大氣層閃電對頂部電離層電漿不規則體的相關性; On the Relationship between Atmospheric Lightning and Topside Ionospheric Irregularity

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Title:	大氣層閃電對頂部電離層電漿不規則體的相關性;On the Relationship between Atmospheric Lightning and Topside Ionospheric Irregularity
Authors:	林沐諺;Mu-Yan Lin
Contributors:	太空科學研究所
Keywords:	閃電;頂部電離層;電漿不規則體;lightning;topside ionospheric;irregularity
Date:	2008-06-27
Issue Date:	2009-09-22 09:48:56 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本論文利用福爾摩沙衛星一號（ROCSAT-1）上的電離層電漿及電動效應儀（IPEI）在太陽最活躍的西元2000年冬季和2001年夏季所量測的電離層離子濃度及速度資料，配合熱帶地區降雨測量任務衛星（TRMM）上的閃電影像偵測儀（LIS）所觀測到的閃電資料進行分析，以研究大氣層中的閃電事件對頂部電離層電漿不規則體之影響。首先分析兩者在空間之統計分佈相關性，作者發現頂部電離層電漿不規則體的好發區在北半球冬季時，主要集中在南美洲與大西洋上空，與閃電現象好發區之一幾乎吻合，但閃電的好發區亦存在於非洲及澳洲。從海陸統計的情形來看，電漿不規則體分佈在海洋上佔多數，閃電卻主要發生在陸地上，不過若依閃電強度之統計分佈來看，作者發現海洋上產生強度較強的閃電機率比全球閃電強度分佈情形略高，因此推斷頂部電離層電漿不規則體的產生與強閃電好發區有關。進一步本論文特別挑出兩個閃電現象與頂部電離層電漿不規則體幾乎時空吻合的事件以作細部分析。事件(Ⅰ)發生於 2001年2月2日 18:26~18:33 UT︰ TRMM觀測到閃電現象持續約兩分鐘後，有小區域電離層電漿泡在閃電區東南方被ROCSAT-1觀測到。波譜分析1024Hz取樣的離子密度及離子速度資料，顯示存在有20m~1000m波長的電漿波，若將離子速度擾動轉成電場擾動而估計出之電場振幅約為2.5mV/m，這與閃電電磁脈衝波傳遞至高200km之電場大小相去不遠。此外，作者也研究50m~120m波的偏極性而發現它們是右旋橢圓極化。事件(Ⅱ)發生於2001年1月26日 00:36~00:51 UT︰作者發現ROCSAT-1在這段時間裡，閃電前觀測到的電漿不規則體濃度變化沒有相對應的垂直漂移速度變化，在閃電後才觀測到電漿不規則體呈現有小尺度相對應的垂直漂移速度。閃電發生後的電漿泡之波譜則顯現波色散現象，即先見短波後見長波。不論從統計觀點或個案分析來看，作者可以推斷伴隨強閃電的電磁脈衝波可以傳至頂部電離層而局部影響它的密度與速度結構，但可能不是觸發大區域F層電漿不規則體的主要因素。 Combining ion density and velocity observations from the ROCSAT-1 IPEI payload with the lightning data from the TRMM LIS payload during the solar maximum years of 2000 winter and 2001 summer, we investigate the relationship between atmospheric lightning and topside ionospheric irregularity. Statistically, during the northern winter the topside ionospheric irregularities mainly occur in South America and the Atlantic Ocean, which collocated well with one of the most probable lightning regions, but the lightning events were also frequently found in Africa and Australia. Comparing the occurrence frequency on the ocean and that on the land, the irregularity distributed more on the ocean, but the lightning occurred most on the land. However, in terms of lightning radiances, the intense lightning events were usually found in the oceans, which imply the topside ionospheric irregularity is related to the intense lightning distribution. Furthermore, we select two spatially-temporally coincident cases of the TRMM lightning events and the ROCSAT-1 plasma bubbles for detailed analysis. Case I (2001/2/2 18:26~18:33 UT): One minute after TRMM observed a group of lightning events (continued about 2 minutes) a localized structure of ionospheric irregularity was observed by ROCSAT-1 in southeast of the lightning region. From spectral analysis, we found plasma waves with wavelengths of about 20m~1000m. If we convert the ion velocity perturbation into the equivalent electric field perturbation, the magnitude is about 2.5 mV/m, which is comparable to that of the lightning induced electro-magnetic pulse transmitted to the 200km altitude. Hodograph analysis indicates that the polarization of 50m~120m waves is right-hand elliptically polarized. Case II (2001/1/26 00:36~00:51 UT): during this orbit ROCSAT-1 observed density depletions without vertical drift perturbation before the lightning events. However, after the lightning both small scale density depletions and the velocity fluctuations were observed. The spectral characteristics of these structures display wave dispersion indicating that shorter waves go faster than that of longer waves after the lightning. From the statistical or case studies, we tend to conclude that the strong lightning induced electro-magnetic waves can affect the density and velocity structures locally in the topside ionosphere, but not the main factors to trigger the occurrence of large-scale irregularities in the F-region.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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