Isual Publications 2014

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2015 21 周容光,雷暴系統的向上放電現象,博士論文,國立成功大學物理研究所,2015

雷暴系統的向上放電現象在近二十年才被記錄到影像,因為他們的外形類似噴泉的圓錐體所以被命名為噴流事件。噴流事件被歸類在高空短暫發光現象,其為介於雷暴系統頂部至電離層底部的大尺度發光現象。依據放電抵達的高度噴流事件主要分成blue starter、藍色噴流以及巨大噴流。自從2004年5月福爾摩沙衛星二號升空後,其科學酬載“高空大氣閃電影像儀(Imager of Sprites and Upper Atmospheric Lightning, ISUAL)”持續地進行全球性的高空短暫發光現象觀測。至2015年6月30日,ISUAL紀錄了接近100個巨大噴流,其被認定建立了直接連接雷暴系統頂部至電離層底部的通道。除了典型帶負電荷往上放電的巨大噴流之外,另外還有兩種類型的巨大噴流。第一類型巨大噴流的動態發展類似於地面觀測到的帶負電荷往上放電的巨大噴流。由電磁波訊號,第一類型巨大噴流認定為帶負電荷從雲頂至電離層的放電。第二類型巨大噴流的動態發展一開始為藍色噴流再慢慢往上形成巨大噴流,被猜測為介於雷暴系統上層正電荷層與負電荷屏蔽層之間所觸發的藍色噴流類型之放電。光度的特性指出第二類型巨大噴流是由正流束所組成,更進一步的天電訊號分析顯示一個ISUAL所紀錄的第二類型巨大噴流為帶正電荷往上的放電。第三類型巨大噴流則是在閃電發生之後靠近閃電的位置附近所發展的巨大噴流,其放電極性猜測與觸發閃電所造成的電荷不平衡有關。 
2007年7月22日由地面觀測拍攝到38個發生於雷暴系統之上的噴流事件,其中一個事件為第二類型巨大噴流,此為第一個由地面觀測所記錄到的第二類型巨大噴流。由裝載不同濾鏡的攝影機所記錄的影像,噴流事件被發現有清楚的紅光,而他們的藍光幾乎被大氣散射所以在影像中無法分辨。由理論估計流束的發光,結果顯示在blue starter以及藍色噴流上方區域的紅光主要來自氮氣第一正則譜系。因為在噴流事件發生之期間,相同雷暴系統所產生的閃電之天電訊號沒有被記錄到,噴流事件與閃電活動的關聯性則由影像中雲內閃電或是對地閃電所造成雲的發光來分析。分析結果顯示兩者的關聯性相當複雜,有些噴流事件的出現會受先前發生在當地的對地閃電或者鄰近的雲內或對地閃電影響,而有些噴流事件的出現則可能影響後續發生的閃電活動。 
ISUAL紀錄了許多神秘的藍色發光事件,它們輻射明顯的中紫外光至藍光(230−450 nm)以及暗淡的紅光(653−754 nm)。大多數的藍色發光事件在ISUAL所紀錄的影像中呈現小亮點狀,一小部分的事件則往上且緩慢地發展,最終成為藍色噴流或者第二類型巨大噴流。對應於藍色發光事件的極低頻至甚低頻波段以及低頻波段的天電訊號,其波形與甚低頻至低頻波段的雙極窄脈衝事件之波形相似,推測ISUAL的藍色發光事件應是與雙極窄脈衝事件類似的事件所伴隨的發光。藍色發光事件中有對應正與反二種極性的放電;由天電訊號與ISUAL光學資料,藍色發光事件與雷暴系統中初始放電的快速電流有關,而藍色噴流或第二型巨大噴流,則推測與後續緩慢地變化的放電電流有關。藍色發光事件的光譜特性顯示發光主要來自由局域增強的電場所產生之非熱平衡大氣電漿,而非來自局域熱力平衡的高溫大氣電漿。

