臺灣博碩士論文加值系統

電漿團是一種產生於夜間電離層的現象，電漿密度較其背景電漿高的不規則體。電漿團首次在1981年被Hinotori衛星所觀測到，但是它的產生機制至今仍然沒有定論。為了對電漿團有進一步的瞭解，我們設計了一個自動搜尋程式，在中華衛星一號(福衛一號)1999至2004年期間太陽活動逐漸降低時期所觀測的資料中來尋找電漿團的產生分佈情形。我們分別對電漿團隨經度、dip-latitude、當地時間、季節、磁場擾動與太陽活動的產生機率作統計分析。在經度分佈上，電漿團的產生於 ±15° dip-latitude之間並沒有明顯的變化，而這與產生在磁赤道附近的電漿泡會隨著經度有所變化的情形並不相同，也因此證明瞭電漿團和電漿泡應該有者不同的產生機制。在dip-latitude的分佈上，我們發現電漿團在 ±15° dip-latitude之間有著最小的產生機率，且隨緯度增高而增加。在當地時間的變化上，電漿團的產生機率約在午夜時有最大值，並於午夜過後開始緩慢減少，直到04 LT後快速下降。在季節上的變化，電漿團的產生機率在南北半球上，均在夏、冬至時較高，而在春、秋分時較低。除此之外，南北半球的夏至時都有最高的電漿團產生機率。在磁擾動時期(Kp≧3)，電漿團的產生機率只在午夜過後有些微的變化，也就是說磁場擾動並沒有對電漿團的產生有太大的影響，這個特徵也和電漿泡有所不同，因為在磁場擾動較大的時期，電漿泡會有較高的產生機率 [e.g. Watanabe and Oya, 1986]。在太陽活動對電漿團的影響上，我們發現電漿團似乎在太陽活動較低時，會有較高的產生機率，這個情況也和電漿泡所產生的現象相反 [e.g. Su et al., 2006; Watanabe and Oya, 1986]。

A plasma blob is an irregularity structure with density enhancement above the background in the nighttime ionosphere. The first report of the plasma blob observation was made with Hinotori in 1981, but the occurrence mechanism of the plasma blob is still unknown. An auto-search program is designed to find the plasma blob occurrence distribution in the ROCSAT-1 data taken during the high to moderate solar activity years of 1999 to 2004. The result of the plasma blob occurrence probability is presented in the distributions in longitude/dip-latitude/local-time/season/magnetic activity/solar activity. In the longitude distribution, although the plasma blob occurrence probability has a longitudinal variation, there is no apparent variation between ±15° dip-latitude, which is very different from the plasma bubble occurrences, and this is evident that the plasma bubble and plasma blob have different occurrence mechanisms. For the dip-latitude distribution, we find that the plasma blob has a minimum occurrence probability from -15° to 15° in dip-latitude and increases toward the higher latitudes. For the local-time variation, the plasma blob occurrence probability has a maximum around midnight, and it decreases slowly after midnight and decreases rapidly after 04 LT in most seasons. For the seasonal variation, the occurrence probability of the plasma blob is larger at solstice than at equinox. Furthermore, it has the maximum occurrence probability in both northern and southern hemispheres during the June solstice. During magnetic disturbed periods (Kp≧3), the plasma blob occurrence probability only indicates a small variation after midnight. That is, the magnetic disturbance seems to have little effect on the plasma blob occurrences. This is different to the equatorial bubbles in which the occurrence probability will increase after midnight during the magnetic disturbed time [e.g. Watanabe and Oya, 1986]. For the solar activity effect, the plasma blob seems to have more occurrences during low solar activity years which is opposite to the occurrences of the equatorial bubble [e.g. Su et al., 2006; Watanabe and Oya, 1986].

摘要 i
Abstract ii
誌謝 iii
List of Tables iv
List of Figures vi
Chapter 1 Introduction 1
1.1 ROCSAT-1 1
1.2 The Plasma Irregularities in the Postsunset Ionosphere: Plasma Bubbles
versus Plasma Blobs 1
1.3 The Purpose of the Current Study 3
Chapter 2 Automatic Search of Plasma Blob Occurrences 4
2.1 Auto-search Scheme 4
2.2 Results of the Plasma Blob Selections 7
Chapter 3 The Plasma Blob Occurrence Distributions 9
3.1 Global Distribution 9
3.2 Dip-latitude Distribution 13
3.3 Local Time Dependence 15
3.4 Monthly Variation 18
3.5 Occurrence Variation Due to Magnetic Conditions 19
3.6 Comparison of the Plasma Blob Occurrences with Solar Activity(F10.7) 23
Chapter 4 Discussion and Conclusions 26
4.1 Discussion 26
4.2 Conclusions 28
Appendices
Appendix A Auto-search Program 29
A-1 Results of Using Different Criterion Values 29
A-2 Wrongly Selected Examples Due to the Existence of Equatorial
Bubble 33
A-3 Results of Auto-search Program with Detrended Process 34
Appendix B Perkins Instability 36
Appendix C Es Layer Instability 40
Appendix D Coupling of the Perkins Instability with the Es Layer Instability 44
References 48

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