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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 An empirical study of coronal observations at the solar limb(Montana State University - Bozeman, College of Letters & Science, 2016) Freed, Michael Scott; Chairperson, Graduate Committee: David E. McKenzie; Dana W. Longcope and David E. McKenzie were co-authors of the article, 'Three-year global survey of coronal null points from PFSS modeling and SDO observations' in the journal 'Solar physics' which is contained within this thesis.; David E. McKenzie, Dana W. Longcope, and Mikki Wilburn were co-authors of the article, 'Analysis of flows inside quiescent prominences as captured by hinode/solar optical telescope' in the journal 'The astrophysical journal' which is contained within this thesis.; David E. McKenzie was a co-author of the article, 'Quantifying turbulent dynamics found within the plasma sheets of multiple solar flares' submitted to the journal 'The astrophysical journal' which is contained within this thesis.Solar observations were employed in this work to quantify motion and structures seen in the sun's corona with particular attention given to features found at the solar limb. These features consist of coronal magnetic-null points, quiescent prominences, and post flare eruption plasma sheets. Extreme-ultraviolet (EUV) observations from the Solar Dynamics Observatory (SDO) spacecraft were used to determine the fidelity of the commonly used potential field source surface (PFSS) model for predicting the location of coronal magnetic-null-points. Several properties of the null points were also investigated to ascertain if they had any effect on their observability. Next, quiescent prominence observations from the Hinode/Solar Optical Telescope satellite were used to create velocity maps of the plasma found in these structures. The derived velocities provided insight into the vorticity, kinetic energy, and oscillations that reside in these prominences. Primarily, this investigation was concerned with determining the distribution of velocity and vorticity at different length scales by applying a power spectral density analysis. All of this information is intended to strengthen our understanding on how these prominences evolve and potentially become unstable. An identical analysis is then conducted on post-flare-eruption plasma sheets observed in EUV by the space based SDO and TRACE satellites. Investigating the dynamics that reside in these plasma sheets are crucial for understanding the conditions that trigger and accelerate the magnetic reconnection responsible for producing these energetic solar flares.Item Statistical properties of separators in model active regions(Montana State University - Bozeman, College of Letters & Science, 1998) Welsch, Brian ThomasItem Determining heating rates in reconnection formed flare loops(Montana State University - Bozeman, College of Letters & Science, 2014) Liu, Wenjuan; Chairperson, Graduate Committee: Jiong Qiu; Jiong Qiu, Dana W. Longcope and Amir Caspi were co-authors of the article, 'Determining heating rates in reconnection formed flare loops of the M8.0 flare on 2005 May 13' in the journal 'The astrophysical journal' which is contained within this thesis.; Jiong Qiu was a co-author of the article, 'Analyses of flare EUV emissions observed by AIA and EVE' submitted to the journal 'The astrophysical journal' which is contained within this thesis.In this work, we determine heating rates in reconnection formed are loops with analysis of observations and models. We utilize the spatially resolved ultraviolet (UV) light curves and the thick-target hard X-ray (HXR) emission to construct heating rates of a few thousand are loops anchored at the UV footpoints. These loops are formed and heated by magnetic reconnection taking place successively. These heating rates are then used as an energy input in the zero-dimensional Enthalpy-Based Thermal Evolution of Loops (EBTEL) model to calculate the evolution of plasmas in these loops and compute synthetic spectra and light curves in Soft X-ray (SXR) and extreme ultraviolet (EUV), which compare favorably with those observed by the Geostationary Operational Environmental Satellite (GOES), Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and Solar Dynamics Observatory (SDO). With a steady-state assumption, we also compute the transition-region differential emission measure (DEM) at the base of each are loop during its decay phase, and compare the predicted UV and EUV emissions at the footpoints with AIA observations. This study presents a method to constrain heating of reconnection-formed are loops using all available observations, and provides insight into the physics of energy release and plasma heating during the are. Furthermore, using RHESSI HXR observations, we could also infer the fraction of non-thermal beam heating in the total heating rate of are loops. For an M8.0 are on 2005 May 13, the lower limit of the total energy used to heat the are loops is estimated to be 1.22 x 10 31 ergs, out of which, less than 20% is carried by beam-driven upflows during the impulsive phase. The method is also applied to analyzing an eruptive M3.7 are on 2011 March 7 and a compact C3.9 are on 2012 June 17. Both flares are observed in EUV wavelengths by the Atmospheric Imaging Assembly (AIA) and Extreme Ultraviolet Variability Experiment (EVE) onboard the SDO, which allow us to investigate the are evolution from the heating to cooling phase. The results show that the model-computed synthetic EUV emissions agree very well with those observed in AIA bands or EVE lines, indicating that the method successfully captures heating events and appropriately describes mean properties of are plasma shortly after the heating phase.Item The topology of magnetic reconnection in solar flares(Montana State University - Bozeman, College of Letters & Science, 2007) Des Jardins, Angela Colman; Chairperson, Graduate Committee: Richard Canfield; Dana Longcope (co-chair)In order to better understand the location and evolution of magnetic reconnection, which is thought to be the energy release mechanism in solar flares, I combine the analysis of hard X-ray (HXR) sources observed by RHESSI with a three-dimensional, quantitative magnetic charge topology (MCT) model. I first examine the evolution of reconnection by analyzing the relationship between observed HXR footpoint motions and a topological feature called spine lines. With a high degree of confidence, I find that the HXR footpoints sources moved along the spine lines. The standard two dimensional flare model cannot explain this relationship. Therefore, I present a three dimensional model in which the movement of footpoints along spine lines can be understood. To better analyze the location of reconnection, I developed a more detailed method for representing photospheric magnetic fields in the MCT model.Item Patchy reconnection in the solar corona(Montana State University - Bozeman, College of Letters & Science, 2011) Guidoni, Silvina Esther; Chairperson, Graduate Committee: Dana W. LongcopeMagnetic reconnection in plasmas, a process characterized by a change in connectivity of field lines that are broken and connected to other ones with different topology, owes its usefulness to its ability to unify a wide range of phenomena within a single universal principle. There are newly observed phenomena in the solar corona that cannot be reconciled with two-dimensional or steady-state standard models of magnetic reconnection. Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet (magnetic discontinuity) and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-dependent, anisotropic viscosity and thermal conductivity is essential for self-consistently producing gas-dynamic shocks inside reconnected tubes that heat and compress plasma to observed temperatures and densities. The shock thickness can be as long as the entire tube and heat can be conducted along tube's legs, possibly driving chromospheric evaporation. We developed a computer program that solves numerically the thin flux tube equations that govern the retraction of reconnected tubes. Simulations carried out with this program corroborate our theoretical predictions. A comparison of these simulations with fully three-dimensional magnetohydrodynamic simulations is presented to assess the validity of the thin flux tube model. We also present an observational method based on total emission measure and mean temperature to determine where in the current sheet a tube was reconnected.Item Predictions of reconnected flux, energy and helicity in eruptive solar flares(Montana State University - Bozeman, College of Letters & Science, 2010) Kazachenko, Maria Dmitriyevna; Chairperson, Graduate Committee: Jiong Qiu; Richard Canfield (co-chair); Richard C. Canfield, Dana W. Longcope, Jiong Qiu, Angela DesJardins, and Richard W. Nightingale were co-authors of the article, 'Sunspot rotation, flare energetics and flux rope helicity: the eruptive flare on 2005 May 13' in the journal 'The astrophysical journal' which is contained within this thesis.; Richard C. Canfield, Dana W. Longcope, and Jiong Qiu were co-authors of the article, 'Sunspot rotation, flare energetics and flux rope helicity: the eruptive flare on 2003 October 28' in the journal 'The astrophysical journal' which is contained within this thesis.; Richard C. Canfield, Dana W. Longcope, and Jiong Qiu were co-authors of the article, 'Predictions of energy and helicity in four major eruptive solar flares' in the journal 'Solar Physics' which is contained within this thesis.In order to better understand the solar genesis of interplanetary magnetic clouds, I model the magnetic and topological properties of several large eruptive solar flares and relate them to observations. My main hypothesis is that the flux ropes ejected during eruptive solar flares are the result of a sequence of magnetic reconnections. To test this hypothesis, I use the three-dimensional Minimum Current Corona model of flare energy storage (Longcope, 1996) together with pre-flare photospheric magnetic field and flare ribbon observations to predict the basic flare properties: reconnected magnetic flux, free energy, and flux rope helicity. Initially, the MCC model was able to quantify the properties of the flares that occur in active regions with only photospheric shearing motions. Since rotating motions may also play a key role in the flare energetics, I develop a method for including both shearing and rotating motions into the MCC model. I use this modified method to predict the model flare properties and then compare them to the observed quantities. Firstly, for two flares in active regions with fast rotating sunspots, I find that the relative importance of shearing and rotation to those flares depends critically on their location within the parent active region topology. Secondly, for four flares analyzed with the MCC model (three flares described here and one flare described in Longcope et al. (2007)), I find that the modeled flare properties agree with the observed properties within the uncertainties of the methods used. This agreement compels me to believe that the magnetic clouds associated with these four solar flares are formed by low-corona magnetic reconnection during the eruption as modeled by the MCC model, rather than eruption of pre-existing structures in the corona or formation in the upper corona with participation of the global magnetic field. I note that since all four flares occurred in active regions without significant pre-flare flux emergence and/or cancellation, the energy and helicity values I find are due primarily to shearing and rotating motions, which are sufficient to account for the observed flare energy and MC helicity.Item Using extreme ultra-violet and soft x-ray observations as probes of magnetic reconnection during solar flares(Montana State University - Bozeman, College of Letters & Science, 2010) Savage, Sabrina Leah; Chairperson, Graduate Committee: David E. McKenzieSunward-flowing voids above post-coronal mass ejection (CME) flare arcades were first discovered using the soft X-ray telescope (SXT) aboard Yohkoh and have since been observed with TRACE (extreme ultra-violet (EUV)), SOHO/LASCO (white light), SOHO/SUMER (EUV spectra), and Hinode/XRT (soft X-rays (SXR)). These supra-arcade downflows (SADs) have been shown to be plasma deficient with respect to their surroundings and follow trajectories which slow as they reach the top of the arcade. Characteristics such as these are consistent with post-reconnection magnetic flux tube cross-sections. The tubes retract from a reconnection site high in the corona until they reach a more potential magnetic configuration - a process in line with the standard model of reconnection. Viewed from a perpendicular angle, SADs should appear as shrinking loops rather than downflowing voids. In fact, observations of supra-arcade downflowing loops (SADLs) yield speeds and decelerations consistent with those determined for SADs. For this dissertation I have compiled a substantial SADs flare catalog and have developed semi-automatic detection software to detect and track individual downflows in order to provide statistically significant samples of parameters such as velocity, acceleration, area, magnetic flux, shrinkage energy, and reconnection rate. In addition, I provide measurements connecting supra-arcade upflows with flows observed by LASCO in the outer corona following a CME which further substantiates the standard reconnection model. I discuss these measurements, how they were obtained, and what impact they have on reconnection models.