Relativistic Runaway Discharges in the Earth's Atmosphere

该提案旨在增进对与地球大气层中的闪电活动有关的壮观自然现象的了解。其中几个这样的过程被社区所熟知，如精灵、蓝色和巨大的喷气式飞机等。这些过程吸引了全球几位公民科学家的注意。其中一种仍未完全了解的现象被称为地面伽马射线闪光或TGFs。在这些事件期间，会产生高能量的X射线爆发。这项研究的主要目标是发展理论工作，以阐明TGFs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。这可能与新的X射线源的发展有关，并可能对医学成像过程产生影响。拟议的工作将培养一名研究生，并将成为博士论文的一部分。拟议工作的主要动机是最近对转化生长因子的一些观察结果，并探索了导致这些事件的潜在物理过程。导致这种现象的核心物理过程是电子在电场作用下加速的雪崩倍增。在地球物理背景下，该场要么是由于雷云带电而产生的环境场，要么是由闪电先导产生的。这些电子从电场中获得能量，并在电离碰撞中经历快速倍增。在相对论状态下，当这些电子被空气中氮和氧原子的原子核散射时，它们可以辐射高能光子(X射线)。这种辐射被称为制动辐射或韧致辐射。这些X射线向各个方向辐射，其中一部分相对于电子运动向后辐射。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，与现有的观测结果非常一致。这个项目调查导致观察到的现象的确切的物理制度。通过对学生的指导，教育和知识的转移将从拟议的活动中受益。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。

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.