Research interests summary

- Long-term evolution of active regions.

- Evolution of magnetic fields leading to onset of coronal mass ejections.

- Formation and magnetic topology of sigmoids.

The Sun provides us with a unique opportunity to study fundamental physical processes which control how a star lives. It is important to study the Sun because it has such a major impact on the Earth's atmosphere and magnetic field, and therefore on our lives. Many of the Sun's effects go unnoticed but some, such as the northern lights, are enjoyed by many.

My research programme addresses key questions related to the evolution of the Sun's magnetic field. In particular, I am interested in coronal mass ejections; huge eruptions of magnetic field and hot gases that somehow break free from the Sun and speed into the Solar System at 100's km/s.

Coronal mass ejections are seen as clouds of outward moving material when the Sun is eclipsed, as in the top-left image above. The ejections can also be seen as so-called filament eruptions from just above the visible solar surface. I study the magnetic source regions of coronal mass ejections with a view to understanding the changes in the Sun's magnetic field which trigger them.

Observations over the last 10 years or so have suggested that bright 'S' shaped loops, as shown in the top-right image above, are sometimes present on the Sun. These 'S' shaped loops are an indicator that the region is about to produce a coronal mass ejection. My obervational studies of these regions have enabled us to understand their magnetic structure. This is needed for us to understand the physical processes which trigger and drive coronal mass ejections. My recent work (Green and Kliem, 2009) provided evidence of bundles of magnetic fields which form a rope structure and in Green, Kliem and Wallace (2011) we studied how much magnetic field is contained in such a rope.

Today we know that the Sun's hot atmosphere extends billions of km into space and is filled with magnetic fields which have their origin deep inside the Sun. This means that the Earth is sitting in the Sun's extended atmosphere. The result of this is that we are being constantly bombarded by charged particles and magnetic fields emanating from the Sun. The strength and complexity of the magnetic field varies with the so-called solar cycle, which lasts roughly 11 years. Recently, we have observed a very extended solar minimum phase where the Sun became very inactive and its magnetic field diminished. This sparked a lot of interest across the science community as well as the public. The Sun's quiet nature has no doubt had a corresponding affect on the Earth, but this hasn't been able to counteract the current global warming.