Theses and Dissertations at Montana State University (MSU)
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Item Modeling the effects of flare energy release and transport through chromospheric condensation and ultraviolet coronal emission(Montana State University - Bozeman, College of Letters & Science, 2022) Ashfield, William Henry, IV; Chairperson, Graduate Committee: Dana W. Longcope; This is a manuscript style paper that includes co-authored chapters.Solar flares arise from the release of magnetic free energy through reconnection. A fraction of this energy travels from the corona to the lower solar atmosphere, heating the plasma and driving downflows -- chromospheric condensations -- critical to our understanding of flare energetics. While flare models with impulsive energy injections have successfully reproduced observed chromospheric responses, they typically focus on heating via electron beam deposition, neglecting other modes of energy transport. Observations of long-duration coronal emission in the extreme ultraviolet have further indicated a two-phase energy release process: impulsive energy deposition followed by persistent low-rate heating. As flare energy release and transport are measured by the indirect signatures of condensation and coronal emissions, flare models must account for these phenomena' behavior to infer the characteristics of reconnection. We first investigated the chromospheric response to a constant flare energy flux using a thermal flare model driven by in-situ coronal heating. An analytical expression for the condensation velocity was developed and found to be well described by the observed characteristic properties, allowing condensation to serve as a diagnostic for both the energy flux at the reconnection site and the pre-flare density scale height of the chromosphere. These results were tested on condensations observed in Si IV 1403 ?A spectral line redshifts. A Gaussian heating profile, inferred from footpoint UV emission corresponding to the measured downflows, was used to drive a one-dimensional simulation from which Si IV spectra were synthesized. Although the synthetic velocity evolution agreed reasonably well with observation, thus providing evidence for our model's validity, the condensation's timescale was found to be independent of the time scale of the energy release. To address coronal EUV emission signatures, long-duration flare heating was modeled through the slow dissipation of turbulent Alfven waves. Motivated by observations of supra-arcade downflows, the waves were initiated by retracting newly-reconnected flux tubes through a current sheet and dissipated through their non-linear interaction. EUV lightcurves synthesized from simulation results reproduced emissions that decayed in 40 minutes. This model, created self-consistently from reconnection-powered flare energy release, offers a possible explanation for the outstanding problem of persistent flare emission.Item Stigmatic spectroscopy of the solar atmosphere in the vacuum-ultraviolet(Montana State University - Bozeman, College of Letters & Science, 2020) Courrier, Hans Thomas; Chairperson, Graduate Committee: Charles C. Kankelborg; Charles C. Kankelborg was a co-author of the article, 'Using local correlation tracking to recover solar spectral information from a slitless spectrograph' in the journal 'Journal of astronomical telescopes and imaging systems, SPIE' which is contained within this dissertation.; Charles C. Kankelborg, Bart De Pontieu and Jean-Pierre Wulser were co-authors of the article, 'An on orbit determination of point spread functions for the interface region imaging spectrograph' in the journal 'Solar physics' which is contained within this dissertation.; Charles C. Kankelborg, Amy R. Winebarger, Ken Kobayashi, Brent Beabout, Dyana Beabout, Ben Carroll, Jonathan W. Cirtain, James A. Duffy, Carlos Gomez, Eric M. Gullikson, Micah Johnson, Jacob D.Parker, Laurel A. Rachmeler, Roy T. Smart, Larry Springer and David L. Windt were co-authors of the article, 'The EUV snapshot imaging spectrograph (ESIS)' which is contained within this dissertation.The solar atmosphere presents a complicated observing target since tremendous variability exists in solar features over a wide range of spatial, spectral, and temporal scales. Stigmatic spectrographs are indispensable tools that provide simultaneous access to spatial context and spectroscopy, enabling the diagnosis of solar events that cannot be accomplished by imaging or spectroscopy alone. In this dissertation I develop and apply a novel technique for on orbit spectrograph calibration, recover co-temporal Doppler shifts of widely spaced solar features, and describe a new design for a slitless solar