Spectroscopic Signatures of Solar Flare Onset

太阳是距离我们最近的恒星，随着太空现在牢牢地确立为我们社会环境的一部分，它独特的接近对我们来说有着不可避免的后果。虽然太阳辐射为我们的整个生态系统提供了能源，但我们对辐射控制的变化，例如我们的气候，仍然存在巨大的差距。除了太阳输出的长期变化外，太阳还表现出一个活动周期，其组成部分是释放能量的爆炸性事件。这种爆炸性的能量释放发生在无数的尺度上，从纳米耀斑到巨大的喷发耀斑，伴随着被称为日冕物质抛射的等离子体和磁场的大规模喷发，其影响可以在整个太阳和整个日球层看到。其中最极端的事件构成了太阳系内爆炸能量释放的最大例子，在此期间释放出高达1026焦耳的能量。太阳耀斑是空间天气的一个重要组成部分，然而，尽管它们具有重要意义，而且可从空间和地面上进行广泛的观测，但导致它们发生的确切机制仍然是一个悬而未决的问题。在太阳大气中测量的发射线通常显示的宽度超过了热多普勒线和仪器线的宽度。这些所谓的“非热”宽度的测量提供了关于发射等离子体状态的额外信息，包括可能存在的湍流，或由于压力和不透明度扩大而产生的影响。长期以来，X射线非热谱线宽度一直被观察到在耀斑活动期间显示出显著的增强，在冲激阶段早期达到峰值，并在耀斑达到峰值之前增加到数十分钟，这一结果已被来自Hinode EIS(Sarah Matthews是首席研究员)的EUV观测所证实和改进。这种对耀斑的早期反应表明，这一参数在耀斑的早期触发阶段具有潜在的重要意义。X射线和EUV谱线是在等离子体中形成的，其温度代表日冕的条件，标准模型表明能量在那里释放。然而，最近探索低层大气中形成的谱线轮廓的工作表明，轮廓形状与耀斑能量沉积之间存在相关性。然而，这些初步结果还没有与日冕线剖面进行比较，这将使能量释放和沉积过程能够在整个太阳大气中被跟踪，从而对耀斑开始和未来预测技术的可能性有新的见解。该项目最初将利用来自Hinode EIS和IRIS的光谱数据，纳入从EUI、SPICE和STIX仪器获得的来自太阳轨道器的新数据。所进行的研究也将是该太阳能集团目前正在开发的Solar C EUVST任务的准备工作的一部分，计划于2028年发射。因此，承担该项目的学生将有机会参加国际Hinode EIS和Solar C EUVST团队，包括参加团队会议和合作访问。

The Sun is our closest star, and with space now firmly established as part of our society's environment, its unique proximity has inescapable consequences for us. While solar radiation provides the energy source of our whole ecosystem, our understanding of how the variations in that radiation control, e.g. our climate, still contains huge gaps. As well as the long-term variations in the solar output, the Sun exhibits a cycle of activity the constituents of which are explosive events which release energy. This explosive energy release occurs on a myriad of scales, from nanoflares to huge eruptive flares, which are accompanied by the bulk eruption of plasma and magnetic field known as coronal mass ejections (CMEs) and whose impacts can be seen globally across the Sun and throughout the heliosphere. The most extreme of these events constitute the largest examples of explosive energy release within our solar system, during which upwards of 1026 J of energy is released. Solar flares comprise a key component of space weather, and yet despite their key importance and the extensive range of observations available from space and the ground, the precise mechanisms that lead to their onset remain an open question.Emission lines measured in the solar atmosphere routinely show widths in excess of both the thermal Doppler and instrumental line widths. Measurements of these so-called 'non-thermal' widths provide additional information on the state of the emitting plasma, including the possible existence of turbulence, or effects due to pressure and opacity broadening. X-ray non-thermal line widths have long been observed to show substantial enhancements during flaring activity, peaking early in the impulsive phase and increasing up to tens of minutes before the flare peak, a result that has been confirmed and refined with EUV observations from Hinode EIS (for which Sarah Matthews is the Principal Investigator). Such an early response to the flaring suggests that this parameter is potentially significant in the early trigger phase of flares. X-ray and EUV spectral lines are formed in plasmas with temperatures that represent conditions in the solar corona, where the standard model indicates energy is released. However, recent work exploring the profiles of spectral lines formed in the lower atmosphere suggests correlations between profile shape and flare energy deposition. These initial results have yet to be compared with coronal line profiles, however, which would enable the energy release and deposition process to be tracked throughout the entire solar atmosphere enabling new insights into flare onset and possibilities for future prediction techniques.The project will initially utilise spectroscopic data from Hinode EIS and IRIS, incorporating new data from Solar Orbiter as it becomes available from the EUI, SPICE and STIX instruments. The research undertaken will also form part of the solar group's preparatory work for the Solar C EUVST mission currently under development and scheduled for launch in 2028. The student undertaking this project would thus have the opportunity to participate both in the international Hinode EIS and Solar C EUVST teams, including attending team meetings and collaborative visits.