Determining the fundamental nature of the solar atmosphere: applying Bayesian analysis methods to Hinode observations

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To say the Sun is important really is an understatement- we are here because our closest star provides the necessary light and heat required for life on Earth. We are in a golden era of solar-terrestrial research at this time with several major satellite missions revolutionising our understanding of the flow of energy from the Sun to the Earth. In particular, a joint Japanese, British and American satellite called Hinode (meaning 'sunrise' in Japanese) was launched in late 2006. Using a combination of instruments that observe the light from the Sun in optical, Extreme Ultraviolet and X-ray wavelengths, Hinode will study the intimate relationship between the Sun's magnetic field and its outer atmospheric layers. One of the remaining unresolved questions in solar physics is why the temperature of this outer atmosphere rises from 5780 K at the photosphere (where the visible light originates) to millions degrees in the outermost parts- the corona. Clearly as you move away from a heat source (in this case the energy generated by nuclear reactions at the core of the Sun), the temperature should fall away. Some additional heating must be dumping extra energy directly into the corona to create this counter-intuitive temperature rise. Several mechanisms have been suggested which are all centred around the Sun's magnetic field. However, there is as yet no scientific consensus on the specific details on how this 'coronal heating problem' can be solved. In particular, a significant proportion of the radiation emitted from the solar corona is concentrated along well-defined loop-like arches. These loops are the basic structural elements of the atmosphere and coincide with the magnetic field as it rises out though the surface of the star, 'trapping' the electrified gases (the plasma) along its length. The research proposed in this application seeks to use Hinode to probe the corona like never before. Part of the work will deal with detecting and measuring 'magnetic sound waves' (termed magnetoacoustic oscillations) as they travel along loops, carrying energy through the solar atmosphere. Also, by using techniques in solar spectroscopy, we will measure remotely the temperature and density along loops to help us further understand the nature of the corona and where this extra energy could be being deposited. To fully examine our observations, we will use a set of statistical tools called Bayesian analysis methods- these techniques allow us to add into our investigations as much prior information or knowledge of the loops as possible. This will be a new way in Solar Physics to help us compare our theoretical models with these latest satellite observations.