| 摘要: | 本論文研究主題，在於瞭解低層大氣和中高層大氣間的耦合機制，尤其專注於低層大氣的雷暴系統。因其對應中高層大氣的影響，除了透過「力學波」的能量沉積外，也可能伴隨電磁耦合機制。除此之外，雷暴內的閃電活動，亦可能造成中層大氣的放電現象，因而產生紅色精靈。
我們研究了2014年4月28日孟加拉雷暴內，罕見的紅色精靈、閃電及大氣重力波變化現象，深入探討雷暴所引發重力波、及低層大氣與中高層大氣間的「電耦合」過程。由雷暴產生重力波、雷電與紅色精靈間的詳細關係，科學文獻迄今鮮少詳細述及。透過對此非比尋常事件—當日所拍攝喜馬拉雅山區上空影像、閃電資料及氣象衛星雲圖的分析後，大大提升我們對雷暴產生重力波、閃電和紅色精靈發展歷程的理解。
重力波是大氣中最基本的動力過程，要瞭解大氣重力波，必先求解其特徵參數。因為大氣重力波從低層大氣到中高層大氣的傳播過程，可能調制輻射強度，尤其會對OH和OI557.7氣輝層產生擾動。「全天空成像儀」是科學界觀察氣輝擾動的重要工具，然而，2014年4月28日此紅色精靈、閃電和重力波同現的不尋常偶發事件，且恰巧被業餘攝影師以數位相機所記錄，但此影像欠缺精確方位角、高度角和亮度的量測值。故利用不同於傳統處理「全天空影像儀」資料的方式，以嶄新方法分析重力波的特徵參數。
我們發展分析氣輝影像的新技術包含：(1)對於幾何校正，利用影像背景恒星的精確位置，以校準觀測重力波。(2)對於亮度校正，利用已考慮大氣吸收率的恒星視星等，作為重力波調制氣輝強度的參考。(3)對於重力波波長，運用「Lomb-Scargle」分析重力波影像的功率頻譜。經過比較前人對「重力波參數獲取」研究結論，顯示分析方法合宜。為提高「原拍攝氣輝影像」的幾何及輻射精度，我們發展前述的新分析技術。對於後續以低成本、便攜性的高機動「全天空影像儀」觀測台灣的預期規劃，應該是確切可行的。
;The main focus of this thesis is to reveal the severe impact of the lower atmosphere on the middle/upper atmosphere environment. Especially for the thunderstorm system in the lower atmosphere, the caused effects of middle/upper atmosphere not only includes the energy deposition of the mechanical wave but also involves the electromagnetic coupling process. Lightning activity in a thunderstorm may cause the middle atmospheric discharge phenomena associated with the occurrence of sprites.
In this thesis, we studied an unusual event with sprites, lighting activity and gravity wave which is generated by a storm over Bangladesh on Apr 28, 2014, and investigated the thunderstorm-generated gravity wave and the electric-coupling process between the lower atmosphere and the middle/upper atmosphere.
To date, the detailed relationships among gravity waves, lightning, and sprites generated by the thunderstorm have rarely been documented in the scientific literature. For the unusual event over the Himalayan region on Apr 28, 2014, after analyzing the recorded sprites images, lightning data and weather satellite map, we improve our understanding of the whole process of thunderstorm produced gravity waves, lightning and sprites and their sequences.
The gravity wave (GW) is one of the fundamental dynamic processes in the atmosphere. The first step to understand the GW dynamics is to estimate the salient parameters of gravity waves since the propagation of atmospheric gravity waves from lower to middle/upper atmosphere may result in the modulation of emission intensities, especially for disturbance of OH and OI (557.7 nm) airglow layer.
All-Sky Imager is one of the important tools to observe the airglow modulation in the scientific community. However, an unusual event (Apr 28, 2014) with sprites, lighting activity, and gravity wave was recorded by an amateur photographer with a digital camera. The precise measurements of azimuthal/elevation angle and brightness were lacked.
The required analysis technique for precisely quantizing the GW parameters are different from the traditional method adopted in All-Sky Imager data. For geometry calibration, we utilized the precise location of the background stars to retrieve the geometry of the observed gravity waves. For brightness calibration, the apparent magnitude of recorded stars with considering atmosphere absorption are referenced to the modulated airglow intensity of GW. For wavelength length and GW period, we analyzed GW images with the Lomb-Scargle power spectrum. Our adopted analyses are validated through comparison of the obtained parameters of the gravity waves with the reports in the previous studies.
We developed the analyzing techniques for the recorded airglow images with improving the accuracy of geometry and intensity. The developed method is practical and useful especially for a low-cost, portable and highly mobile for All-Sky Imager observation in Taiwan. |
