運用西蜜斯衛星資料研究低頻帶升調合唱波的重複發生週期之分布; An analysis of distributions of the repetition period of lower-band rising-tone chorus waves using THEMIS observations

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题名:	運用西蜜斯衛星資料研究低頻帶升調合唱波的重複發生週期之分布;An analysis of distributions of the repetition period of lower-band rising-tone chorus waves using THEMIS observations
作者:	謝怡凱;Hsieh,Yi-Kai
贡献者:	太空科學研究所
关键词:	合唱波;重複發生週期;內磁層;Chorus waves;Repetition period;Inner magnetosphere
日期:	2013-07-01
上传时间:	2013-08-22 11:41:43 (UTC+8)
出版者:	國立中央大學
摘要:	合唱波在地球內磁層產生，受高能電子漂移路徑影響，其主要發生在電漿球層外、磁層頂以內的近磁赤道區域，合唱波產生之後會沿著磁力線傳播，並會與當地的電子進行交互作用，進而加速電子。連續出現的分立波元是合唱波的特徵，分立波元出現的時間差稱為重複發生週期。本研究中使用西蜜斯衛星的高時間解析度磁場資料觀測資料來探討低頻帶升調合唱波的重複發生週期在空間分布上的變化，並研究重複發生週期與相關磁層中背景參數之關係。研究發現在夜側和晨側區域的合唱波重複發生週期分布較集中，平均值也較小，分別為0.56和0.54秒，而日側和昏側區域的重複發生週期分布較廣，週期有長有短，其平均值約為夜側和晨側的2倍。將重複發生週期與背景電漿參數比較後，發現電子溫度是影響各區域重複發生週期變化的因素之一，當電子溫度越低時，該區域的重複發生週期分布越廣。本研究的統計結果將有助於研究合唱波與電子之間交互作用的模擬。 Whistler-mode chorus waves most likely occur in the dayside, dawnside, and nightside sectors of the inner magnetosphere owing to the co-location of the drift trajectories of energetic electrons. When the chorus waves are excited by electron anisotropy in the minimum magnetic field region, they propagate along the field lines, possibly interacting with charged particles under some resonance conditions. The most noticeable property of chorus waves is discrete elements. The repetition period of chorus waves is defined as the generation time delay between two consecutive discrete chorus elements. Here we utilize in situ high-resolution magnetic fields from the THEMIS mission to obtain distributions of the repetition period of chorus elements for various local time sectors. These distributions have a peak at lower repetition periods and a long tail at higher repetition periods. We find that the average repetition periods for the dawnside (3 < MLT < 9) and the nightside (21 < MLT < 3) sectors are 0.54 and 0.56 s, respectively. The repetition periods for the dayside (9 < MLT<15) and the duskside (15 < MLT < 21) sectors are about two times of those for the dawnside and nightside sectors. Temperature might be the factor that affect the variability range of repetition period. The variability range of repetition period is wider when the resonating electrons have lower temperature. The distributions derived from this study are important to a modeling of wave-particle interactions for radiation belt electrons.
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