Waves and Flows: Linking the Solar Photosphere to the Corona

The Sun is one of the most important objects for humankind, with solar activity driving "space weather" and having a profound effect on the Earth's environment. We can directly see the effects of the Sun's powerful radiation through fascinating sights on Earth, such as the aurora borealis. However, it was the paradoxical nature of our Sun's temperature structure that first captivated my attention. One of the greatest scientific problems plaguing physicists is the fact that the outer atmosphere of our Sun is much hotter than its surface. Common sense leads us to believe that the local temperature will decrease as we move away from the Sun's 6000 K surface temperature. However, the corona, an atmospheric layer a few thousand km above the surface, radiates with a temperature exceeding one million degrees. Efforts to understand the heating processes responsible have remained at the forefront of observational and theoretical research for over 50 years, producing a popular class of theory known as wave heating. This mechanism suggests that waves, generated near the solar surface through the continual churning of plasma, propagate upwards, ultimately dissipating their energy and heating the Sun's outer atmosphere. A good analogy is to envisage ocean waves that travel vast distances across the sea before crashing on to shorelines, ultimately releasing immense quantities of energy in the process. However, the solar atmosphere is highly magnetic in nature. Magnetic field strengths often exceed 0.3 Tesla (similar in strength to modern open MRI scanners found in hospitals), resulting in wave modes becoming highly modified, and producing magneto-hydrodynamic (MHD) phenomena.

It is my desire to help improve our understanding of the physical processes at work within the Sun's atmosphere, an object that is so influential to life on Earth. A natural consequence of understanding the effects of solar magnetism will be the ability to predict solar activity, something that will ultimately allow us to protect ourselves from fierce outbursts of space weather. To pursue this crucial agenda, we need to observe and model the processes occurring in the Sun's atmosphere on their intrinsic scales. The UK has recently benefitted from a new breed of high-resolution solar instrumentation, including the Rapid Oscillations in the Solar Atmosphere (ROSA), Solar Dynamics Observatory (SDO), Hinode, and IRIS facilities, which will allow for the first time fundamental processes associated with the release of magnetic energy to be studied at an unprecedented level of detail. As an STFC Fellow, I will use modern ground- and space-based telescopes containing a wide assortment of high-resolution imaging and spectroscopic instrumentation. The observational component of my research will focus on the distinction of individual MHD waves, allowing key characteristics to be evaluated. These include the modes of oscillation (longitudinal, transverse, etc.), velocities, plasma densities, and temperatures, which can be combined to provide detailed energy estimates. The rate at which energy is dissipated will be compared to the heating requirements of the corona, with the exact role waves play in the heating of the Sun's corona unequivocally determined. Fundamental parameters deduced from high-resolution observations will be incorporated into advanced computer simulations. Large computer clusters, with 200+ CPUs, will be used to examine the 3D effects of waves on magnetic fields which intertwine the entire solar atmosphere. Characteristics associated with the waves will be studied in simulated solar structures, with forward modelling techniques implemented to allow direct comparisons with the physical observations to be undertaken, culminating in much refined heating models of the solar atmosphere. With the rapid advancements made in the field of solar physics over the last number of years, the ability to finally resolve the atmospheric heating paradox is now a reality.