的二維結構。第一組資料為2011年11月26日，UT 18:40:35 ~ 19:27:15發生的六個磁層頂穿越事件。經過分析與重建的結果顯示，磁層頂的形態在這段時間內有著非常劇烈的變化，不論是整體的移動，或是內部的結構分佈，均有一定程度的改變。第二組則是取用2012年1月16日，UT 13:30:58 ~ 13:44:18之間的三次磁層頂穿越事件資料，分析與重建結果則顯示磁層頂形態與結構的變動幅度非常微小。透過檢驗個別事件的磁層頂法線向量，得出衛星每次穿越時，磁層頂結構面的法線方向幾乎一致，顯示衛星在短時間內觀察到的應是同一個磁層頂區域。比較這兩組穿越事件的差異可以得知磁層頂的結構可以在短時間與小區域的範圍內產生劇烈的變動。

We analyze two events of Earth’s magnetopause multiple crossings encountered by THEMIS spacecraft based on the minimum variance analysis (MVA), the deHoffmann−Teller (HT) frame analysis, the Walén relation and the two−dimensional Grad−Shafranov reconstruction method. In particular, for tangential discontinuity (TD) like and rotational discontinuity (RD) like structures, the magnetohydrostatic GS and field−aligned flow (FAF) GS models are adopted, respectively. The results from analyzing the 26 November, 2011 event with six magnetopause crossings show that the structures vary with time. Whereas the analysis results for 16 January, 2012 event with three crossings show that the features are almost the same despite the motion of the magnetopause. The comparisons between these two multiple crossing events are made.

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