Global Nonpotential Models of the Solar Corona

日冕是一个高度结构化的环境，其大部分结构是由磁场造成的。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产生现象，如太阳细丝和日冕物质抛射（CME）。该项目将研究一个新的全球模型，用于从对流细胞向日冕注入磁能和螺旋度。该模型是基于Antiochos 2013的螺旋凝结过程，但扩展了该模型，使小规模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：螺旋凝结和太阳细丝太阳细丝勾勒出非势磁场在太阳表面的位置和传输。正因为如此，它们是太阳上自由磁能和螺旋度的形成、传输和定位的关键指标。太阳细丝的螺旋度可以很容易地根据其半球手性模式进行观测量化，其中右旋/左旋细丝含有负/正螺旋度在北半球/南半球占主导地位。这种模式，与观测到的异常相结合，为SAHC模型提供了观测约束。该WP的目的有两个：(i)在太阳周期时间尺度上对大、小规模能量和螺旋注入机制进行直接比较；（ii）用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，如果这两种机制中的任何一种占主导地位，以及这种主导地位是否在太阳周期中变化。WP2：螺旋凝结与磁链的形成和喷发。一旦通过太阳细丝对螺旋凝结的作用进行了观测测试，并确定了它的大小和纬度分布，第二项研究将考虑它对日冕物质抛射的影响。为了实现这一目标，将在太阳活动周期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（CME起始的关键组成部分）的形成速率和平衡损失率如何随观测约束水平上的螺旋凝结过程是否包括在内而变化。这是非常重要的，因为先前的研究表明，包含螺旋的双极的大规模出现只能占CME发生率的1/3。该研究将特别考虑：(i)通量绳的形成和失去平衡的位置，以及（ii）在螺旋凝结模型中，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。后者将通过直接将模拟与每年从模拟中获得的24,1个月期间的观测结果进行比较来验证。在两个完整的太阳周期内进行这样的采样将确定螺旋凝结是否是解释日冕物质抛射率的关键因素。已同意以下培训要求：(i)参加由太阳能集团举办的为期12周的博士培训计划，包括每周的理论和实践培训内容。（ii）参加高级太阳能理论模块。（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.