Isual Publications 2014

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2000 1 陳小芳(2000),‘Angel sprites的研究’,國立成功大學物理系(學士論文)

在國科會太空計劃室的支持下,由我的指導教授許瑞榮教授翰蘇漢宗教授於1999年七、八月間代表ISUAL科學團隊參加Sprite99的紅色精靈觀測計劃,在美國基特峰國家天文臺(KPNO)做為期一個月的地面觀測。我們將拍攝到的Sprite99觀測資料,利用影像擷取卡配合影像擷取軟體,將有紅色精靈的發生事件擷取成1秒60張(約16ms per frame)的圖片,再存成圖檔,進而分析這些影像。
在本文裡將介紹高空大氣放電現象的研究歷程及Sprite99的紅色精靈影像資料來源,對這些觀測資料的分析都側重於angel sprite的動態行為,在結果與分析的章節裡便是將我們分析這些影像所得到的幾個主要結果:發現先導亮縣(leading glow)、leading glow與後來發生的main streamer和tendril的相對位置關係、測量了main streamer底端到分叉點的距離與main streamer的比例約0.5~0.6間等等的資料分析內容作一呈現。

2000 2 李宜蓁(2000),‘紅色精靈的形態與動態分析’,國立成功大學地球科學系(學士論文)

在國科會太空計劃室的支持下,由我的指導教授許瑞榮教授和蘇漢宗教授於1999 年七、八月間代表ISUAL 科學團隊參加Sprite99 的紅色精靈觀測計劃,在美國基特峰國家天文台(Kitt Peak National Observatory , KPNO)做為期一個月的地面觀測。我們將拍攝到的觀測影像,利用影像擷取卡配合影像擷取軟體,將有紅色精靈的發生事件擷取成1 秒60 張(約16ms per frame)的圖片,再存成圖檔,進而分析這些影像。

在本文中,我們由99 年觀測所得到的資料,將紅色精靈依其外形特徵,做形態上的分類;並經由動態分析,探討它們的形態變化與時間關係。從這些分析,我們得到以下結果:紅色精靈經常成群出現,單獨出現的機會不多,而且它的形態與大氣游離度有關;而大氣游離度的變化,也和兩個紅色精靈事件間的時間間隔有關。至於具有sprite halo 紅色精靈,當它出現時,下方常會伴隨其它形態的紅色精靈;而且它們與前後相關事件的變化,會比一般的紅色精靈事件要複雜。

2002 3 蕭文珊(2002),‘地球高空大氣發光現象的影像分析’,國立成功大學物理系(學士論文)
2007 4 郭政靈(2007),‘福衛二號科學酬載所觀測到的sprites以及elves的分析’,國立成功大學物理研究所(博士論文)

福衛二號是世界上第一個觀測高空短暫發光現象的酬載衛星。衛星上的科學酬載ISUAL包含了影像儀(Imager)、光譜光度儀(Spectrophotometer)以及陣列式光度儀(Array Photometer)等三套儀器,其主要的任務是從太空觀測高空閃電的全球分佈與高時間解析度的光譜光度資料,用以探索產生高空短暫發光現象在地表之分佈與事件內部的物理狀態。本文是分析ISUAL所記錄的紅色精靈與淘氣精靈等兩種高空短暫發光現象,與理論模型的模擬結果相比較,用以檢驗理論的有效性,進而反演出原生閃電的特性。 

紅色精靈通常出現在雷雨雲上方,是一種伴隨著誘發閃電之後幾毫秒之內,發生在地表上空40到90公里高處的發光現象。在紅色精靈中,紅光部份主要是來自氮氣(N2)的第一正則譜系(1PN2),藍光部份則包含氮氣的第二正則譜系(2PN2)及游離氮氣的第一負則譜系(1NN2+)。我們利用理論模型,計算在不同外加電場下的低度游離氣體內,電子激發氮氣各個譜系的激發率,進而得到光譜光度儀中的337.0 nm(1NN2+)通道與391.4 nm (2PN2)通道所量到的強度比相對於外加折合電場的關係。再和衛星觀測數據所推算的比率擬合,反推出紅色精靈內部的折合電場與電子的平均能量和特徵能量分別為~2-3 Ek (Ek為breakdown field=118.5 Td) , 6.2-9.2 eV和4.5-6.5 eV。比Morrill 等人在2002年利用飛機觀測所得的數值高2-3倍,但是卻符合Streamer理論模型所預測的值 (Pasko et al., 1998; Liu and Pasko, 2004;2005;2006)。 

