Theses and Dissertations at Montana State University (MSU)
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Item Novel models and observations of energetic events in the solar transition region(Montana State University - Bozeman, College of Letters & Science, 2021) Parker, Jacob Douglas; Chairperson, Graduate Committee: Charles C. Kankelborg; Dana Longcope was a co-author of the article, 'Modeling a propagating sawtooth flare ribbon as a tearing mode in the presence of velocity shear' in the journal 'Astrophysical journal' which is contained within this dissertation.; Charles Kankelborg was a co-author of the article, 'Determining the spectral content of MOSES images' submitted to the journal 'Astrophysical journal' which is contained within this dissertation.; Roy Smart, Charles Kankelborg, Amy Winebarger and Nelson Goldsworth were co-authors of the article, 'First flight of the EUV snapshot imaging spectrograph (ESIS)' submitted to the journal 'Astrophysical journal' which is contained within this dissertation.The solar atmosphere is an energetic and violent place capable of producing eruptions that affect us on earth. In order to better understand these events, so that we might improve out ability to model and predict them, we observe the sun from space to diagnose the local plasma conditions and track its evolution. The transition region, a thin region of the solar atmosphere separating the chromosphere from the corona, is where the solar atmosphere transitions rapidly from ten thousand, to one million kelvin and is therefore thought to play an important roll in the transfer of mass and energy to the hot corona. The sun's magnetic field, and magnetic reconnection, are thought to contribute to the increased temperature of the corona, since the cooler lower solar atmosphere cannot heat it via thermal conduction or convection. Explosive events, small solar eruptions likely driven by magnetic reconnection, are frequent in the transition region, making it an attractive area of the atmosphere to study and gather information on the processes. Using Computed Tomography Imaging Spectrographs (CTIS), capable of measuring spectral line profiles over a wide fields of view at every exposure, we find many eruptive events in the transition region to be spatially complex, three dimensional, and to evolve on rapid timescales. This demonstrates the utility of, and need to continue developing, CTIS style instruments for solar study since they provide a more complete picture of solar events, allowing us to improve our understanding of our closest star.Item Examination of coronal loops between quiescent active regions(Montana State University - Bozeman, College of Letters & Science, 2021) McCarthy, Marika Isabel; Chairperson, Graduate Committee: Dana W. Longcope; Dana W. Longcope, Anna V. Malanushenko and David E. McKenzie were co-authors of the article, 'Measuring and modeling the rate of separator reconnection between an emerging and an existing active region' in the journal 'The astrophysical journal' which is contained within this dissertation.; Dana W. Longcope and Anna V. Malanushenko were co-authors of the article, 'Multispacecraft observations of coronal loops to verify a force-free field reconstruction and infer loop cross sections' in the journal 'The astrophysical journal' which is contained within this dissertation.; Dana W. Longcope and Jada Walters were co-authors of the article, 'Temperature evolution of coronal flux observed through multiple extreme ultraviolet wavelengths' submitted to the journal ''The astrophysical journal' which is contained within this dissertation.Active regions are dynamic and constantly evolving portions of the Sun, where the magnetic field emerges from beneath the solar surface and expands into the corona. Hot, dense plasma is aligned to these field lines and these brightly emitting structures are called coronal loops. These loops are the direct manifestations of solar magnetic fields, and thus observations of them can be used to investigate the structural evolution of the corona. As an active region is believed to be a single, isolated magnetic system, any flux linkage between multiple active regions must be formed in the corona post-emergence. Direct observations of new loops can provide evidence of this when using a two-active region system as a laboratory. Loops in such a system were examined in a variety of ways. First, interconnecting loops between two active regions over a 48-hour period were cataloged, testing the assumption that all interconnecting loops are new instance of flux linkage. The flux was significantly over-counted, which could be attributed either to the modeling technique used therein or the assumed structure (e.g., cross-sectional shape) of the loops. Both of these possibilities were tested by supplementing the catalog with data from a second observational line-of-sight (LOS). The results of this study contends that some loops have non-circular cross-sections, and some might