The upward discharges from the electrified thunderstorms have only been recorded about two decades ago. They are termed as jets because of their fountain-like cone shapes. Jets are members of the transient luminous events (TLEs) which are large-scale transient optical phenomena occurring between the top of the thunderstorms and the lower ionosphere. Characterized by their terminating altitudes, the prominent family of jets includes blue starters, blue jets (BJs), and gigantic jets (GJs). The ISUAL (Imager of Sprites and Upper Atmospheric Lightning) experiment on the FORMOSAT-2 satellite has continuously and globally surveyed TLEs from space since it was launched in May 2004. As of 30 June 2015, ISUAL has recorded nearly a hundred gigantic jets, which are believed to establish a direct discharge channel between the thunderstorm top and the lower ionosphere. Besides the known class of negative GJs, which are called type I, the data reveal that there are two additional kinds of gigantic jets. The dynamic evolution of the type I GJs resembles that of the negative GJs observed from the ground. Based on the electromagnetic data, type I GJs are identified as negative cloud‐to‐ionosphere‐discharge events (−CIs). The dynamic evolution of a type II GJ starts as a blue jet then slowly develops into a GJ. The type II GJs are conjectured to be blue-jet-type discharges that initiate between the upper positive charge layer and the negative screen charge layer in a thunderstorm. Photometric features indicate that type II GJs are composed of positive streamers. A further analysis of the associated atmospherics (also called sferics) of one ISUAL recorded type II GJ indicates that this GJ is a positive upward discharge. Type III GJs were preceded by lightning, and a GJ subsequently occurred near this preceding lightning. The discharge polarity of the type III GJs is expected to vary and depends on the charge imbalance left behind by the trigger lighting. 
On 22 July 2007, thirty-eight jets occurring over a thunderstorm were recorded during a ground campaign. One of them is a type II GJ, which was the first GJ of this type that was recorded from the ground. Based on the images recorded by a cluster of filter‐equipped cameras, the jets are found to have significant red emissions. However, the blue emissions from these jets were not discernible due to severe atmospheric scattering. A modeling estimation of the emissions from a streamer reveals that the red emissions originated in the upper parts of blue starters and blue jets would be mainly from the first positive system of N2 (1PN2). Since no lightning‐associated sferics from this thunderstorm during the jet‐generating period were found, correlation patterns between the jets and the lightning activity are analyzed from the illumination of clouds due to intra-cloud (ICs) and cloud-to-ground (CGs) lightning. The correlation patterns exhibit considerable complexity but also indicate that the occurrence of jets can be affected by the preceding local CG lightning or nearby lightning (IC or CG), while in turn the jets might also influence the ensuing lightning activity. 
ISUAL has recorded many mystic blue luminous events (BLEs) that emit clear middle ultraviolet to blue emissions (230−450 nm) but contain dim red emissions (653−754 nm). Most BLEs appear to be dot-like on the ISUAL images, and a few BLEs develop upwardly and slowly into blue jets or type II GJs. The associated sferics of the BLEs in the extremely low frequency to the very low frequency (ELF/VLF) band and the low frequency (LF) band exhibit similar features to those of the VLF/LF waveform for the narrow bipolar events (NBEs). The ISUAL BLE is conjectured to be the accompanied light emissions of the NBE-like event. Both positive and negative discharge polarity-types for the BLEs have been found. Based on the sferics data and the ISUAL optical data, a NBE-like event is found to be related to a rapidly-flowing current of the initiation discharge in the thunderstorm, while a blue jet or a type II GJ is suggested to be associated with the slowly-varying current of the ensuing discharge. The spectral characteristics of BLEs resemble those of the emissions mostly from the non-thermal air plasmas produced by the locally-enhanced electric field, rather than those from the hot air plasmas in local thermodynamic equilibrium (LTE).