淘氣精靈是閃電的電磁脈衝激發高度87公里左右(電離層的底部)的氮氣,因而產生的發光現象。在此,因為ISAUL可以觀測高空短暫發光現象的紫外線波段,我們延伸前人所發展的淘氣精靈模型(Inan et al., 1996; Veronis et al., 1999,Barrington-Leigh and Inan, 1999),使之可以涵蓋紫外線到近紅外線波段(185-800 nm)的淘氣精靈光譜;同時在計算激發態密度函數時,除了電子激發效應,氣體分子的自發輻射與碰撞退火(collisional quenching)效應之外,也加入影響較小的cascade項,以期得到較完整且精確的結果。另外,我們也考慮大氣中氧氣(O2)與臭氧(O3)的吸收,以及氣體分子的散射(Rayleigh scattering)對ISUAL觀測資料的影響。理論模擬的結果顯示,我們淘氣精靈模型所預測的光譜儀讀值與ISUAL光譜光度儀的觀測值非常接近。在影像的模擬方面,我們考慮地球的曲面的影響,計算出理論上影像儀所應觀測到的淘氣精靈幾何形態,結果也與觀測相當吻合。陣列式光度儀的模擬結果也與ISUAL的觀測結果相當一致。最後,我們在淘氣精靈模型中,給定不同的閃電瞬間電流,以計算淘氣精靈的光度值,再利用觀測到的淘氣精靈光度,反演出產生淘氣精靈的閃電電流峰值。與美國國家閃電探測網(NLDN)所量測的閃電電流峰值比對後,我們發現其中只有兩個事件有相對應的資料,但是由ISUAL所反演出的閃電電流峰值與NLDN所測的電流峰值,相差在25%以內,驗證了理論模擬的可靠性。利用此一驗證的結果,我們可以使用所觀測的淘氣精靈亮度,反演出所對應的原生閃電的電流峰值。結果顯示,我們所選取的淘氣精靈是較亮的事件,其原生閃電的電流峰值是介於160kA與400kA之間;而可以被ISUAL量測的淘氣精靈,其對應的原生閃電的最低電流峰值約為80kA,也就是ISUAL紀錄的淘氣精靈皆來自於大電流閃電。由於衛星的觀測範圍,幾乎涵蓋全球,因此,我們可利用福衛二號的淘氣精靈觀測,用以探討大電流閃電的全球分布情形。

