Three-Dimensional Numerical Modeling of Sprite Streamers

该奖项将使用最近开发的高性能等离子体放电流体模拟程序，结合最新的精灵高速图像，研究精灵流光的基本物理。大约30年前，人们发现强烈的闪电可以在地球上层大气中引起壮观的瞬变发光事件(TLE)。精灵是TLE的一种。随后的研究发现，精灵的物理特征与通常所知的地面附近的火花放电相似。然而，它们的体积要大得多，寿命也更长，因为它们发生在空气密度大大降低的环境中。精灵可以对高层大气的物理和化学性质造成重大改变，能够影响某些无线电频段的传播，以便进行远程通信。高分辨率的精灵图像显示，它们由大量的被称为流光的等离子细丝组成。人们已经认识到，理解流光物理是学习精灵动力学和效果的关键。该项目将利用一种先进的计算机模拟工具来研究各种鲜为人知的拖缆过程。它将极大地促进我们对精灵的物理和效应的理解。这项研究将增进对介质击穿和瞬变等离子体放电的认识，并提高闪电预报和安全性。在这个项目中开发的软件将是开源的。研究生和本科生将得到支持并参与这一研究项目，从而为STEM劳动力发展做出贡献。该项目将研究流光分支、流光头之间的碰撞、流光头与流光通道之间的碰撞、中性密度扰动对流光动力学的影响，以及流光与低电离层之间的相互作用。各种三维模拟将使用最近开发的高性能等离子体放电流体程序Amplifi(等离子体起始、细丝和相互作用的自适应建模)来执行，以了解这些过程的物理过程，它们在精灵动力学中的作用，它们的电和光学效应，以及它们对周围环境的依赖。该项目还将为解释精灵的高速图像和理解其含义提供关键信息。将获得关于精灵流光动力学对环境中性或电气条件的依赖的具体知识，这将使开发潜在强大的遥感方法，通过观测精灵来研究中间层/D区域电离层。中性密度扰动对精灵流光动力学影响的研究还将揭示一种由强电场实现的新的中性离子耦合机制。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award will investigate the fundamental physics of sprite streamers using a recently developed, high-performance plasma discharge fluid simulation code, in close conjunction with the latest high-speed images of sprites. About thirty years ago, it was discovered that powerful lightning strokes can cause spectacular Transient Luminous Events (TLEs) in the earth’s upper atmosphere. Sprites are one of the TLEs. Subsequent research has found that sprites share similar physical characteristics as those commonly known spark discharges near the ground. They, however, are much larger and last much longer, because they occur in an environment with greatly reduced air density. Sprites can cause significant modifications of the physical and chemical properties of the upper atmosphere, capable of affecting the propagation of certain radio frequency bands for long-range communications. High-resolution images of sprites have revealed that they consist of a large number of plasma filaments known as streamers. It has been recognized that understanding streamer physics holds the key to learning sprite dynamics and effects. This project will utilize an advanced computer simulation tool to study various poorly understood streamer processes. It will greatly advance our understanding of the physics and effects of sprites. The study will advance knowledge of dielectric breakdown and transient plasma discharges and improve lightning forecast and safety. The software developed in this project will be open source. Graduate and undergraduate students will be supported and involved in this research project, thus contributing to STEM workforce development. This project will investigate streamer branching, collisions between streamer heads, collisions between streamer heads and streamer channels, effects of neutral density perturbations on streamer dynamics, and interaction between streamers and the lower ionosphere. Various three-dimensional simulations will be performed using a high-performance plasma discharge fluid code called AMPLIFI (Adaptive Modeling of PLasma Initiation, Filamentation and Interaction), which was recently developed, to understand the physics of these processes, their roles in sprite dynamics, their electrical and optical effects, and their dependence on the ambient environment. This project will also provide critical information for interpreting high-speed images of sprites and understanding the implications. Concrete knowledge of the dependence of sprite streamer dynamics on ambient neutral or electrical conditions will be obtained, and this will enable the development of potentially powerful remote sensing approaches to studying the mesosphere/D region ionosphere by observing sprites. The study of the neutral density perturbation effects on sprite streamer dynamics will also reveal a novel neutral-ion coupling mechanism enabled by a strong electric field.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.