Understanding global eigenmodes 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 magnetoacoustic wave motion from below the solar surface up into the dynamic layers of the outer atmosphere. Furthermore, many of the sunspots observed appear to have distinct eigenmodes, whereby the entire sunspot is observed to oscillate coherently with the same frequency. Why is this? What underlying physical mechanisms allow for a structure much larger than the Earth to oscillate uniformly across its entire surface? The challenge is to understand how both (1) the shape of the sunspot, and (2) its plasma composition with atmospheric height produces the signatures we see in the observations. For example, do sub-surface drivers fuel the eigenmodes we observe? Or do waves trapped in a solar resonance cavity (similar to that of an acoustic guitar) provide the creation of these powerful effects? 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 wave signals.

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. Spectropolarimetric observations will be acquired to allow the Stokes vectors that define the magnetic polarization 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 eigenmodes, with the energetics and thermal gradients established through spectroscopy and spectral imaging techniques.

The PhD student will develop and compare advanced wave detection and tracking algorithms with cutting-edge observational datasets, in order to characterise and ultimately understand the behaviours, energetics and roles magnetohydrodynamic waves play in the creation of coherent oscillations in sunspot atmospheres. 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.

If you have any questions, please contact Prof. David Jess.

Contact:

Lead supervisor (QUB): Prof. David Jess (d.jess@qub.ac.uk)

Co-supervisor (QUB):  Dr. Samuel Grant (samuel.grant@qub.ac.uk)