Multi-scale modelling of heating and particle acceleration in twisted magnetic fields in solar flares and coronal heating

太阳耀斑和日冕加热扭曲磁场中的加热和粒子加速的多尺度建模

基本信息

批准号：
ST/P000428/1
负责人：
Philippa Browning
金额：
$ 45.34万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FP000428%2F1
关键词：
Multi scale modelling heating particle

项目摘要

Solar flares are dramatic and complex events, which give off electromagnetic radiation in almost all wavelength bands across the spectrum, and also directly emit high energy particles into space. They are of great interest in their own right, as examplars of fundamental physical processes which take place across the universe - and because of their significant effects on the Earth's space environment through "space weather". The high-energy particles and electromagnetic radiation from flares can damage satellites as well as power systems on the Earth, and are potentially hazardous to astronauts. It is well-established that the primary energy release mechanism is the process of magnetic reconnection. However, there are major outstanding issues to be resolved: in particular, the origin of the large numbers of high energy (non-thermal) ions and electrons. Whilst much new light has been shed on the properties of these particles by recent observations, especially from the Hard X-ray imaging telescope RHESSI, new observations have also posed new challenges to theory and modelling. The vast range of length scales involved - from the global scales of mega-metres down to fundamental plasma scale lengths of metres - makes modelling a particularly difficult task, and no single model can encompass all features.Another long-standing mystery is to explain the existence of a hot X-ray corona - whose temperature (millions of degrees) greatly exceeds the surface temperature (a few thousand degrees). One very promising scenario is that coronal heating arises from the combined effect of many very small flare-like events, known as nanoflares. Thus, the fundamental energy release process is magnetic reconnection, as in larger scale solar flares. In order to distinguish between different candidates for coronal heating, it is necessary to predict observable signatures, such as the properties of energetic particles, the temperature distribution, and plasma flows.Twisted magnetic fields provide a reservoir of free magnetic energy which could be dissipated into heating, and such twisted fields are likely to be very common in the solar corona - both as large-scale structures and on smaller scales. We have previously shown that single twisted flux ropes may rapidly release stored magnetic energy if their twist is sufficiently large for onset of the ideal kink instability - this generates small-scale fragmented currents sheets, with efficient plasma heating and particle acceleration through magnetic reconnection. We have developed a powerful set of tools, coupling test-particles to 3D magnetohydrodynamic simulations, and forward-modelling observable signatures such as soft and hard X-ray emission.In this project, we will build on this work to develop an interlinked hierarchy of models for energy release in twisted magnetic flux ropes, from more idealised 2D models to complex and more realistic larger-scale models. We will develop and exploit an innovative new modelling approach called "reduced kinetics" which bridges the gap between kinetic and fluid approaches. We will use this, and advanced test-particle codes coupled with magnetohydrodynamic simulations, to study both plasma heating and particle acceleration in forced reconnection, driven by an external disturbance, focussing on the merger of twisted flux ropes with the reconnecting current sheet in both 2D and 3D.We will also investigate thermal and non-thermal plasma in more realistic 3D configurations, including curvature and a realistic atmosphere. As well as single unstable loops, we will explore interactions between loops, especially a recently-discovered "avalanche" process whereby one unstable loop may trigger energy release from many stable neighbours. Observable signatures, including microwave emission, will be predicted, so that different scenarios can be compared and tested against observations.

太阳耀斑是戏剧性且复杂的事件，它在整个光谱上几乎所有波长带中散发电磁辐射，并且还直接将高能量颗粒散发到太空中。它们本身具有极大的兴趣，因为在宇宙中发生的基本物理过程的检查和通过“太空天气”对地球太空环境产生了重大影响。耀斑的高能颗粒和电磁辐射会损坏卫星以及地球上的动力系统，并且可能对宇航员危害。公认的是，主要的能量释放机制是磁重新连接的过程。但是，有一些重大的问题要解决：特别是，大量高能（非热）离子和电子的起源。尽管最近观察到了这些粒子的特性，尤其是从硬X射线成像望远镜Rhessi上散发出了许多新的光，但新观察也对理论和建模构成了新的挑战。所涉及的广泛长度范围 - 从大型米特的全球尺度到基本的等离子尺度的仪表 - 使建模成为一个特别艰巨的任务，没有一个单一的模型可以涵盖所有功能。另一个长期以来的神秘是要解释热的X射线电晕的存在 - 其温度（千万度）超过了表面温度（数百万度）。一个非常有前途的场景是，冠状加热是由许多非常小的耀斑样事件（称为纳米丝）的综合作用。因此，基本能量释放过程是磁重新连接，如大规模太阳耀斑所示。为了区分冠状加热的不同候选者，有必要预测可观察到的特征，例如能量颗粒的特性，温度分布和等离子体流动。两个磁场可提供的自由磁能储存库可以使可以散布到加热中，并且在Solar Corona中很常见，并且在较大的corno corona中都非常常见。我们以前已经表明，如果单个扭曲绳索的扭曲足够大，可以迅速释放储存的磁能，以发作理想的扭结不稳定性 - 这会产生小规模的碎片电流表，并通过磁重新连接具有有效的等离子体加热和颗粒加速。我们已经开发了一组强大的工具，将测试粒子耦合到3D磁水动力学模拟以及前向模型可观察的签名，例如柔软而硬的X射线发射。在此项目中，我们将在这项工作中建立这项工作，以开发一个相互链接的层次结构，以在扭曲的磁通型模型中进行更理想化的模型，以更高的模型，更高的模型和更具现实的模型，并更具现实的模型，并更加现实地使用了更为现实的模型，并更具现实的模型。我们将开发并利用一种创新的新建模方法，称为“减少动力学”，该方法弥合了动力学方法和流体方法之间的差距。我们将使用它，高级测试粒子代码以及磁流失动力学模拟，研究在外部干扰的驱动中，在强迫重新连接中的血浆加热和颗粒加速度，重点关注扭曲磁通绳的合并，并在2D和3D中均应进行重新连接。一种现实的气氛。除了单个不稳定的循环外，我们还将探索循环之间的相互作用，尤其是最近发现的“雪崩”过程，从而，一个不稳定的环路可能会触发许多稳定的邻居的能量释放。可以预测可观察到的特征，包括微波排放，以便可以比较不同的情况与观察结果进行测试。