在本篇研究中，我們探討西密斯衛星於磁層內的觀測之離子環狀速度分布函數隨空間之變化。數據方面使用了固態望遠鏡紀錄的離子速度並利用西密斯網站上提供的軟體畫出速度分布圖，找出具有環狀速度分布之事件，並利用衛星軌道分析器(TIPSOD)比對時間，之後記錄這些事件的觀測位置。
我們先以不同的參數記錄發生環狀速度分布的位置，並且藉由計算出來的機率來找出可能因為位置不同而較容易發生環狀分布的區域。所使用的參數為地球的徑向距離、麥爾基韋恩L參數(McIlwain L-parameter)、磁緯度、以及GSM 座標。 我們首先使用GSM座標系統來紀錄發生離子環狀速度分布的位置，並計算出發生環狀分布的機率；接著再配合徑向距離、L參數、磁緯度再次分析位置以及機率，之後我們利用GSM座標把觀測範圍依時區不同而分成四個區域:晨側 (03-09)、日側 (09-15)、黃昏側 (15-21)、及夜側 (21-03)等再分析其發生機率。從觀測事件的位置來看，離子環狀速度分布位置大部分落在距離地球兩個到四個半徑之間的區域，並且在每一區域都被觀測到。從發生機率來看，離子環狀速度分布事件發生在離磁赤道高度等於一個地球半徑的區域內的區域較高；其中在夜側的特定區域(L=3,磁緯度=0°到10°)發生環狀分布的機率較高。但若不考慮磁緯度(衛星觀測範圍為正負20°)的狀況下每一側發生環狀分布的最高機率大約為30% 且皆發生在靠近 L=3 的區域。而在每一側之L = 2 至L = 4的區域中，環狀分布的發生機率沒有太大差異。

In this study, we observe the ion ring velocity distributions in the magnetosphere by THEMIS satellite because of the low magnetic latitude orbits. We use Solid State Telescope (SST) to obtain the data and record the locations of the ring distributions in the magnetosphere at the distance less than 12 radii of the Earth.
In our observations, we use radial distance, McIlwain L-parameter, magnetic latitude, and locations in GSM coordinates to analyze locations and calculate the occurrence probabilities of ion ring velocity distributions with the locations. We start to trace the time that ion ring distributions occurred and obtain to the corresponding satellite locations using by SSC 4D Orbit Viewer (TIPSOD), and calculate the probabilities in space. We also characterize the locations by regions, including dawn, dayside, dusk, and nightside, and discuss the occurrence probabilities of ion ring velocity distributions based on radial distance or McIlwain L-parameter and magnetic latitude. Ion ring distributions most often occur near and around the Earth (2RE to 4RE). The probabilities in nightside with specific region (L = 3, MLAT = 0° to 10°) are higher. The maximum value of probabilities is about 30% at the L=3 magnetic field lines. The probabilities of ring distributions have no big difference on each side when we consider L from 2 to 4.

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