spectrograph. The Interface Region Imaging Spectrograph, (IRIS) is currently the highest spatial and spectral resolution, space based, solar spectrograph. Ongoing calibration is important to maintaining the quality of IRIS data. Using a Mercury transit against the backdrop of the dynamic solar atmosphere, I characterize the spatial point spread functions of the spectrograph with a unique, iterative, blind, deconvolution algorithm. An associated deconvolution routine improves the ability of IRIS to resolve spatially compact solar features. This technique is made freely available to the community for use with past and future IRIS observations. The Multi-Order Extreme Ultraviolet Spectrograph (MOSES) is a slitless spectrograph that collects co-temporal, but overlapping spatial and spectral images of solar spectral lines. Untangling these images presents an ill-posed inversion problem. I develop a fast, automated method that returns Doppler shifts of compact solar objects over the entire MOSES field of view with a minimum of effort and interpretation bias. The Extreme ultraviolet Snapshot Imaging Spectrograph (ESIS) is a slitless spectrograph that extends the MOSES concept. I describe this new instrument, which is far more complex and distinct as compared to MOSES, and the contributions I made in the form of optical design and optimization. ESIS will improve the quality of spatial and spectral information obtained from compact and extended solar features, and represents the next step in solar slitless spectroscopy. Taken together, these contributions advance the field by supporting existing instrumentation and by developing new instrumentation and techniques for future observations of the solar atmosphere.Item Explosive events in the quiet Sun: extreme ultraviolet imaging spectroscopy instrumentation and observations(Montana State University - Bozeman, College of Letters & Science, 2017) Rust, Thomas Ludwell; Chairperson, Graduate Committee: Charles C. KankelborgExplosive event is the name given to slit spectrograph observations of high spectroscopic velocities in solar transition region spectral lines. Explosive events show much variety that cannot yet be explained by a single theory. It is commonly believed that explosive events are powered by magnetic reconnection. The evolution of the line core appears to be an important indicator of which particular reconnection process is at work. The Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) is a novel slitless spectrograph designed for imaging spectroscopy of solar extreme ultraviolet (EUV) spectral lines. The spectrograph design forgoes a slit and images instead at three spectral orders of a concave grating. The images are formed simultaneously so the resulting spatial and spectral information is co-temporal over the 20'x10' instrument field of view. This is an advantage over slit spectrographs which build a field of view one narrow slit at a time. The cost of co-temporal imaging spectroscopy with the MOSES is increased data complexity relative to slit spectrograph data. The MOSES data must undergo tomographic inversion for recovery of line profiles. I use the unique data from the MOSES to study transition region explosive events in the He II 304 A spectral line. I identify 41 examples of explosive events which include 5 blue shifted jets, 2 red shifted jets, and 10 bi-directional jets. Typical doppler speeds are approximately 100km s-1. I show the early development of one blue jet and one bi-directional jet and find no acceleration phase at the onset of the event. The bi-directional jets are interesting because they are predicted in models of Petschek reconnection in the transition region. I develop an inversion algorithm for the MOSES data and test it on synthetic observations of a bi-directional jet. The inversion is based on a multiplicative algebraic reconstruction technique (MART). The inversion successfully reproduces synthetic line profiles. I then use the inversion to study the time evolution of a bi-directional jet. The inverted line profiles show fast doppler shifted components and no measurable line core emission. The blue and red wings of the jet show increasing spatial separation with time.Item Measurement of the variations in the reception of solar ultra-violet radiation at the earth's surface(Montana State University - Bozeman, College of Letters & Science, 1949) Kutzman, Nathaniel J.Item Coupling the photospheric and coronal magnetic fields : observations and analysis(Montana State University - Bozeman, College of Letters & Science, 1998) Handy, Brian NealItem A vacuum ultraviolet atomic beam light source(Montana State University - Bozeman, College of Letters & Science, 1969) Govertsen, Glenn Alden