2015 22 張淑鈞,與Elves關聯的光學與電波輻射及其應用,博士論文,國立成功大學物理研究所,2015

        過去國內外的地面觀測結果顯示Sprite(紅色精靈)是發生率最高的高空短暫發光現象(Transient Luminous Events; TLEs),然而從ISUAL開始進行觀測之後,發現全球分佈以elves(淘氣精靈)發生率最高。elves的型態為甜甜圈狀與盤狀,與閃電發生有密切關係,因此elves被認為是由閃電所輻射的電磁波所引發的。由於elve和閃電幾乎同時發生,因此觀測上,除了閃電發生在地平線後的事件之外,elves的光學影像及光度常常受到閃電的汙染。然而ISUAL為臨邊觀測(limb viewing),因此可紀錄閃電在地平線後的elves事件。先前關於ISUAL elve的研究指出,elve的發光主要來自被激發的氮氣分子(N2),包含N2 Lyman-Birge Hopfield(N2 LBH)和N2 first positive(N21P)等波段,且N2 1P的亮度和閃電峰值電流有關。 
        在ISUAL 記錄的閃電事件中,有一些具有遠紫外光(Far Ultraviolet; FUV)訊號,但是沒有伴隨的TLEs,我們猜測這些遠紫外光訊號可能來自於閃電或是影像中看不見的TLE,稱為“mystic FUV events”。經由計算閃電可能的遠紫外光輻射強度以及考慮大氣吸收後,已排除閃電的可能性;而由ISUAL的光譜光度資料訊號,發現mystic FUV events其遠紫外光訊號與閃電訊號峰值的時間間隔相差小於1 毫秒,與elves特性相似,分析elves在影像中的亮度以及FUV的強度後,發現兩者間呈線性關係,因此從elves的FUV強度也可對應到閃電峰值電流強度(SP1-Ip)。除此之外,mystic FUV events其SP1強度大約分布在104 photon/cm2以下,然而elves的SP1訊號強度可達6×104 photon/cm2,因此我們認為mystic FUV events是強度較弱的淘氣精靈所貢獻的。 
        從2009年開始,超低頻(ULF)和甚低頻(VLF)無線電波偵測站陸續被建構,2010年8月之後,兩個測站同步紀錄資料並提供穩定的資料。我們進一步比對ISUAL在2011到2012年所紀錄距離臺灣1500公里的elves事件,藉由分析相對應的閃電電波(sferics)訊號強度,可獲得sferics傳播時的衰減率。結果顯示,VLF磁場訊號強度對距離的衰減率為-1.207 ,而ULF訊號強度對距離的衰減率為-0.871。 
        除此之外,2010年8月時,地面光學觀測系統紀錄到72個高空短暫發光現象,除了光學影像,閃電的電波訊號也有被ULF和VLF測站紀錄到。將ULF 和VLF訊號強度歸一至500公里處的強度時,發現對應不同TLE的閃電,他們的ULF和VLF訊號強度的比例不同。其中Halo-producing lightning的ULF/VLF ratio為elve-producing lightning的三倍左右,然而雖然halo-producing lightning的ULF/VLF ratio和halo-sprite-producing lightning相近,但是halo-sprite lightning的ULF訊號較強。因此,我們可以從ULF/VLF peak ratio或是ULF和VLF的強度來辨別TLEs。除此之外,比較觀測和模擬的ULF和VLF訊號強度比例,發現halo-producing lightning的放電時間(dtstroke)大於300 μs ,而elve-producing lightning的放電時間在100-200 μs。 
        藉由分析ISUAL 2011-2012地平線後的elve事件,發現SP1-Ip大於~150 kA有相對應的氮氣離子(N2+1N(0,0))光學訊號,也就是有因為游離而產生的電子濃度增加現象。在這些事件中,其中SP1-Ip最強的是~300 kA,藉由elve model估計最大可使電子濃度增加~250%。在這樣的環境下,若後續閃電強度與前一個相同,所產生的elve其上半部亮度減少,下半部亮度增加。除此之外,比對ISUAL elve事件和量測到的日本JJI VLF訊號擾動,發現SP1-Ip大於~150kA的elve事件有相對應的振幅擾動,因此VLF電波訊號對於局部的電子濃度變化較為敏感。

