Global Nonpotential Models of the Solar Corona

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 Filaments
Solar 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.