2015-2019 年第二十四太陽週期下降期台灣地區電離層特高頻閃爍之變化;Variation of Ionospheric VHF Scintillation during the Declining Phase of Solar Cycle 24 in 2015 – 2019

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題名:	2015-2019 年第二十四太陽週期下降期台灣地區電離層特高頻閃爍之變化;Variation of Ionospheric VHF Scintillation during the Declining Phase of Solar Cycle 24 in 2015 – 2019
作者:	茅雅䪧;Mao, Ya-Chih
貢獻者:	太空科學與工程研究所
關鍵詞:	電離層閃爍;特高頻;飄移速度;滾降斜率
日期:	2022-05-30
上傳時間:	2022-07-13 18:11:56 (UTC+8)
出版者:	國立中央大學
摘要:	使用為期五年2015-2019年特高頻波段之電磁波閃爍資料，觀測資料來源於美國空軍閃爍現象觀測網(SCIntillation Network Decision Aid, SCINDA)的台灣屏東觀測站。研究針對於第二十四太陽週期極大期的第二個高峰後之下降期間，亦即2015-2019年間，將電離層擾動之閃爍指數S4 指數依日變化、季變化、太陽活動變化、閃爍強度進行分類與比較。夜間閃爍發生率在春分與秋分增加至最高，在夏至與冬至減少至最低。春分與秋分之對稱性隨著太陽活動減弱逐漸消失，太陽活動下降期間春季的閃爍出現率高於秋分的閃爍出現率。電離層的夜間閃爍活動，以及東向飄移在太陽活動高度活躍時會非常劇烈；電離層於夏季時有少許的日間閃爍以及西向飄移產生。一般而言，夜間閃爍會在日落後晚上20:00當地時間開始出現，閃爍的年變化則高度依賴太陽活動。強閃爍發生率於太陽極大期最高，於太陽極小期最低，而弱閃爍發生率則在夏季時最高，與太陽週期較無關聯。五年間大部分的夜間閃爍皆觀測於2015年；大部分的日間閃爍則多出現於2016年。強閃爍與弱閃爍事件的時長與太陽週期相關。飄移速度的計算採用完整相關分析方法，可發現飄移速度的消長與太陽週期相關。透過功率頻譜密度分析，得出滾降斜率的變化也與太陽週期相關。飄移加速度則是僅與季變化相關，與太陽週期無明顯關係。;In this study, the faded (or scintillated) signal level and drift measurements were taken by two very-high-frequency (VHF) receivers, situated in one of the SCINDA (SCIntillation Network Decision Aid) stations, (Pingtung, Taiwan), for five years (2015-2019) was utilized to investigate the ionospheric dynamics at the northern rim of EIA. The results show that strong scintillations appear frequently at early nighttime equinoxes during the high solar activity year of 2015, while weak scintillations occur often at early daytime and more frequently at early nighttime in summer without obvious correlation with solar activity levels. In general, nighttime scintillation occurred after 20:00 LT. The annual variation of scintillation is relative to solar activities. The occurrence of strong scintillation is highest in solar maximum and lowest in solar minimum. The occurrence of weak scintillation is highest in summer but not relative to solar activities. Most nighttime scintillation was observed in 2015, and most daytime scintillation was observed in 2016 for five years. The occurrence peak of strong scintillation has happened earlier than the occurrence peak of weak scintillation at nighttime. The duration of weak and strong scintillation events is relative to solar activities. The full correlation analysis can calculate the drift velocity. The vicissitudes of drift velocity are relative to solar activities. The eastward drift dominates the nighttime ionosphere in the solar maximum. The westward drift dominates the daytime in the declining phase of the solar cycle and nighttime in the solar minimum. Stronger scintillations and higher drift velocities are observed in spring and fall. The peak drift of measurements is observed eastward ~50-60 m/s at night and westward during the day. Based on the power spectrum density analysis, the roll-off slope is relative to solar activities. The roll-off slope of power spectrum density is steeper when scintillation is stronger in the solar maximum. The diurnal variation of acceleration is varied by season, not by solar activity. The VHF data set is proven to be valuable and the VHF approach is more cost-efficient for ionospheric studies.
顯示於類別:	[太空科學研究所 ] 博碩士論文

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