FORMOSAT-2 is the first satellite mission that features a payload dedicating for the survey of upper atmospheric transient luminous phenomena/events (TLEs). The payload consists of three sensor packages including an intensified CCD imager, a six-channel spectrophotometer and a dual-band array photometer. The main mission goals are to obtain the global distribution and the high time resolution spectral information of TLEs. Through these data, the global occurrence of TLEs and the physical conditions in TLEs can be deduced. This thesis work gives detailed analyses of the ISUAL recorded sprites and elves. Theoretical works based on electromagnetic field-driven weakly ionized gases are carried out to elucidate the generating mechanisms and the salient properties of TLEs. The ISUAL (Imager of sprites and upper atmospheric lightning) observational data are used to validate the theoretical results. Reversely, the theoretical results can couple with the experimental data to deduce the peak current of the elve parent lightning. 
Sprites often appear above active thunderstorms following their parent lightning within a few milliseconds, and their luminous bodies span the region between 40 to 90 km altitudes. The reddish glow in sprites is mostly from the N2 first positive group (1PN2), while the bluish glow in the dendritic region comes from N2 second positive group (2PN2) and N2+ first negative group (1NN2+). We numerically simulate the responses of a weakly ionized gas to an externally applied DC E-field to obtain the excitation rates of 2PN2 and 1NN2+ and the ratio of ISUAL SP2 (337.0 nm from 1NN2+) to SP3 (391.4 nm from 2PN2) intensities as a function of the reduced E-field. By fitting the observed ISUAL and the theoretical SP2/SP3 ratios, average electron energy, characteristic electron energy and reduced E-field strength in sprites are derived. The deduced average electron energy is 6.2-9.2 eV and the reduced E-field is ~2-3 times of Ek (Ek is the breakdown field of 118.5 Td) in sprites are higher than those from ground or aircraft campaigns, which reported an average electron energy of ~2.2 eV and an E-field comparable to the breakdown field in strength. However our results are consistent with the predictions from the theoretical streamer model for sprites (Pasko et al., 1998; Liu and Pasko, 2004;2005;2006). 
Elve is a transient luminous glow induced by the lighting-radiated electromagnetic pulse (EMP) at the lower boundary of the nighttime ionosphere at 87 km altitude. Due to the much reduced absorption of the ultraviolet emissions in the rarified upper atmosphere, ISUAL instruments are able to observe the ultraviolet emissions in elves, and thus cover the elve emissions ranging from 185 nm (Far UV) up to 800 nm (Near IR). Hence we extend the lightning EMP model developed by Barrington-Leigh and Inan (1999) to study the ISUAL recorded elves. Moreover, in computing the density of states for the excitation states, the spontaneous emissions, the collisional quenching effects and the contributions of the minor cascading pathways are accounted for. To take into account the effect of atmospheric attenuation, three major attenuation mechanisms: O2, O3 and molecular Rayleigh scattering are considered. The finite curvature of the Earth's surface is also considered while computing the forms of elves. Excellent agreements are found between the modeled emissions and morphologies and those observed by the ISUAL instruments. To validate the elve EMP model, we look for the associated ground lightning data for the ISUAL elves studied in this thesis. Two associated NLDN CG events were found for the 105 behind-the-limb elves. For these two elves, the difference between the photon fluxes measured by the ISUAL Imager and those computed by the EMP model using the NLDN derived peak currents are found to be less than 25%. Finally, the peak currents of the elve-causing cloud-to-ground lightning are derived based on the modeled and the ISUAL observed photometric intensities. For the behind-the-limb elves studied in this thesis, the inferred peak current of the causative CG was 160-400 kA at β=0.5. The relatively high elves initiation current was due to the high pre-set trigger threshold (corresponding to the elve flux induced by an 80 kA CG) of the ISUAL SP and the long event distances of greater than 3700 km. Therefore, ISUAL can be viewed as a space probe of elves and the elve-producing intense lightning.

2007 5 蔡禮聿(2007),‘高空短暫發光現象與劇烈天氣的關連性’,國立成功大學物理研究所(碩士論文)

在已知的高空短暫發光現象中,淘氣精靈是ISUAL 觀測資料中為數最多的一類,它與閃電的關聯性也一直是重要的研究問題。我們從超過4000 個淘氣精靈中,篩選中300 個可清楚分辦淘氣精靈型態和其原生閃電的事件,得出無洞型淘氣精靈與有洞型淘氣精靈的出現比率為2/3。這個結果和原先預期應該和雲間閃電(IC)與雲對地閃電(CG)的比例(IC/CG=3/1)相當的結果大不相同。在此,我們使用傳導線模型(TL model)分別模擬IC 或CG 誘發淘氣精靈的臨界峰值電流與回擊速度,試圖解釋ISUAL 結果之可能成因。另外,我們也介紹了2006 年開始執行的追電計畫:內容包含觀測儀器的建置與初步觀測結果,並以實際飛行任務所拍攝的影像,與地面測試時所拍攝到的巨大噴流影像,說明改良後的自動化觀測儀器的觀測能力。

Among the known species of upper atmospheric transient luminous events, elve is the most abundant in the ISUAL recorded events. The correlation between elves and their causative cloud-to-ground lightning is an interesting problem needed to be addressed. We selected 300 elves with distinct morphology and parent lightnings from the 4000-plus elves recorded by ISUAL since June 2004. From these elves, the ratio between the pancake-shape and the donut-shape elves is deduced to be two to three. This ratio was unexpected since the known occurrence ratio between the inter-cloud discharges (IC) and the cloud-to ground flashes (CG) is known to be around three to one. To explore the root cause behind this discrepancy, this thesis work carried out numerical simulations to determine the minimal peak currents for ICs and CGs to generate these two distinct types of elves. We 
found that the initiating current for the pancake elves from ICs is substantially higher than that for the donut elves from CGs. In this thesis, we also report our cooperation with the DOTSTAR project. Introduction of JOBS (Jet OBservation System) and initial test images are included. Using the same 
camera system, we have successfully observed gigantic jets on ground. Hence, we have demonstrated the capability of this imaging system and its readiness for the future aircraft campaigns.

