Nanoflares: Explosive Heating of our Sun's Atmosphere

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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 is the paradoxical nature of our Sun's temperature structure that continues to frustrate scientists. 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 flare heating. This mechanism suggests that turbulent plasma processes cause the magnetic field lines embedded in the Sun's atmosphere to become twisted and stretched. The process of magnetic reconnection results in these strained field lines returning to a more stable configuration, but releasing huge quantities of energy in the process. A large-scale solar flare can release in excess of 10^25 Joules of energy during a single event; the equivalent of over 5 million times more than the total combined energy of all atomic bombs ever detonated. However, these large events are too rare to support the continuously elevated temperatures in our Sun's outer atmosphere. Instead, it is believed that small-scale flares, or "nanoflares" with an equivalent energy of a single modern atomic bomb, may occur with such regularity that they can provide a continuous basal background heating. 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 flares 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 these explosive processes occurring in the Sun's atmosphere on their intrinsic scales. A new breed of highly sensitive scientific cameras will allow for the first time fundamental processes associated with the release of magnetic energy to be studied at an unprecedented level of detail. With an STFC Research Grant, a post-doctoral researcher will employ one of these modern pieces of equipment to image a variety of magnetic structures in the Sun's atmosphere with frame rates approaching 100 per second. The intensities of all structures will be monitored, with the characteristics of small-scale nanoflares evaluated. An in-depth examination of the regions where nanoflare activity is omnipresent will allow the processes at work to be compared precisely to the underlying magnetic field configurations. Fundamental parameters deduced from high-resolution observations will be incorporated into advanced computer simulations. Large computer clusters, often exceeding 200 CPUs, will be used to examine the effects of sub-resolution nanoflare activity on the intensity profiles extracted from the high-resolution observations. A direct comparison between the simulations and the observations will be undertaken, with key nanoflare characteristics determined, including the reconnection rates, the total energy released, and the plasma relaxation time scales. For the first time, the conditions promoting nanoflares will be understood, with the specific role they play in the heating of our Sun's atmosphere evaluated.