電離層探測儀與全球定位系統聯合觀測電離層F層電漿密度不規則體

The Concurrent Observations of the Ionospheric F-region Plasma Density Irregularity Using Ionosonde and Global Positioning System

陳瑋陞(Wei-Sheng Chen)

指導教授 ： 劉正彥

國立中央大學/地球科學學院/太空科學研究所/博士(2007年)

摘要

電離層中之電漿密度不規則體會影響電磁波的傳播，其中電離層探測儀所觀測到的散狀F層，以及全球定位系統之相位擾亂均屬於此一範疇。利用全球定位系統之相位擾亂觀測量研究電離層中之電漿密度不規則體開始於90年代初期。但相關的研究並不充裕，且相位擾亂的變化模式也並不完全清楚。另一方面，電離層探測儀之散狀F層現象已研究了超過50年，相關的現象已有一定之理論基礎。是故本篇論文利用上述兩種技術共同觀測不同緯度之電漿密度不規則體。透過比對兩種技術之觀測結果，以期對於相位擾亂的變化模式有更深的認識，並探討其中隱含之物理意義。研究的範圍囊括磁赤道地區、赤道異常區以及中緯度地區。觀測時間則選在1999年至2000年，此時為太陽活動極大期。研究方法為統計散狀F層與相位擾亂的發生機率，比較兩者之月變化與日變化。
在磁赤道地區，觀測地點為祕魯。研究結果顯示，春秋季及夏季是散狀F層與相位擾亂的好發期，其中強烈之相位擾亂集中在春秋季。此外，電漿密度不規則體在前半夜的高度分布範圍較廣，而相位擾亂在前半夜也較強烈。整個散狀F層與相位擾亂的發生機率月變化與日變化符合漂移速度之變化。此研究也證實相位擾亂與電漿密度不規則體的高度分布範圍有關。
在赤道異常區，觀測地點為台灣。觀測結果顯示，散狀F層主要分布在春秋季的前半夜及夏季的後半夜。相位擾亂則集中在春秋季與夏季的子夜附近，且幾乎沒有強烈的相位擾亂出現。赤道異常區的變化顯示，由於電漿密度不規則體沿磁力線分布的特性，在磁赤道地區的高度分布範圍直接影響赤道異常區的相位擾亂大小。
在中緯度地區，觀測地點為武漢。研究結果顯示，散狀F層與相位擾亂僅出現在夏季。散狀F層主要分布在子夜之後，相位擾亂則分布在子夜附近。中緯度地區同樣沒有強烈的相位擾亂出現，且散狀F層與相位擾亂的月變化與赤道異常區的觀測結果不同，顯示中緯度地區的電漿密度不規則體產生機制與磁赤道地區無關。此外，與其它的文獻比較後發現，中緯度地區的電漿密度不規則體可能與電離層行進式擾動有關。

關鍵字

電漿密度不規則體 ； 相位擾亂 ； 電離層 ； 全球定位系統 ； 電離層探測儀

並列摘要

The plasma density irregularities, which exist in ionosphere, can influence the propagation of radio waves. The ionosonde spread F and GPS phase fluctuations belong to this kind of phenomena. The observation of GPS phase fluctuations started from 1990s. However, the amount of research of this parameter is still few, and its occurrence pattern is not studied in detail. On the other hand, the ionosonde spread F has been investigated for over 50 years, and the behavior of its variations is well known. In this dissertation, we make use of the two different instruments, the ionosonde and the GPS, to observe the irregularities in different latitudes, concurrently. By comparing the two observations, we want to study about the variations of GPS phase fluctuations, and to understand the physical meaning behind the variations. The observation have been conducted at the geomagnetic equator, equatorial ionization anomaly region, and mid-latitudes during 1999 to 2000. We calculate the relative occurrences of spread F and GPS phase fluctuations, and then compare their monthly and daily variations.
The observations from Peru have been used for the study at the geomagnetic equatorial region. The results show that the spread F and the GPS phase fluctuations frequently occur during equinox and summer, however, the intense GPS phase fluctuations are more often in equinox. Moreover, the irregularities have larger altitudinal distribution range in the pre-midnight hours, and the GPS phase fluctuations are also more intense in this period. The variation patterns of spread F and GPS phase fluctuations can be explained based on ExB drift variation, and the comparison also confirm that the GPS phase fluctuations are related to the altitudinal range of the distribution of irregularities.
In Equatorial ionization anomaly region, the observations were carried out in Taiwan. In this region, the spread F mainly occurs in the pre-midnight period in equinox, and in the post-midnight period in summer. The GPS phase fluctuations have high occurrences around the midnight in equinox and summer. Moreover, there is almost no intense GPS phase fluctuations. Since the irregularities are magnetic field aligned, their altitudinal distribution range at the geomagnetic equator directly influence the intensity of GPS phase fluctuations at the equatorial ionization anomaly region.
The data from Wuhan is selected to study the variations at the mid-latitude region. The observations show that the spread F and the GPS phase fluctuations have high occurrences in summer. The spread F mainly occur in the post-midnight period, and the GPS phase fluctuations peak around midnight. The observations also indicate the absence of intense GPS phase fluctuations at Wuhan. The monthly variations of two instrument observations show that the pattern at Wuhan is very different from that at the equatorial ionization anomaly region. This result suggests that the physical mechanism of irregularities in the mid-latitude region is unrelated with the processes at the geomagnetic equatorial region. Moreover, it seems that the irregularities in mid-latitudes are related to the traveling ionospheric disturbances.

並列關鍵字

Ionosphere ； Ionosonde ； Phase fluctuations ； Irregularity ； GPS

參考文獻

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