Modelling and Multi-wavelength Observations of Solar Flare Heating

我们的太阳被认为是一颗相当仁慈的恒星，让我们的星球沐浴在赋予生命的热量和光线中。但每隔11年左右，它的行为就会发生变化，从静止到动荡，然后又回来。在活动增加的时期，太阳扭曲和扭曲的磁场不断经历复杂的重新配置，以释放大量被压抑的能量。这些能量用于将太阳等离子体加热到数千万度的温度，并将粒子加速到接近相对论的速度。这种能量转换究竟是如何发生的仍然是一个悬而未决的问题，我的目标是在这次奖学金的过程中，通过利用目前可用的最先进的理论模型和观测数据集来解决这个问题。现代社会越来越依赖于越来越先进的技术。这些系统，如卫星通信、国家电网和全球定位系统(GPS)，都容易受到太阳行为变化的影响；通常被称为空间天气。空间天气通常包括两种现象：太阳耀斑和日冕物质抛射。日冕物质抛射是以每小时数百万英里的速度从太阳抛出的带电粒子云，在2-3天内到达地球，在那里它们可以干扰电力系统并产生壮观的极光，而太阳耀斑是强烈的辐射爆发，跨越从无线电波到伽马射线的整个电磁谱。这种辐射在短短8分钟内穿过太阳到地球的距离，紫外线(UV)成分被认为改变了我们大气的组成和动态。这可能会影响卫星在近地轨道上的运动，扰乱长波无线电通信，并影响GPS信号的传输。在太阳耀斑期间，大部分紫外线辐射是由色球发射的，色球是太阳可见光球层和脆弱的外层日冕之间的致密层。色球也是耀斑在初始阶段发出的大部分能量的地方，也是占据上面日冕环路的物质的来源。然而，释放的能量被转移到较低的太阳大气的机制仍然难以捉摸。人们通常认为，发射机制是一束高能电子，但这些粒子无法穿透到据信是最高能量发射的深处。其他提出的过程包括热传导、相对论离子、磁波或辐射回暖。幸运的是，发射出的大部分辐射都含有丰富的诊断信息，可以用来探测加热的等离子体。这使我们能够通过测量温度、密度、速度等的变化来区分不同的加热机制，并将它们与理论预测进行比较。虽然太阳耀斑可能会在整个光谱范围内发出辐射，但我们的光谱覆盖范围有些不足。大多数遥感仪器--无论是在太空中还是在地面上--通常被设计成观察非常有限的波长范围。因此，为了更完整地了解耀斑的太阳大气，不同仪器之间的协调观测至关重要。因此，这项研究的一个核心目标是搜索和编目各种仪器同时观测到的耀斑事件，并规划未来的协调观测活动。对于尚未观察到的部分频谱，应使用数值模拟的输出来填补空白。这将有助于为在项目过程中上线的仪器做准备。同样，由于星际介质的吸收，有些区域的恒星耀斑光谱是看不到的。这项研究的结果将有助于确定其他恒星的这种辐射的特征，特别是那些可能影响系外行星大气的辐射。

Our Sun is perceived to be a fairly benevolent star, bathing our planet in live-giving heat and light. But every 11 years or so, its behaviour changes, from quiescent to turbulent and back again. During periods of increased activity the Sun's twisted and contorted magnetic field continually undergoes episodes of complex reconfiguration to liberate vast quantities of pent-up energy. This energy goes into heating the solar plasma to temperatures of tens of millions of degrees and accelerating particles to near-relativistic velocities. Precisely how this energy conversation takes place remains an open question, and I aim to tackle this problem over the course of this Fellowship by capitalising upon the most advanced theoretical models and observational datasets currently available.Modern society is becoming increasingly dependent upon evermore advanced technologies. These systems, such as satellite communication, national power grids, and the Global Positioning System (GPS), are all susceptible to changes in the Sun's behaviour; more commonly referred to as space weather. Space weather typically comprises two phenomena: solar flares and coronal mass ejections (CMEs). CMEs are clouds of charged particles ejected off the Sun at millions of miles per hour, reaching the Earth in 2-3 days, where they can interfere with electrical systems and generate spectacular aurora, while solar flares are intense bursts of radiation that span the entire electromagnetic spectrum from radio waves to gamma-rays. This radiation traverses the Sun-Earth distance in just 8 minutes, and the ultraviolet (UV) component is known to change the composition and dynamics of our atmosphere. This can affect the motion of satellites in low Earth orbit, disrupt long-wave radio communication, and affect the transmission of GPS signals.During solar flares, much of the UV radiation is emitted by the chromosphere; a dense layer between the Sun's visible photosphere and the tenuous outer corona. The chromosphere is also where the bulk of a flare's energy emanates during its initial stages, and is the origin of material that occupies the overlying coronal loops. However, the mechanism by which the released energy gets transferred to the lower solar atmosphere remains elusive. It is commonly assumed that the delivery mechanism is a beam of high-energy electrons, and yet these particles are unable to penetrate to the depths at which the most energetic emission is believed to originate. Other proposed processes include heat conduction, relativistic ions, magnetic waves, or radiative backwarming. Fortunately, much of the radiation emitted contains a wealth of diagnostic information with which to probe the heated plasma. This allows us to distinguish between various heating mechanisms by measuring changes in temperature, density, velocity, etc, and comparing them to the predictions of theory.While solar flares may emit radiation across the entire spectrum, our spectral coverage is somewhat lacking in parts. Most remote sensing instruments - both in space and on the ground - are often designed to look at a very limited wavelength range. Therefore in order to build a more complete picture of the flaring solar atmosphere, coordinated observations between different instruments are crucial. A core goal of this research is therefore to search for and catalog flaring events observed by a variety of instruments simultaneously, as well as planning future coordinated observing campaigns. For parts of the spectrum that are not yet observable, outputs from numerical simulations shall be used to fill in the gaps. This will help to prepare for instrumentation that will come online during the course of the project. Similarly, there are regions of stellar flare spectra that are unobservable due to absorption by the interstellar medium. The outcomes of this research shall assist in characterising this emission on other stars, especially that which can affect exoplanet atmospheres.