2008 6 周容光(2008),‘藍色及巨大噴流等高空短暫發光現象之探討’,國立成功大學物理研究所(碩士論文)

近幾年來,高空短暫發光現象吸引了許多的注意與研究。當中的噴流事件由於被觀測的次數很少,所以對它們的特性與機制尚未清楚。在2007年7月22日,我們於鹿林觀測站意外拍攝到多個噴流事件,由多波段觀測系統拍攝的影像,確定噴流事件除了發出藍光之外,紅光也占重要的比例。由這個結果,可以證實福爾摩沙衛星二號記錄的藍色發光事件即是blue starter以及藍色噴流。 
地面觀測的記錄中,有一組噴流事件的序列:首先發生blue starter,並在100毫秒後,在同一雲頂位置發生藍色噴流,更在50毫秒之後發展成巨大噴流。此現象讓我們認為blue starter和藍色噴流是巨大噴流的前導放電過程,如同產生閃電之前的階梯前導。除此之外,我們利用地面觀測所拍攝的連續影像,分析噴流事件與閃電的關聯性,並在噴流事件的周圍一定範圍內,將發生在事件前、後5秒內的所有光學回擊作成累積分布圖。我們發現分布的趨勢除了Wescott et al.在1996年於Geophysical Research Letters發表的結果外,還有其它不同的趨勢,這顯示出發生噴流事件的因素是多樣化的,我們也解釋不同的分布趨勢相對應的物理機制。 
衛星觀測到的藍色發光事件常在短時間內連續發生,其發生率可高達每2秒產生1個事件。分析光譜後發現blue starter和藍色噴流具有相似的光譜特性,這表示它們的產生機制是相似的。在本文中也整理衛星與地面的觀測資料,發現噴流事件有不同的型態,值得未來更深入的研究與討論。

In recent years, transient luminous events (TLEs) have attracted much attention and been intensively studied. The electric jet events of TLEs have rarely been observed, so their characteristics and mechanisms are not well understood. On July 22, 2007, we accidentally captured many jet events. The images from our multi-wavelength TLE cameras show that the jet events not only have blue emissions but also contain red emissions. As a result, it is a strong evidence that the blue luminous events (BLEs) recorded by FORMASA satelliteⅡ are blue starters and blue jets. 
One of the ground observed jet has this event sequence: Firstly, a blue starter occurred, then after one hundred milliseconds a blue jet occurred from the same cloud top. Finally, it developed into a gigantic jet fifty milliseconds later. We suggest that the blue starter and the blue jet could be the leaders of the gigantic jet and they play the roles of the stepped leader in a cloud-to-ground flash. Furthermore, we use the recorded images to look for the relation between the jet event and the lightning activity. The cumulative distribution of optical strokes which occurred around jet events before and after five seconds has been plot. We found that the trends of the cumulative distribution show substantial deviation from those reported by Wescott et al. [1996]. This finding implies that the generating mechanisms of the jet events are much diversified. We also propose the possible physical mechanisms for different cumulative distribution. 
The BLEs recorded by FORMOSA satelliteⅡ often occur in rapid succession within a few seconds. The occurrence rate can be as high as one event for every two seconds. We analyzed their spectra and found that blue starters and blue jets have similar spectral properties. This means that their generation mechanisms are similar. In this thesis, the data from ground and satellite observations have been carefully analyzed. We found that the characteristics of the electric jet events are multifarious. We hope that our results can be good initialing threads for future studies.

2009 7 李立柔(2009),‘影響高空短暫發光現象的綜觀尺度因素’,國立成功大學物理研究所(碩士論文)

從1989年紀錄到第一個紅色精靈影像至今,約經過了二十年,在全球許多地方都已紀錄到高空短暫發光現象的影像,且已證實高空發光現象不只是特定區域的現象。藉由ISUAL的衛星觀測資料,我們可以了解高空短暫發光現象的全球分佈情形。從2004年7月至2008年8月間,ISUAL共紀錄到一萬多個高空短暫發光現象。由TLEs四季的全球分佈特性,我們發現TLEs的分佈約略可發成兩區,低緯度熱帶地區(25°S~25°N)及中緯度溫帶地區(30°以上)。我們分別探討影響這兩區TLEs分佈的綜觀尺度因素,並比較兩區內TLEs的發光強度差異。 