Before ISUAL (Imager of Sprite and Upper Atmospheric Lightning) starts to carry out routine space-borne observations, sprite is often noted to be the most frequently observed species of TLEs (Transient Luminous Events). Since then, the ISUAL global survey data unequivocally demonstrate that elves actually are the most abundant species of TLEs. It has been proposed that the mechanism which generates elves is the electromagnetic pulse launched by intense lightning, due to their apparent donut shapes. The proximity between elves and the causative lightning renders the spectrophotometer observations of the elve optical emissions are always contaminated by the lightning emissions except for the event triggered by lightning located behind the Earth limb. For this type of behind the limb events, the parent lightning emissions are blocked by the solid earth and thus do not contribute to the data recorded by the ISUAL sensors. Previous studies had also shown the existence of the FUV (N2 LBH) emissions in elves as well as the existence of a tight correlation between the elve N2 1P emission intensity and the lightning peak current. 
        Among the ISUAL recorded elves, there is a special subset of events that contains no discernible transient luminous events (TLEs) in the imager frames except for the bright lightning; however, they do possess a significant associated far ultraviolet (FUV) signal. These events are termed as the “mystic FUV events” or simply the FUV events. After factoring in the atmospheric attenuation, the lightning FUV emission was found to be completely absorbed by the atmosphere hence was extremely unlikely to be detected by the ISUAL sensors at an altitude of 891 km. The FUV emission of the FUV events closely follows the lightning OI emission within 1 ms, similar to the optical characteristics of a typical elve. By analyzing the imager-N2 1P brightness of the elves and their FUV intensity, a linear correlation was found. Thus, the FUV emission intensity of elves can be used to infer the lightning peak current. The intensity of FUV events also ranks among the dimmest elves and is less than 104 photon/cm2. Combining all the information, the FUV events finally are identified as dim elves that eluded the detection of the ISUAL imager. 
        Since 2009, the NCKU team has constructed and continuously operated a ultra-low-frequency (ULF) and a very-low-frequency (VLF) radio band recording stations, to assist the operation of the ISUAL experiment. After the late August of 2010, both stations start to run simultaneously and provide good data. Through analyzing the sferics associated with ISUAL elves that occurred within 1500 km of Taiwan during 2011 and 2012, the attenuations of ULF and VLF sferics in the Earth cavity are obtained. Amplitudes of the ULF and the VLF sferics are found to vary as D-0.871 and D-1.207, respectively; where D is the source distance from the sferic stations. 
        While observing from the southern tip of Taiwan on 2 August 2010, a thunderstorm near Luzon Island-Philippines about 500 km away was found to produce 72 transient luminous events. Besides optical images, ULF and VLF sferics of lightning from this thunderstorm were also recorded. After normalizing the sferics from the 2 August 2010 storm to a 500 km distance source, the ratio of the peak ULF and the VLF magnetic fields is found to be distinct for different types of TLE-producing lightning. The ratio for the halo-producing lightning is nearly three times that of the elve-producing lightning, but it is comparable to that of the halo-sprite-producing lightning; although the ULF strength for the halo-sprite lightning is significantly larger than that for the halo lightning. Therefore, it is possible to distinguish between the TLE-types using the ULF to VLF peak ratio or the strength of ULF/VLF band emissions of the parent lightning. Through comparing the simulated and the observed lightning radiation fields, the best fit for the lightning discharge time (dt_stroke) was found to be larger than 300 μs for the halo-producing lightning. For elve-producing lightning, the inferred lightning discharge time is about 100-200 μs. 
        From analyzing the behind-the-limb elves that were recorded by ISAUL during 2011-2012, the elves generated by lightning with a SP1-inferred peak current (SP1-Ip) greater than ~150 kA are found to be associated with detectable N2+1N(0,0) emissions, which are also referred as the electron density enhancement. In this dataset, the most intense elve was generated by lightning with ~300 kA. Such a lightning will cause a maximum electron density enhancement of ~250 %. Under the assumption that the local electron density can be enhanced by the preceding elve, the N2 1P and N2 LBH photon emission of follow-up elve which generated by the same lightning show a significant decrease in the brightness for the upper part and a significant increase for the lower part in comparison with the preceding elve. Also, through analyzing the ISUAL elve and the amplitude of the Japan JJI VLF transmitter signals, elve generated by lightning with a peak current greater than ~150 kA is found to produce an amplitude change in the transmitter’s VLF signals. We demonstrate that the VLF signals is sensitive to the local electron density changes that they transverse. Therefore, the changes in the VLF signals from transmitters can be used to infer the electron density enhancement due to elves or other types of TLEs. 

