Nanoflares: Explosive Heating of our Sun's Atmosphere

太阳是人类最重要的天体之一，太阳活动推动着“空间天气”，并对地球环境产生深远影响。我们可以通过地球上引人入胜的景象，如北极光，直接看到太阳强大辐射的影响。然而，太阳温度结构的矛盾性质仍然让科学家们感到沮丧。困扰物理学家的最大科学问题之一是，太阳的外层大气比其表面热得多。常识使我们相信，当我们远离太阳6000K的表面温度时，当地的温度将会下降。然而，日冕，地表上方几千公里的大气层，辐射温度超过一百万度。50多年来，理解相关加热过程的努力一直处于观测和理论研究的前沿，产生了一种被称为耀斑加热的流行理论。这一机制表明，湍流的等离子体过程导致嵌入太阳大气中的磁力线扭曲和拉伸。磁重联的过程导致这些应变的场线返回到更稳定的构型，但在这个过程中释放了大量的能量。一次大规模的太阳耀斑可以在一次事件中释放超过10^25焦耳的能量；相当于所有原子弹引爆的总能量的500多万倍。然而，这些大型事件太罕见了，不足以支持太阳外层大气中持续升高的温度。相反，人们认为，小规模耀斑或相当于一枚现代原子弹能量的“纳米耀斑”可能会以如此规律性的方式发生，以至于它们可以提供持续的基础背景加热。我的愿望是帮助我们更好地了解太阳大气层内的物理过程，太阳大气层是一个对地球上的生命如此有影响的天体。了解太阳耀斑的影响的自然结果将是预测太阳活动的能力，这最终将使我们能够保护自己免受猛烈的太空天气爆发的影响。为了推进这一至关重要的议程，我们需要观察太阳大气中发生的这些爆炸性过程，并对其进行内在尺度的模拟。一种新型的高灵敏度科学相机将首次能够以前所未有的详细程度研究与磁能释放相关的基本过程。有了STFC研究资助，博士后研究人员将使用这些现代设备之一来成像太阳大气中的各种磁结构，帧速率接近每秒100。将监测所有结构的强度，并评估小规模纳米耀斑的特征。对纳米耀斑活动无处不在的区域进行深入研究，将使工作中的过程能够准确地与潜在的磁场配置进行比较。从高分辨率观测得出的基本参数将被纳入先进的计算机模拟。通常超过200个中央处理器的大型计算机集群将被用来检查亚分辨率纳米耀斑活动对从高分辨率观测中提取的强度分布的影响。将在模拟和观测之间进行直接比较，确定关键的纳耀斑特征，包括重联率、释放的总能量和等离子体弛豫时间尺度。将首次了解促进纳米耀斑的条件，并评估它们在太阳大气加热中所起的具体作用。

The Sun is one of the most important objects for humankind, with solar activity driving "space weather" and having a profound effect on the Earth's environment. We can directly see the effects of the Sun's powerful radiation through fascinating sights on Earth, such as the aurora borealis. However, it is the paradoxical nature of our Sun's temperature structure that continues to frustrate scientists. One of the greatest scientific problems plaguing physicists is the fact that the outer atmosphere of our Sun is much hotter than its surface. Common sense leads us to believe that the local temperature will decrease as we move away from the Sun's 6000 K surface temperature. However, the corona, an atmospheric layer a few thousand km above the surface, radiates with a temperature exceeding one million degrees. Efforts to understand the heating processes responsible have remained at the forefront of observational and theoretical research for over 50 years, producing a popular class of theory known as flare heating. This mechanism suggests that turbulent plasma processes cause the magnetic field lines embedded in the Sun's atmosphere to become twisted and stretched. The process of magnetic reconnection results in these strained field lines returning to a more stable configuration, but releasing huge quantities of energy in the process. A large-scale solar flare can release in excess of 10^25 Joules of energy during a single event; the equivalent of over 5 million times more than the total combined energy of all atomic bombs ever detonated. However, these large events are too rare to support the continuously elevated temperatures in our Sun's outer atmosphere. Instead, it is believed that small-scale flares, or "nanoflares" with an equivalent energy of a single modern atomic bomb, may occur with such regularity that they can provide a continuous basal background heating. It is my desire to help improve our understanding of the physical processes at work within the Sun's atmosphere, an object that is so influential to life on Earth. A natural consequence of understanding the effects of solar flares will be the ability to predict solar activity, something that will ultimately allow us to protect ourselves from fierce outbursts of space weather. To pursue this crucial agenda, we need to observe and model these explosive processes occurring in the Sun's atmosphere on their intrinsic scales. A new breed of highly sensitive scientific cameras will allow for the first time fundamental processes associated with the release of magnetic energy to be studied at an unprecedented level of detail. With an STFC Research Grant, a post-doctoral researcher will employ one of these modern pieces of equipment to image a variety of magnetic structures in the Sun's atmosphere with frame rates approaching 100 per second. The intensities of all structures will be monitored, with the characteristics of small-scale nanoflares evaluated. An in-depth examination of the regions where nanoflare activity is omnipresent will allow the processes at work to be compared precisely to the underlying magnetic field configurations. Fundamental parameters deduced from high-resolution observations will be incorporated into advanced computer simulations. Large computer clusters, often exceeding 200 CPUs, will be used to examine the effects of sub-resolution nanoflare activity on the intensity profiles extracted from the high-resolution observations. A direct comparison between the simulations and the observations will be undertaken, with key nanoflare characteristics determined, including the reconnection rates, the total energy released, and the plasma relaxation time scales. For the first time, the conditions promoting nanoflares will be understood, with the specific role they play in the heating of our Sun's atmosphere evaluated.