  低緯度地區TLEs分佈隨著季節變化,在赤道附近南北移動的現象,我們推測可能與間熱帶輻合區(Inter-Tropical Convergence Zone,ITCZ)的季節移動有關。由分佈位置統計約有84%的TLEs發生於ITCZ範圍內,且不同區間的TLEs和ITCZ有相似的振盪特性,因此可以了解在熱帶地區中,ITCZ是影響TLEs分佈的綜觀尺度因素。 

  中緯度地區的TLEs在冬季時大量出現,且有集中在特定區域的趨勢,所以發生於溫帶地區的TLEs又稱為winter TLEs。先由個案討論,接著比較每日溫帶氣旋中心與winter TLEs分佈位置,最後比較winter TLEs發生率及風暴路徑頻率。在由小至大的空間尺度下都可以發現,溫帶地區冬季TLEs的發生,與溫帶氣旋引發的天氣系統有關。 

  分別分析淘氣精靈及紅色精靈的發光強度,比較熱帶地區及溫帶地區的事件發光強度。分析結果指出,熱帶地區由太陽輻射直接提供能量,造成的輻合對流,較容易引發發光強度較大的淘氣精靈及紅色精靈;溫帶冬季地區由兩種不同性質的氣團互相推擠,造成的動力抬昇對流,較不易引發的發光強度大的淘氣精靈及紅色精靈。

It has been 20 years since the recording of the first sprite image in 1989. In the past 20 years, TLEs (transient luminous events) have been observed in many geographic locations around the world and these testify that the occurrence of TLEs is a global phenomenon. In this work, we investigate the global distributions of TLEs through analyzing the ISUAL recorded events. Between July 2004 and August 2008, ISUAL payload on the FORMOSAT-2 satellite has registered over ten thousands TLE events. From the seasonal distributions of ISUAL TLEs, they show two distinct distribution patterns; TLEs over the low-latitude tropical region (25°S~25°N) and those over the mid-latitude winter region (greater than 30°). In this work, the synoptic-scale factors of TLE distributions are studied and the luminous intensity of TLEs in the two regions is compared. 

  In the low-latitude region, the distributions of TLEs exhibit seasonal variation and migrate north and south with respect to the equator. We suggest that the seasonal migration of TLE distributions is related to the movement of the ITCZ (inter-tropical convective zones). From correlating the location of TLEs and the distribution of ITCZ, we found that 84% of low-latitude TLEs occurred over the ITCZ and the migrating characteristics of the TLE distribution closely follows that of the ITCZ. Therefore, in the tropical region, we conclude that ITCZ is a key synoptic factor that controls the occurrence of TLE. 

  In the mid-latitude region, the occurrence of TLEs congregates over some specific regions in the winter season. Therefore the TLEs that occur over the winter region are called the winter TLEs. From the case studies that compare the distributions of daily winter storm center and winter TLEs, we realized that winter TLEs are highly correlated to the winter storm. Moreover, the distribution pattern of the winter TLE occurrence density and the storm-track frequency are offset but shows similar pattern. The location analyses we performed all give indication that the occurrences of winter TLEs are correlated with the weather systems induced by winter storms. 

  We also compare the luminous intensity of TLEs from the tropical and winter regions through analyzing the elve and sprite intensities. For TLE over the tropical regions, the events drew their energy from the convective systems that develop from convergence of the wind and, which in turn extract their energy indirectly from the solar radiation; whereas for the TLEs over the winter regions, cold and warm air masses with different properties collide and then the uplift convective systems are developed and eventually produce the winter TLEs. From our analyses, the convective systems in tropical region induce the high intensity TLEs more easily than in winter region.

2009 8 張淑鈞(2009),‘福衛二號「高空大氣影像儀」酬載所記錄的遠紫外光訊號之分析’,國立成功大學物理研究所(碩士論文)

