Relativistic Runaway Discharges in the Earth's Atmosphere

该提案旨在提高人们对地球大气中与闪电活动有关的壮观自然现象的认识。其中一些过程被社区称为精灵，蓝色和巨大的喷气机等。这些都引起了全球一些公民科学家的注意。其中一种尚未被完全理解的现象被称为陆地伽玛射线闪光或TGFs。在这些事件中，会产生高能的x射线爆发。这项研究的主要目标是发展理论工作，以阐明tgf的来源。这项跨学科的工作结合了等离子体物理和大气过程的概念。这可能与开发新的x射线源有关，可能对医学成像过程产生影响。建议的工作将导致研究生的培训，并将成为博士论文的一部分。提出这项工作的主要动机来自最近对TGF的一些观察，并探索导致这些事件的潜在物理过程。导致电子雪崩倍增的核心物理过程是由电场施加的力加速。在地球物理背景下，该场是由雷云电气化产生的环境场或由雷暴引线产生的。这些电子从电场中获得能量，并在电离碰撞中快速倍增。在相对论中，当这些电子被空气中的氮和氧原子的原子核散射时，它们可以辐射出高能光子（x射线）。这种辐射被称为制动辐射或轫致辐射。这些x射线向各个方向辐射，有一部分随着电子运动而向后辐射。由于光电效应，这些x射线可以产生种子电子，从而导致原始雪崩的强烈放大。这个过程被称为反馈过程。最近发现，这些效应发生在非常小的空间尺度上，与现有的观测结果很好地吻合。这个项目研究导致观察到的现象的确切物理机制。通过对学生的指导，教育和知识转移将受益于拟议的活动。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The proposal aims at advancing the knowledge of spectacular naturally occurring phenomena related to lightning activity in the Earth’s atmosphere. Several of such processes are known to the community as sprites, blue and gigantic jets etc. These have attracted the attention of several citizen scientists all over the globe. One such phenomenon, which is still not completely understood is referred to as terrestrial gamma-ray flashes or TGFs. During these events, bursts of X-rays with high energy are generated. The main goal of this research is to develop theoretical work that will shed light on the sources of TGFs. This inter-disciplinary work combines concepts of plasma physics as well as atmospheric processes. It may be relevant to the development of new X-ray sources with possible implications on medical imaging processes. The proposed work will result in the training of a graduate student and will be part of the doctorate thesis. The main motivation for the proposed work results from some recent observations of TGF’s and exploring the underlying physical processes responsible for these events. The core physical process leading is avalanche multiplication of electrons accelerated by force exerted by electric field. In geophysical context the field is generated either as ambient field due to thundercloud electrification or produced by lightning leaders. These electrons gain energy from the electric field and experience quick multiplication in ionizing collisions. In relativistic regime these electrons can radiate energetic photons (X-rays) as they scatter by nuclei of nitrogen and oxygen atoms in air. The radiation is referred to as braking or bremsstrahlung radiation. These X-rays are radiated in all directions and some fraction is radiated backwards with respect to electron motion. These X-rays can produce seed electrons due to photoelectric effect and this leads to strong amplification of the original avalanche. This process is referred to as feedback process. It was discovered recently that these effects occur on very small spatial scales in good agreement with existing observations. This project investigates the exact physical regimes which lead to observed phenomena. The education and transfer of knowledge will benefit from the proposed activity through the mentoring of students.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.