I am working on mathematical modelling of the magnetic field in the Solar corona, supervised by Dr D.H. Mackay and Prof E.R. Priest. Initially this has been motivated by the hemispheric pattern of solar filaments (see my recent poster for a summary).
A major part of my work has been to develop a new global simulation of the magnetic field evolution in the corona. The magnetic field plays a dominant role in the evolution of the corona, being responsible for both stable (e.g. quiescent filaments, coronal holes) and eruptive (e.g. flares, CMEs) phenomena. Unfortunately this magnetic field is usually impossible to measure directly, because of the very low particle density in the corona.
The magnetic field in the photosphere (the Sun's visible surface) may, however, be measured with some accuracy, and such observations are taken on a regular basis. We have developed a new technique for the accurate simulation of this photospheric field over a period of months, without having to reset to the observed field. This allows us to compute the evolution of the coronal magnetic field, as it changes in response to photospheric motions.
Snapshot from one of our simulations, showing radial magnetic field on the photosphere (white positive, red zero, black negative), and selected coronal field lines traced from points in the plane of the screen.
Download an mpeg movie of the simulation.
Our model represents a significant improvement over so-called "potential field" models of the corona, which do not allow any electric currents to flow. In our case the coronal field relaxes toward states where the Lorentz force vanishes, evolving through a sequence of more general "force-free fields". These allow for the storage of free magnetic energy, and also for electric currents parallel to the magnetic field lines.
In addition, potential field models use independent extrapolations of the coronal field at different times, whereas our model can follow the continuous evolution and build-up of magnetic helicity and shear in the coronal field.