福爾摩沙衛星二號的科學酬載-高空大氣閃電影像儀(The Imager of Sprites and Upper Atmospheric Lightning, ISUAL)進行高空放電現象的觀測已經超過五年,從影像、光譜以及空間上隨時間的變化等資訊已成功分辨出紅色精靈、淘氣精靈、精靈暈盤、巨大噴流、藍色噴流等事件,但是仍有一部份是目前沒有辦法定義及分類的事件。 
  根據前人的研究以及分析ISUAL資料的結果,已經確定紅色精靈、淘氣精靈和巨大噴流這三種高空放電現象具有遠紫外光訊號,不過有很多是影像中只有閃電,但是光譜儀卻記錄到遠紫外光訊號幾乎與閃電同時發生,在本文稱為「待解的事件」。我們推測這些待解的事件可能為影像中的閃電或是因為亮度較暗而無法在影像中成像的高空短暫發光現象所產生的。不過藉由模擬閃電光譜強度及考慮大氣吸收影像後,排除了閃電的可能性。而高空短暫發光現象中,只有淘氣精靈的遠紫外光訊號幾乎與閃電訊號同時,比較淘氣精靈的影像亮度以及遠紫外光強度後,發現兩者間具有高度線性相關性,且待解事件的遠紫外光強度都較小,因此認為待解事件中的遠紫外光訊號來自影像中隱藏的淘氣精靈。 
  另外,利用遠紫外光訊號統計可能的淘氣精靈數量增加倍率,發現實際觀測增加倍率與儀器偵測極限相符,因此實際上有淘氣精靈發生卻被ISUAL遺漏的數量,可藉由考慮儀器偵測極限或經由修正淘氣精靈的逸失比例來加以補救。

Since FORMOSAT-2 launched in 2004, the scientific payload - ISUAL has recorded a large number of transient luminous events (TLEs). Based on the imager, the spectrophotometer (SP), and the array photometer (AP) data, we successfully categorized the recorded events into sprite, elves, halo, gigantic jet, and blue jet. But there are some events that their origins are not properly understood and therefore cannot be classified. 
From previous studies of the ISUAL data analysis, it was found that sprite, elves and gigantic jet all have FUV (Far-Ultraviolet) emissions. However some events that were classified as lightning from the imager data were found to be accompanied by the SP FUV signals; we call these the “undefined events”. We conjectured that the FUV emission from these undefined events is either from lightning or from dim unseen TLEs. To resolve the source of FUV emission for these undefined events, we simulate the lightning optical spectrum and consider atmospheric absorption; it is found that FUV emission from the lightning channel is completely absorbed by the atmosphere and cannot possibly detect by the ISUAL sensors. The brightness of elves in imager and the FUV emission in SP is surprisingly found to be linearly proportional to each other. Furthermore, the SP FUV emission intensity of undefined events were found to be always lower than that from the elve events. Therefore, we conclude that the FUV emission of the undefined events is from the “dim elves” that having brightness below the detect level of the ISUAL imager. 
Beside the SP FUV signal can be used as an elve indicator, we also found that the correction factor for the unseen elves is similar to the estimation based on the instrument detection limit. Hence, by considering the detection limit or by factoring in the under-counting factors, we can correctly find the elve occurrence rate from the ISUAL observed rate.

2009 9 許長仁(2009),‘BF-4 極低頻天線校正及閃電電荷矩計算’,國立成功大學物理研究所(碩士論文)

為了研究高空短暫發光現象與閃電之間的關係,成大團隊在2003 年於鹿林天文台建置極低頻閃電磁場量測系統,包了兩組高感度BF-4 磁場天線與訊號調節器。這套磁場量測系統包含了因訊號調節器所造成的記錄波形變形失真,及磁場天線未經過精確校正兩大問題,使過去數年所記錄的科學資料無法發揮最大效益。這篇論文針對上述的兩項問題進行分析處理。利用訊號傅立葉轉換,結合實驗量測以建立 
波形重建演算法,解決訊號調節器導致的訊號變形。並且製做出一組長螺線管系統,產生適當均勻磁場,對BF-4 磁場天線進行振幅校正與相位差校正。結合上述兩項修正成果,應用於真實高空短暫發光事件的極低頻磁場訊號上,除了可正確重建磁場訊號波形外,也利用地表與電離層間波導管傳遞的電磁波模式,以一個高空短暫發光現象事件相關的閃電為例,計算其電荷矩與電流矩,並且比較校正前後所得到的閃電電磁參數的差別。

 

To explore the physical connection between transient luminous event and associated 
lighting, a magnetic field measurement system at the band-pass of extremely low frequency 
was established at Lulin Observatory in 2003. This system mainly consists of a 
pair of high-sensitivity BF-4 magnetic field induction sensors and a signal modulator. 
Two problems were already revealed and noted by the previous work of Wang [2004], 
one is the waveform distortion caused by the signal modulator, and another one is the 
un-calibration of magnetic field coils. These problems prevent the data recorded by this
system in the past years to be used confidently in the scientific applications. In this study, 
a mathematic work based on the Fourier theory and related experiments are proposed to reconstruct the distorted waveforms. The validations by various waveforms show this approach is functional at the frequency range of 1-117 Hz. A long solenoid was built to produce a uniform magnetic field to calibrate the amplitude and phase responses of the BF-4 sensors over several decades of frequency. An event of an intense lightning with TLE is applied to derive the charge moment change based on the wave guide model of electromagnetic wave propagation between Earth and ionosphere.

