Nature of project: **data analysis**, software

Available to students on full-time physics degree schemes or joint students.

The magnetic field of the solar corona is the most important factor dictating the structure of the corona and therefore the structure of the whole heliosphere. Despite its importance, it cannot be observed directly (except in a few isolated cases), therefore its shape must be estimated from models. The most simple model is a potential field source surface model (PFSS), where detailed observations of the photospheric field is the inner boundary condition, and the assumption that the coronal field becomes radial at a given height (usually ~2Rs above the Sun) gives the outer boundary condition. These conditions, and the assumption of a force-free corona, leads to an unique solution for the magnetic field.

For a given set of dates, the student will use established software to calculate PFSS models of the solar corona. From these, the student will use other software to calculate a value called 'convergence' from the B-field. These can be directly compared to electron density maps of the corona provided by Dr. Morgan. The student will make comparisons between the maps for several periods over the last solar cycle and attempt to interpret the similarities or differences seen.

*A successful project will develop beyond the above in one/some of the following directions:*

The natural extension to the core project is to write software to give a quantitative value for the difference between the position of streamers as seen in the tomography maps and the distribution of magnetic structures in the PFSS model. There is scope also to extend the study to a long time period, covering several years.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

*Additional scope or challenge if taken as a Year-4 project:* The student will write software to make quantitative comparisons of structure seen in the density and magnetic field maps. This will mean use of common image processing methods to identify high-density features in both maps (magnetic or electron), plus the additional challenge of calculating the geometrical differences seen in structure.

Please speak to **Huw Morgan** if you consider doing this project.

*Initial literature for students:*

- Morgan, H., An Atlas of Coronal Electron Density at 5Rs. II. A Spherical Harmonic Method for Density Reconstruction. The Astrophysical Journal Supplement Series 242, 3 (2019)
- Huw Morgan and S. Rifai Habbal, Observational aspects of the 3D coronal structure over a solar activity cycle, Astrophysical Journal, 710, Issue 1, pp.1-15, 01/2010
- Wang, Y.-M., & Sheeley, N. R., On Potential Field Models of the Solar Corona. 1992, ApJ, 392, 310

The main difficulty with the main project is setting up the software and data download using IDL - most of the software is already written.

The student will need to learn basic unix skills and IDL calls.

milestone | to be completed by |
---|---|

Setting up of software | Christmas |

Processing of several case studies | end of February |

Comparison with tomography maps | mid-March |

Completed work (3rd year), analysis software (additional challenge) | Easter |