Investigating the relationship between nonthermal electron properties and geoeffective Lyman-alpha emission in solar flares

太阳耀斑是一种强烈的喷发事件，涉及在太阳大气中迅速释放大量储存的能量，促进发射包括X射线和极端紫外线(EUV)在内的多个波长的过剩辐射。中性氢的莱曼-阿尔法线是太阳光谱中最强的发射线，已知它构成了太阳耀斑总辐射能量的相当大一部分。近年来，对莱曼-阿尔法的研究兴趣有所增加，这是因为在耀斑时间尺度上在这个波长上的观测结果有所改善。在静止的太阳条件下，莱曼-阿尔法辐射通过组成元素的电离形成并维持地球电离层的D区，最近的研究表明，在太阳耀斑期间发射的莱曼-阿尔法在E区电流的形成中起着重要作用。对电离层的扰动可能对导航和通信系统产生不利影响，因此了解造成这些影响的辐射对空间气象和大气研究至关重要。此外，在理解过量辐射对地球的影响方面，可以扩展到其他行星大气，有助于迅速发展的寻找宜居系外行星。人们普遍认为，加速的非热电子与色球碰撞是太阳耀斑期间发射过剩辐射的原因。然而，在太阳圆盘上类似位置发生的相同X射线量级的耀斑，可能会显示出显著不同的对应莱曼-阿尔法反应。因此，这项研究的主要目的是研究非热电子的性质如何影响太阳耀斑中相应的莱曼-阿尔法(以及其他EUV线和连续体)发射轮廓。为此，将使用NASA戈达德太空飞行中心的团队开发的定制计算软件对同时从RHESSI、GOES和SDO获得的太阳圆盘上类似位置的太阳耀斑的多波长光谱观测进行分析。这将有助于诊断与耀斑有关的非热电子性质，估计色球中的沉积能量，并与耀斑辐射的莱曼-阿尔法和其他EUV分量的辐射损失进行比较。这些数据还将作为最先进的辐射流体力学和大气模型的观测输入，这将使我们能够调查预测的莱曼-阿尔法发射曲线与天基仪器观测到的数据之间的差异。最终，这项研究将提供更好的理解，了解太阳耀斑中加速电子的基本性质如何决定它们的地球效应水平。这项研究恰逢太阳活动在第25太阳周期开始时增加。在未来，这项研究将指导来自NASA、ESA和JAXA太阳飞行任务上的新一代X射线和Lyman Alpha仪器的未来Lyman-Alpha数据集的解释，并为未来辐射流体动力学和大气模型的发展提供工具。

Solar flares are intense eruptive events that involve the rapid release of large quantities of stored energy in the solar atmosphere, promoting the emission of excess radiation in multiple wavelengths including X-ray and Extreme Ultraviolet (EUV). The Lyman-alpha line of neutral hydrogen is the most intense emission line in the solar spectrum and is known to constitute a considerable portion of the total radiated energy in solar flares. Interest in the study of Lyman-alpha has increased in recent years, due to the improved availability of observations at this wavelength on flare timescales. In quiescent solar conditions, Lyman-alpha radiation is known to form and maintain the D-region of Earth's ionosphere through ionisation of constituent elements and recent studies have suggested that Lyman-alpha emitted during solar flares has a significant role in the formation of currents in the E-region. Perturbations to the ionosphere can have adverse effects on navigation and communication systems, thus understanding the radiation responsible for these effects is crucial to space weather and atmospheric research. Furthermore, in understanding the effects of excess radiation on Earth, extension can be made to other planetary atmospheres, aiding the rapidly developing search for habitable exoplanets.It is generally accepted that accelerated nonthermal electrons colliding with the chromosphere are responsible for the emission of excess radiation during solar flares. However, flares of identical x-ray magnitudes, occurring at similar locations on the solar disk, can show significantly different corresponding Lyman-alpha responses. Thus, the primary objective of this research is to study how the properties of nonthermal electrons influence the corresponding Lyman-alpha (and other EUV line and continua) emission profiles in solar flares. To do this, multi-wavelength spectroscopic observations of solar flares at similar locations on the solar disk taken simultaneously from RHESSI, GOES and SDO will be analysed using bespoke computational software, developed by teams at NASA Goddard Space Flight Centre. This will allow for the diagnosis of flare-related nonthermal electron properties, the estimation of deposited energy in the chromosphere and comparison to the radiative losses in Lyman-alpha and other EUV components of flare radiation. This data will also act as observational input for state-of-the-art radiative-hydrodynamic and atmospheric models, which will allow investigation into the discrepancies between predicted Lyman-alpha emission profiles and those observed by space-based instruments. Ultimately, this research will provide a better understanding of how fundamental properties of accelerated electrons in solar flares can dictate their levels of geoeffectiveness.This research coincides with a rise in solar activity as Solar Cycle 25 commences. In future, this research will guide the interpretation of future Lyman-alpha data sets from the new generation of X-ray and Lyman alpha instruments on board solar missions from NASA, ESA, and JAXA, as well as provide a tool for future developments to radiative-hydrodynamic and atmospheric models.