Energy Dissipation in Solar Physics:

Non-linear shock development in the Sun’s most powerful magnetic fields


Background

The Sun is one of the most important astronomical objects for humankind, with solar activity driving “space weather” and having a profound effect on the Earth’s environment. It provides a unique laboratory where the study of interacting plasmas with concentrated magnetic fields can be readily achieved over an enormous range of scales. A large fraction of the phenomena that exists in the dynamic layers of our Sun is intrinsically linked to the strong magnetic fields that permeate through its entire atmosphere. It is believed that the building blocks of large-scale atmospheric structuring are present at the base (photosphere) of the solar atmosphere, and that these structures unlock the mechanisms that promote efficient energy transfer through the Sun’s layers. A prime example are sunspots, which create towering coronal loop structures extending many hundreds of thousands of km away from the visible solar surface.

The powerful magnetic fields that are embedded within sunspot atmospheres provide an efficient mechanism to channel acoustic wave motion from below the solar surface up into the dynamic layers of the outer atmosphere. However, once the waves leave the high-density confines of the Sun’s photosphere, non-linear effects begin to take hold. In order to conserve energy flux in the atmosphere’s diminishing density, the wave amplitudes need to increase. At a certain point, the velocity amplitudes of the waves exceed the local sound speed, causing the waves to transform into highly non-linear shocks. These shocks have the potential to heat the solar atmosphere by thousands of degrees, thus transferring huge quantities of energy into the local environment. Furthermore, the shock-forming waves are prone to conversion into other types of magnetohydrodynamic phenomena, thus opening the door for other more-elusive forms of shock formation, such as intermediate and Alfvén shocks. Such shock types are currently at the forefront of observational and theoretical study, with inconclusive evidence regarding their existence. In order to probe such plasma effects at the diffraction limit of high-resolution telescopes requires the use of novel and computationally intensive image processing techniques, along with theoretical interpretation of the observed shock signals.

The project

The project will combine observational, theoretical, computational and statistical techniques in an academic environment. The student will make extensive use of current- and next-generation telescope and computing facilities, including the ground-based Rapid Oscillations in the Solar Atmosphere (ROSA) instrument that has been designed in-house at QUB and commissioned on the Dunn Solar Telescope, New Mexico, USA. Space-based instruments such as the Solar Dynamics Observatory, Hinode, and the NASA IRIS spacecraft will be used in conjunction with ground-based facilities to obtain multi-wavelength data sets covering a multitude of atmospheric layers between the photosphere and corona. Spectro-polarimetric observations will be acquired to allow the Stokes vectors that define the magnetic polarisation of the incident light to be inverted, thus providing remote sensing of the sunspot’s magnetic field vectors. These magnetic field vectors will be examined for the presence of shocks, with the energetics and thermal gradients established through spectroscopy and spectral imaging techniques.

The PhD student will develop and compare advanced shock detection and tracking algorithms with cutting-edge observational datasets, in order to characterise and ultimately understand the behaviours, energetics and roles magnetohydrodynamic shocks play in providing thermal energy deposition across different layers of our Sun’s atmosphere. Such techniques may include longitudinal analysis, three-dimensional Fourier filtering, non-local de-noising, among others, to best improve the dynamic range of the observed signals, while maintaining photometric accuracy. It is anticipated that the timely nature of this project will position the student in an ideal position to make new discoveries and drive forward research in astrophysical disciplines.

Funding is provided within the PhD studentship for travel to, and participation in, key astrophysics conferences throughout the project. It is envisaged that the student will actively engage in both national and international meetings and workshops, where they will disseminate their cutting-edge research to a global audience. As a result, the ability to travel and work within a team environment is a crucial component of the research objectives.

More info

Supervisor: Dr. David Jess

public/phds2019/2019_sunspots_jess.txt · Last modified: 2018/12/21 11:17 by David Jess

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