2010 10 吳彥蓉(2010),‘聖嬰現象對高空短暫發光現象(淘氣精靈)與閃電活動之影響’,國立成功大學太空天文與電漿科學研究所(碩士論文)

福衛二號高空大氣閃電影像儀(ISUAL)是全球第一個從太空中觀測高空短暫發光現象的衛星酬載。經過五年觀測已累積足夠的資料進行大氣放電現象的全球分佈時間序列之研究,並且第一次有機會以觀測資料探索大氣放電現象與聖嬰南方震盪之間的關係。為了確保ISUAL觀測資料未受儀器衰減影響,本論文分析了ISUAL光譜光度計的長期衰減變化,確認在資料時間範圍內的事件偵測率不受儀器調整與衰減兩項因素的影響。 

以閃電影像偵測儀(LIS)所觀測的閃電、ISUAL所觀測的閃電與淘氣精靈(Elve)等三種不同閃電能量之大氣放電現象資料為樣本。透過建構不同季節、不同放電資料的事件密度以進行空間與時序分析。結果顯示自2004年6月起五年間全球ISUAL閃電與LIS閃電活動變化趨勢一致,且維持穩定均值,但是淘氣精靈發生率有逐年增加的趨勢。五年任務期間共經歷兩次反聖嬰期以及兩次聖嬰期,以標準化距平對三種大氣放電資料進行太平洋區域聖嬰南方震盪冷、暖時期趨勢探討,我們發現淘氣精靈的變化同時具有代表地球環境的太平洋馬蹄形區域以及閃電活動的大溪地附近區域之特徵。 

分析大氣放電現象與聖嬰南方震盪指數的時間相關性找出之聖嬰南方震盪正負強反應區域,分別為換日線赤道區及大溪地區域。採用與南方震盪指數類似之定義,對不同放電現象之事件發生率進行計算,發現所得到的變化曲線與南方震盪指數、Niño 3.4指標皆有高度時間相關性。顯示閃電、淘氣精靈在太平洋區域的變化確實受到聖嬰南方震盪的影響,並且呈現顯著的關連性。

Imager of Sprite and Upper Atmospheric Lightning (ISUAL) onboard the FORMOSAT-2 satellite is the first space-borne scientific payload dedicated to the long-term survey of the transient luminous events (TLEs). To monitor the performance change of the ISUAL sensors, the instrumental degradation and the effective detection efficiency is carefully investigated by the routine calibration observations. The chronic variation of TLE event rates show no notable trend between the annual cycles; this result implies that the detection efficiency of ISUAL has maintained at a constant level in the first 5 years of operation and no correction to the current statistics is necessary. 

We analyze 3 datasets of atmospheric discharge observations from the space, ISUAL-recorded elve, lightning, and LIS-recorded lightning, covering the average energies from high to low respectively. The ISUAL lightning and the LIS lightning rates show similar trend and remain nearly constant from June 2004 to the present, while the seasonal rates of elve increase gradually. Two El Niño events and two La Niña events have experienced in the past 5 years. A standardized anomaly analysis is adapted to identify the elves and lightning variability in the warm and cold phases of ENSO, which is characterized by the South Oscillation Index. The anomaly elve distributions during these episodes are consistent with the Pacific horseshoe pattern and the ENSO lightning characteristics in the Tahiti region. 

The correlation between the atmospheric discharges and the major indices that scientist commonly use to identify ENSO, such as Southern Oscillation Index and Niño 3.4 Oceanic Niño Index, is discussed. The equatorial dateline and the Tahiti regions are chosen as a comparative areas for the elve and lightning as they response to the ENSO episodes. The tight correlation between the atmospheric discharges and ENSO interannual variability provides the concrete evidence that the electricity activity at upper atmosphere can be directly affected by the variation of the ocean and atmosphere conditions.  

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Thursday the 23rd. ISUAL. All rights reserved.