Research


The Sun provides a unique opportunity to study fundamental physical processes which control how a star lives with the added importance that it needs to be understood as 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.

Lucie’s research looks at the evolution of the Sun’s magnetic field and how our star can drive what is known as ‘space weather’ here on Earth. The Sun produce coronal mass ejections – huge eruptions of magnetic field and electrically charged gas – that somehow break free from the Sun and speed into the Solar System at 100s km/s. Coronal mass ejections are seen as clouds of outward moving material when the Sun is eclipsed. The ejections can also be seen as so-called filament eruptions from just above the visible solar surface through specialist amateur telescopes. Lucie studies the magnetic source regions of coronal mass ejections with a view to understanding the changes in the Sun’s magnetic field which trigger them.

Over the last few years she has been interested in bright ‘S’ shaped structures that are sometimes present on the Sun. These ‘S’ shapes are an indicator that the Sun is about to produce a coronal mass ejection. Lucie’s observational studies of these regions have enabled scientists to further understand their magnetic structure which is needed to understand the physical processes which trigger and drive coronal mass ejections. The video below shows one of the S-shaped regions studied by Lucie that was observed with the X-ray telescope onboard the Hinode satellite.

Origin of a coronal mass ejection at the Sun from luciegreen on Vimeo.

Green and Kliem (2009) provided evidence that the S shapes are twisted bundles of magnetic fields and have a rope structure and Green, Kliem and Wallace (2011) studied how much magnetic flux is contained in such a rope. They found a much higher value than models predicted which started to be reconciled in Savcheva, Green et al. (2012).

Lucie’s work on flux ropes was extended through a collaboration with Sergei Zharkov and Sarah Matthews who analyse and model the Sun’s seismic activity. Over the last decade, it has become well established that beams of particles accelerated during a solar flare can travel into the Sun and produce a sunquake (a short burst of seismic activity analagous to an earthquake). This collaboration found that sunquakes can also be triggered during the eruption of magnetic flux ropes. The research showed that as a magnetic flux rope accelerates away from the Sun, the rapidly changing magnetic field anchored in the solar surface may play an important role in the onset of the sunquake. These results highlight the important role of the magnetic field in the triggering of sunquakes.

The view of the Sun given to us by space-age technology shows that the space around the Sun is far from empty. As well as blasting out coronal mass ejections, the Sun’s atmosphere itself extends billions of km into space – drawn out by a strong solar wind. The Voyager 1 space probe became the first human-made object to directly locate the edge of the Sun’s atmosphere when it passed into interstellar space in 2012 after having travelled 15 billion km from us. The Earth is sitting directly in this wind which provided the energy to drive space weather at Earth.

The solar wind carries with it magnetic fields, which have their origin deep inside the Sun, as well as electrically charged particles out into the Solar System. The strength and complexity of the Sun’s 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. Since then the Sun’s activity has picked up and has plenty of coronal mass ejections our way.