利用福衛一號觀測資料對電離層快速上升電漿泡之研究; Study of Fast Rising Plasma Bubbles Using ROCSAT-1/IPEI Data

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題名:	利用福衛一號觀測資料對電離層快速上升電漿泡之研究;Study of Fast Rising Plasma Bubbles Using ROCSAT-1/IPEI Data
作者:	謝明杰;Ming Hsieh
貢獻者:	太空科學研究所
關鍵詞:	赤道;電漿泡;快速上升;福衛一號;觀測資料;電漿;Data;Fast rising;plasma.equator;ROCSAT 1;plasma bubble
日期:	2005-07-19
上傳時間:	2009-09-22 09:46:15 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文利用福衛一號(ROCSAT-1)上的電離層電漿電動儀(IPEI)在西元2000年所量測的電離層電漿密度及速度資料，統計分析上升速度超過400 m/s的電離層電漿泡(Fast Rising Bubble)發生機率在不同KP下隨月份季節、地理(磁)位置、當地時間的變化以及空間結構尺度大小的統計。更利用IPEI特有的高解析度(1024 Hz)資料，分析四個具有代表性的快速上升電漿泡的波譜特性。就整體而言，FRB在春秋兩季最常發生，且在大西洋區附近發生的機率最高。而它們的空間結構尺度，隨著上升速度越快，呈現小尺度結構的機率越高。電漿泡上升速度的大小對於其隨月份季節、當地時間和地理(磁)位置的分佈影響不大，但和地磁的擾動有關係。當磁場擾動小時，所觀測的電離層FRB事件大多發生在入夜之後18點至21點之間，而發生的位置大多集中在磁赤道附近。而當磁場擾動大時，午夜至日出之間FRB的發生機率大增，且發生位置不受限於磁赤道地區。其中在幾個磁暴發生時間所觀測到的FRB大多具有小尺度密度變化大，上升速度達1000 m/s或更高，而且散佈空間很廣的特性。這些特性可能和磁暴時產生的東向擾動電場的分布有關。從研究四個FRB事件的波譜特性得知，大部分電漿泡離子密度的波譜功率隨波數增加而減少的趨勢則遵循了指數律( )。統計的結果顯示中尺度(本文定為波長在1 km~100 m)密度波的平均波譜指數(n1)分別在地磁安靜期為-1.87，在磁暴期間為-1.62。小尺度(本文定為波長<100 m)波的平均波譜指數(n2)分別在安靜期為-5.16而在擾動期為-4.66。相對的，在FRB速度的波譜型態則變化較大。尤其當磁暴發生時，在超速(例 V >2000 m/s)上升電漿泡的速度波譜上，我們往往發現波譜功率隨波數變化並不依循指數律，而且常可見到窄波帶小尺度波主宰了波譜結構。造成這些波譜特性的背後機制將是我們下一歩要研究的課題。 In this paper, we use the plasma density and velocity data from the IPEI payload onboard the ROCSAT-1 satellite in 2000 to statistically analyze the occurrence percentage of Fast Rising Bubble (FRB) with upward velocity > 400 m/s. We group the FRB events under different Kp conditions and examine the dependencies of the percentage occurrence on season, geographical location, local time, and scale size of the FRB structures. We also study the spectral characteristics of four cases of FRB event by using the high-resolution plasma data (1024 Hz) from IPEI. According to the analysis results, the occurrence percentage of FRB is higher in the spring and fall seasons and also near the Atlantic Ocean longitude sector. The percentage of observing small-scale structure is increased as the rising speed of the bubble increases. The rising speed of the bubbles is not strongly affect the seasonal, local time, and geographical distributions of the FRB events, but is related to the geomagnetic disturbances. During the quiet time, the FRB events occur more often between 18:00 LT and 21:00 LT, and the locations of the FRB events are near the geomagnetic equator. During the storm time, the occurrence percentage of FRB increases in post midnight hours, and the presence of FRB is not restricted in the geomagnetic equator region. We have examined some FRB events during the storm time. The results show some interesting properties that the plasma density of FRB is highly variable and dominated by small-scale structures with high rising speed ( 1000 m/s) and that the FRB widely spreads in the space. Those properties are probably caused by the perturbed eastward electric fields during the storm time. According to the spectral analysis of four FRB events, we found that most of the spectral power density (PSD) of the ion density decreases with increasing wave number, which is consistent with the power law ( ). The statistical result shows that the average spectral indexes (n1) of the middle-scale (1 km ~ 100 m) density wave are -1.87 and -1.62, respectively, for the quiet time and for the storm time, while for the small-scale (< 100m) density wave the indexes (n2) are -5.16 in the quiet time and -4.66 in the storm time. The characteristics of the FRB velocity spectrum are quite different from the density wave. Specifically, during the storm time, we find that the spectrum of the FRB with speed greater than 2000 m/s does not obey the power law and the small-scale waves dominate the spectral structures. The mechanisms of these spectral features are an interesting subject for future study.
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