磁層頂邊界層的概念首次由Chapman 與Ferraro 所提出，並以壓力平衡的觀點切入討論。當太陽風電漿粒子流自太陽傳播到地球時，其動壓會與地球磁層本身具有的磁壓相互競爭而達到平衡。Spreiter 等人由流體力學理論導出一磁層頂邊界壓力平衡關係式，描述了在磁層頂邊界的壓力平衡情況，K Ps =4 f 2 Pm，等號左邊Ps 為太陽風動壓，K 為太陽風壓力有效轉換因數，等號右邊Pm 為在磁層頂邊界處的純磁偶極磁場磁壓，f 為地球磁層磁場被太陽風壓縮因數。以前太空科學研究人員對於磁層頂處壓力平衡情況的研究，多著力於地球磁層各處對於磁層頂內側處磁壓的貢獻之分析討論，而將太陽風動壓有效轉換因數K 視為一常數。目前尚無研究報告是透過實際的衛星資料，針對因數K 而分析討論其變化情形與其所受影響的因素。在本研究中，我們將使用西蜜斯號衛星任務 (THEMIS, Time History of Events and their Macroscopic Interactions during Substorms) 之資料，計算因數K 且對其進行同步時序的分析研究。研究中，我們將選取2007~2008 年的西密斯號衛星任務任何兩顆衛星分別同時位於行星際空間和靠近磁層頂的磁鞘區域之事件，計算太陽風動壓有效轉換因數K，並與太陽風參數，包括太陽風電漿密度、太陽風電漿溫度、太陽風磁場強度和太陽風磁場極化方向等，進行比對分析討論，所得到的結果將可對影響太陽風動壓有效轉換係數K 變化的因素有更進一步的釐清，並進一步地提升對於磁層頂邊界壓力平衡情況的瞭解， The concept of the magnetopause boundary layer of the Earth was first brought up by Chapman and Ferraro under a consideration of pressure balance. When the high-speed solar wind propagates from the Sun to the Earth, it compresses the Earth’s magnetosphere and its total pressure is balanced with the total pressure of the magnetosphere. With gasdynamics, Spreiter and the others derived an equation to describe the state of pressure balance at the magnetopause, K Ps =4 f 2 Pm, where Ps represents the dynamic pressure of the solar wind and K is the effective conversion factor of the solar wind dynamic pressure under an influence of the magnetosheath; and Pm represents the magnetic pressure of the pure dipole magnetic field at the position of the magnetopause and f is the compression factor of the Earth’s magnetosphere by the solar wind with respect to the dipole magnetic field. In the past, the space scientists paid most of their attention on the compression factor, and considered K as a constant. Less research has concentrated on the variations of K and solar wind parameters that affects K. In this research, we will conduct a simultaneous analysis on K using the data set from THEMIS mission (THEMIS, Time History of Events and their Macroscopic Interactions during Substorms). From THEMIS data for 2007 and 2008, we will select events with which any two of the five probes separately stayed at the region of the solar wind and the region just outside the magnetopause, therefore, we can directly calculate K with simultaneous observations. Meanwhile, we will relate the calculated K to the solar wind plasma density, temperature, the magnitude and orientation of interplanetary magnetic fields. Through this proposed research, we can have further understanding into the parameters that control the effective conversion factor K and the pressure balance at the magnetopause. 研究期間 : 9808 ~ 9907
