Global Nonpotential Models of the Solar Corona

日冕是一个高度结构化的环境，它的大部分结构是由于磁场。各种各样的机制将磁能和螺旋度注入日冕磁场，从而导致各种空间天气现象，如太阳细丝和日冕物质抛射(CME)。该项目将研究一种新的全球模型，用于从对流单体向日冕注入磁能和螺旋度。该模型是以安提奥乔斯2013年的螺旋凝聚过程为基础的，但对该模型进行了扩展，使得小尺度过程可以在太阳周期的时间尺度上应用于全球太阳。该项目涉及两个工作包。WP1：螺旋度、凝聚和太阳丝太阳丝概述了非位势磁场在太阳表面的位置和传输。因此，它们是太阳上自由磁能和螺旋度在全球范围内形成、传输和局部化的关键指标。太阳细丝中的螺旋度可以很容易地根据它们的手性半球模式进行量化，其中含有负/正螺旋度的右旋/左旋细丝在北半球/南半球占主导地位。这一模式与观测良好的异常相结合，为SAHC模型提供了观测约束。这个WP的目的有两个：(1)在太阳周期时间尺度上对大尺度和小尺度的能量和螺旋度注入机制进行直接比较；(2)通过对太阳细丝的观测，直接约束这些机制中的参数。这将使我们能够确定哪一种机制是主导的，如果这两种机制中的任何一种是主导的，以及这种主导是否在太阳周期中变化。WP2：螺旋度凝聚和磁通量绳的形成和喷发。一旦通过太阳细丝对螺旋度凝聚的作用进行了观测测试，并确定了其大小和纬度分布，第二项研究将考虑其对CME的影响。为了实现这一点，将在太阳周期23和24期间进行一系列数据驱动的模拟。这些模拟将考虑通量绳的形成和失去平衡的速率如何变化，这取决于是否包括观测约束水平上的螺旋度凝聚过程。通量绳是CME启动的关键组成部分。这一点极其重要，因为之前的研究表明，含有螺旋度的偶极的大规模出现只能占CME发生率的三分之一。特别是，研究将考虑：(I)通量绳的形成和失去平衡的位置，以及(Ii)在螺旋度凝聚模型中，这些速率如何随着注入速率的变化而变化。结果将直接与SOHO、STEREO和SDO的观测结果进行比较，以确定CME的数量和空间位置。后者将通过将模拟与每年从模拟中获得的24个月的观测值进行直接比较来进行测试。在两个完整的太阳周期内的这种采样将决定螺旋度凝聚是否是解释CMEs速率的关键因素。以下培训要求已达成一致：(I)参加由Solar Group举办的12周博士培训计划，该计划包括每周理论和实践培训元素。(Ii)参加高级太阳理论模块。(Iii)参加SMSTC课程。

The solar corona is a highly structured environment, where the majority of its structure is due to magnetic fields. A wide variety of mechanisms inject both magnetic energy and helicity into the coronal magnetic field, which results in a variety of Space Weather producing phenomena such as Solar Filaments and Coronal Mass Ejections (CME's). The project will investigate a new global model for the injection of magnetic energy and helicity into the corona from convective cells. The model is based on the Helicity Condensation process of Antiochos 2013 but extends the model such that the small-scale process can be applied globally on the Sun over time-scales of a solar-cycle. The project involves two work packages. WP1: Helicity Condensation and Solar FilamentsSolar filaments outline the location and transport of non-potential magnetic fields across the solar surface. Due to this, they are a key indicator for the formation, transport and localisation of free magnetic energy and helicity globally on the Sun. The helicity in solar filaments can be easily quantified observationally in terms of their hemispheric pattern of chirality, where dextral/sinistral filaments containing negative/positive helicity dominate in the northern/southern hemisphere. This pattern, in combination with the well observed exceptions, provide an observational constraint for the SAHC model. The aim of this WP is two-fold: (i) to carry out a direct comparison between the large- and small-scale energy and helicity injection mechanism over solar cycle time-scales; (ii) to constrain the parameters in these mechanisms directly with observations of solar filaments. This will allow us to determine which, if either of the two mechanisms are dominant and whether this dominance varies during the solar cycle. WP2: Helicity Condensation and the Formation and Eruption of Magnetic Flux ropes. Once the role of helicity condensation has been observationally tested through solar filaments, along with the determination of its magnitude and latitudinal profile, the second study will consider its consequences for CME's. To carry this out a series of data-driven simulations will be run over the period of solar cycle 23 and 24. These simulations will consider how the rate of formation and loss of equilibrium of flux ropes, a key component for the initiation of CME's, varies depending on whether or not the process of helicity condensation at observationally constrained levels is included. This is extremely important as previous studies have shown that the large-scale emergence of bipoles containing helicity can only account for a 1/3 of the CME occurrence rate. In particular the study will consider, (i) the locations of formation and loss of equilibrium of flux ropes and (ii) how these rates vary as the rate of injection varies in the helicity condensation model. Results will be directly compared with observations from SoHO, STEREO and SDO for both the number of CME's and their spatial location. The latter will be tested by directly comparing the simulation to observations over 24, 1-month periods taken yearly from the simulation. Such sampling over two full solar cycles will determine whether helicity condensation is the critical element in explaining the rate of CMEs.The following training requirements have been agreed:(i) To attend the 12 week PhD training program run by the Solar Group which involved weekly theoretical and practical training elements.(ii) Attend the Advanced Solar Theory module.(iii) Attend SMSTC courses.