CEDAR Postdoc: Modeling Studies of Optical Properties of Sprite Streamers and their Chemical Effects on the Upper Atmosphere

该项目进行了一项模拟和观测研究，以研究精灵流光放电的光学性质及其对高层大气的化学影响。雪碧放电是发生在中层和低热层-电离层(MLTI)区域的四种已知类型的瞬变发光事件之一，它们与潜在雷暴中的闪电活动直接相关。尽管一个典型的精灵事件可能会占据高层大气的很大整体体积，但高空间分辨率的精灵事件图像揭示了许多内部的、尚未完全理解的小尺度特征，包括明亮的电离丝状通道。值得注意的是，在精灵中观察到的丝状结构与大气压下的流光放电现象相同，只是在较高海拔的空气密度降低时才会改变。接近地面压力的拖缆的实际应用包括臭氧生产、污染控制和表面处理。然而，目前关于精灵飘带对高层大气的化学效应的了解非常有限。在雷暴期间闪电的驱动下，精灵是电磁能量从对流层高度向上耦合到中层和低电离层区域的表现之一。特别是，高层大气中的闪电放电提供的静电能被转化为其他形式的能量。其中一些分子获得了足够的能量来激发、离解和电离空气中的中性分子(氮气和氧气)。结果，产生了化学活性物质(例如，原子N和O)，它们可以引发一连串的反应，导致高层大气中几种重要成分的产生(例如，NO)。被激发的中性或电离分子发出光子，随后被光学成像仪器观察到为壮观的精灵放电。精灵的发射是电子能量学和能量转换过程的关键指标，目前关于精灵的知识大多是通过分析精灵的发射数据来获得的。精灵中也发生了强烈的电离，这导致了大气电导率的局部改变。因此，在高层大气的能量收支和化学成分方面，精灵是一个重要组成部分，本项目涉及描述和解释精灵飘带的光学特性及其对高层大气的影响的必要性。具体的科学问题是：(1)精灵流光对高层大气的化学作用是什么？(2)精灵流光产生的光发射的动力学是什么？主要成果将是更好地了解精灵飘带的排放和化学影响，包括短期和长期影响。这项调查将为更好、更完整地分析现有和未来的SPRITE数据(例如，FORMOSAT-2卫星上的ISUAL仪器收集的远紫外线和光学数据)提供理论基础。更广泛的影响包括建模者和实验者之间的合作，以及博士后学者的支持和进一步培训。

This project conducts a modeling and observational study to investigate optical properties of sprite streamer discharges and their chemical effects on the upper atmosphere. Sprite discharges represent one of four known types of transient luminous events occurring in the Mesosphere and Lower Thermosphere-Ionosphere (MLTI) regions, which are directly related to the lightning activity in underlying thunderstorms. Although a typical sprite event may occupy a large overall volume of the upper atmosphere, high spatial resolution imagery of sprite events reveals many internal and not yet fully understood small scale features, including bright filamentary channels of ionization. It is quite remarkable that the filamentary structures observed in sprites are the same phenomenon known as streamer discharges at atmospheric pressure, only scaled by reduced air density at higher altitudes. Practical applications of streamers at near ground pressures include ozone production, pollution control and surface processing. However, present knowledge about the chemical effects of sprite streamers on the upper atmosphere is very limited. Driven by lightning discharges during thunderstorms, sprites are one of the manifestations of the upward coupling of electromagnetic energy from tropospheric altitudes to the mesospheric and lower ionospheric regions. In particular, the electrostatic energy provided by lightning discharges in the upper atmosphere is converted into other forms of energy. Some of them obtain sufficient energies to excite, dissociate and ionize neutral molecules in air (N2 and O2). As a result, chemically active species (e.g., atomic N and O) are generated, and they can initiate a chain of reactions leading to production of several important constituents (e.g., NO) in the upper atmosphere. Excited neutral or ionized molecules radiate photons which are subsequently observed by optical imaging instruments as spectacular sprite discharges. The emissions from sprites are a key indicator of electron energetics and the energy conversion process, and the current knowledge about sprites is mostly obtained by analyzing sprite emission data. Intense ionization occurs in sprites as well, which results in the local modification of atmospheric conductivity. Therefore, sprites are an important component within the context of energy budget and chemical composition of the upper atmosphere, and this project addresses the need to characterize and interpret optical properties of sprite streamers and their effects on the upper atmosphere. The specific scientific questions addressed are: (1) What are the chemical effects of sprite streamers on the upper atmosphere? (2) What is the dynamics of optical emissions produced by sprite streamers? The primary result will be better understanding of emissions and chemical effects of sprite streamers, including short and long term effects. The investigation will provide a theoretical basis for a better and more complete analysis of existing and future sprite data (e.g., far-UV and optical data collected by the ISUAL instrument on the FORMOSAT-2 satellite). The broader impacts include collaborations between modelers and experimentalists and the support and further training of a postdoctoral scholar.