2015 23 黃柏勛,使用希爾伯特黃方法分析高空短暫發光現象的早期訊號,碩士論文,國立成功大學物理研究所,2015
2015 24 曹祖維,適用於皮米衛星任務之微小化太陽極紫外線光度計,碩士論文,國立成功大學太空與電漿科學研究所,2015

成功大學團隊研製2-U立方衛星PHOENIX參與歐盟之QB50任務。PHOENIX在搭載滿足任務需求之酬載: 離子與中性粒子質譜儀、熱敏電阻外,尚有餘裕可容納其它酬載。基於極紫外線對於反應太陽活動和增溫層環境顯著的影響,本論文逐發展一科學酬載: 太陽極紫外線感測器。紫外線輻射屬於波長低於400 nm的波段,在太陽輻射中的變動較可見光大得多,並與太陽活動高度相關。地球大氣層會完全吸收該波段,其中少量極紫外線通量的變化就會造成大氣變動。雖然極紫外線只占太陽輻射總量的1%,這些輻射扮演了加熱上層大氣、光分解與游離現象的主要角色。過去對紫外線輻射量測的儀器大多體積龐大且需要高壓電,我們欲發展微小化且低耗能的太陽極紫外線感測器,使其容易滿足中小型載具的任務需求,爭取更多執行任務的機會。本感測器的原理是光電效應,藉由陽光照射在電極上產生之光電流來量測極紫外線。由於PHOENIX將於電漿層內執行任務,為了驅散自由電子而在電極上所施加的負向偏壓,會在電漿環境中吸引帶正電的離子,形成電漿電流。所以我們把功函數不同的兩種金屬電極做為一組,安裝兩組在衛星的不同方位上做量測,將能經過計算來消去電漿電流的影響。我們已對太陽極紫外線感測器在有或無電漿的環境下、光源與電極不同的距離與角度下,進行紫外線照射的實驗。在實驗中,本感測器能夠精確量測到微小變化的電漿電流,會因為電極功函數的差異而量測到不同的光電流。對於紫外線光源不同的距離與角度也有相應的回饋。因為具有低重量、低耗電與小體積的特點,本項設計可以滿足皮米衛星的實驗需求,也能使用於探空火箭與氣球任務上。

The PHOENIX satellite is a 2-U CubeSat that has been developed at National Cheng Kung University (NCKU) as a unit of the QB50 mission, which is an international space collaboration coordinated by the von Karman Institute. One of the main objectives of the QB50 mission is to carry out the in-situ measurements at the lower thermosphere which is rarely explored in traditional satellite missions. The PHOENIX CubeSat is to fulfill the above goal by accommodating following payloads: an Ion and Neutral Mass Spectrometer, Thermistors, and a Solar Extreme Ultraviolet Probe (SEUV Probe) which was developed in this study. The solar extreme ultraviolet (EUV) radiation is the main energy source in the thermosphere. Accurate knowledge of this radiation is of prime importance for space weather, satellite drag, telecommunication and positioning. The photoelectric current from 4 planar copper-based electrodes plated with gold and tin are produced by energetic EUV photons. The electrodes with different metal plating can be used to eliminate the current contributed by the environmental space plasma. Two sets of electrodes (a gold one and a tin one each set) are located on different orientations of the PHOENIX CubeSat, thus the photoelectric current caused by the different normal components on the electrode surface can help to determine the inclination angle of the Sun. Therefore the SEUV Probe can also act as an auxiliary device of the sun sensor and Attitude Determination and Control System. The functional and scientific performance tests of the SEUV probe have been done in the plasma chamber and reported in this thesis. With the feature of low power consumption, compact and lightweight, SEUV probe can satisfy the requirements of not only the QB50 but also further CubeSat missions, and can be utilized in sounding balloon and rocket experiments.

2015 25 莊承翰,閃電電場模擬與人工觸發閃電的可行性研究,碩士論文,國立成功大學太空與電漿科學研究所,2015
2015 26 溫少群,平流層以下之大氣電場量測,碩士論文,國立成功大學物理研究所,2015
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Wednesday the 17th. ISUAL. All rights reserved.