颱風電離層都卜勒效應; Typhoon Ionospheric Doppler Effect

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题名:	颱風電離層都卜勒效應;Typhoon Ionospheric Doppler Effect
作者:	李奕德;I-TE LEE
贡献者:	太空科學研究所
关键词:	都卜勒;電離層;颱風;Doppler;typhoon;ionosphere
日期:	2008-05-22
上传时间:	2009-09-22 09:48:31 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	電離層除受太陽閃焰、磁暴、太陽活動影響外，亦會受到鋒面、雷暴雨和颱風等對流層劇烈天氣之影響而產生擾動。台灣自2005年建立一發射機與四接收站之高頻電離層都卜勒探測系統，以5.26MHz的探測頻率觀測觀測由颱風所造成移行電離層擾亂之都卜勒頻移變化。分析2005-2007年資料，發現於颱風期間大氣波動會引發移行電離層擾亂其都卜勒頻移範圍在0.5-1.5Hz而週期約為16分鐘之擾動現象是為「颱風電離層擾動」。藉由各接收站之時間差與來向角計算方法確認擾動來源與颱風有關，其傳播速度約在50-100 m/s。此外，在颱風登陸台灣本島於離開後的90-120分鐘內，都卜勒探測系統亦會偵測到一個明顯的「颱風登陸與出海之電離層擾動」訊號。其垂直傳播速度約為53.8 m/s，水平傳播速度約為30.7 m/s，週期為20分鐘。 The ionosphere can be perturbed by sever weathers, such as front, thunderstorm, and typhoon (or hurricane). An HF CW Doppler sounding system which consists of 1 transmitter and 4 receiver with a probing frequency 5.26 MHz in Taiwan has been employed to observe variations in the ionospheric Doppler frequency shift (DFS) induced by typhoons since 2005. An analysis of data recorded during 2005-2007 shows that ionospheric DFS fluctuates with 0.5-1.5Hz amplitudes and 16 minute periods during the typhoon periods. An angle of arrival estimation has been applied to analyze time delays observed by the four receiving stations to confirm the waves being the typhoons related and examine the associated propagations. Meanwhile, it is found that when a typhoon landfalls or passes through the Taiwan Island, the ionosphere could be suddenly perturbed during the typhoon eye right on the boundary of land and sea. The vertical and horizontal speeds of the perturbation are about 54 m/s and 31m/s during the typhoon period, respectively.
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