Connecting coronal holes and open magnetic flux through observation and models of solar cycles 23 and 24
Lowder, Christopher Alan
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Coronal holes are regions of the Sun's surface that map the footprints of open magnetic field lines as they extend into the corona and beyond, into the heliosphere. Mapping their footprint 'dance' throughout the solar cycle is crucial for understanding this open field contribution to space weather. Coronal holes provide just this proxy. Using a combination of SOHO:EIT, SDO:AIA, and STEREO:EUVI A/B extreme ultraviolet (EUV) observations from 1996-2014, coronal holes can be automatically detected and characterized throughout this span, enabling long-term solar-cycle-timescale study. I have developed a routine to enable automated computer recognition of coronal hole boundaries from these EUV data. The combination of SDO:AIA and STEREO:EUVI A/B data provides a new viewpoint on understanding coronal holes. As the two STEREO spacecraft drift ahead of and behind the Earth in their orbits, respectively, they are able to peek 'around the corner', providing the ability to image nearly the entire solar atmosphere in EUV wavelengths, using SDO data in conjunction. On the far-side of the Sun, evolving open magnetic field structures impact space weather, despite being unobservable until rotating into view by Earth. By combining our numerical models of solar magnetic field evolution with coronal hole observations, comparison of far-side dynamics becomes possible. Model constraints and boundary conditions are more easily fine-tuned with these global observations. Long-term and transient coronal holes both play an important role as observational signatures of open magnetic field. Understanding the dynamics of boundary changes and distribution throughout the solar cycle yields important insight into connecting models of open magnetic field.