even be less structured such that they do not have enough emission along the second LOS to be observed. Another possible reason for the overcounting of flux could be attributed to a loop brightening multiple times. We test this by looking at properties of loops from the same interconnecting region, but observed in different temperatures.Item Network flux transport: concept and application to solar magnetism(Montana State University - Bozeman, College of Letters & Science, 2019) Eckberg, Jon Thomas; Chairperson, Graduate Committee: Charles C. KankelborgWe have developed a method to efficiently simulate the dynamics of the magnetic flux in the solar network. We call this method Network Flux Transport (NFT). Implemented using a Spherical Centroidal Voronoi Tessellation (SCVT) based network model, magnetic flux is advected by photospheric plasma velocity fields according to the geometry of the SCVT model. We test NFT by simulating the magnetism of the Solar poles. The poles of the sun above 55 deg latitude are free from flux emergence from active regions or ephemeral regions. As such, they are ideal targets for a simplified simulation that relies on the strengths of the NFT model. This simulation method reproduces the magnetic and spatial distributions for the solar poles over two full solar cycles.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 Long-term variability of the sun in the context of solar-analog stars(Montana State University - Bozeman, College of Letters & Science, 2017) Egeland, Ricky Alan; Chairperson, Graduate Committee: Dana W. LongcopeThe Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H & K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H & K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H & K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar S-index to be 5-9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude ~12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun's are rare in stars of approximately the solar mass, and that the proper conditions may be restricted to a relatively narrow range of rotation rates.Item Connecting coronal holes and open magnetic flux through observation and models of solar cycles 23 and 24(Montana State University - Bozeman, College of Letters & Science, 2015) Lowder, Christopher Alan; Chairperson, Graduate Committee: Jiong Qiu; Robert Leamon (co-chair); Jiong Qiu, Robert Leamon and Yang Liu were co-authors of the article, 'Coronal hole detection and open flux measurements' in the journal 'The astrophysical journal' which is contained within this thesis.; Jiong Qiu and Robert Leamon were co-authors of the article, 'Coronal holes and open flux in solar cycles 23 and 24' submitted to the journal 'The astrophysical journal' which is contained within this thesis.; Jiong Qiu, Robert Leamon and Dana Longcope were co-authors of the article, 'A flux transport model for computation of open magnetic field' submitted to the journal 'The astrophysical journal' which is contained within this thesis.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.Item Empirical studies on the initiation of impulsive heating in coronal loops(Montana State University - Bozeman, College of Letters & Science, 2014) Kobelski, Adam Robert; Chairperson, Graduate Committee: David E. McKenzie; David E. McKenzie and Martin Donachie were co-authors of the article, 'Modeling active region transient brightenings observed with XRT as multi-stranded loops' in the journal 'The astrophysical journal' which is contained within this thesis.; David E. McKenzie was a co-author of the article, 'Forward modeling transient brightenings and microflares around an active region observed with HI-C' submitted to the journal 'The astrophysical journal' which is contained within this thesis.; David E. McKenzie, Daniel B. Seaton and Derek A. Lamb were co-authors of the article, 'Initiation of AR-AR reconnection after flux emergence using PROBA2 SWAP and LYRA' submitted to the journal 'The astrophysical journal' which is contained within this thesis.; Steven H. Saar, Mark A.Weber, David E. McKenzie and Katharine K. Reeves were co-authors of the article, 'Calibrating data from the HINODE/X-ray telescope and associated uncertainties' in the journal 'Solar physics' which is contained within this thesis.The heating of the solar corona is an important topic both for scientists and modern society. One of the most fundamental of structures in the corona are bundles of plasma confined to the magnetic field, loops. Here we perform empirical studies to better understand the mechanisms responsible for heating loops. We observe loops in X-rays with XRT and model the observations as bundles of independent strands, showing that the mechanisms instigating the heating of loops is likely impulsive, yet requires multiple heating events to match observations. We also observe and model very small loops with Hi-C, exploiting the high resolution to show that the frequency with which small loops are heated is larger than expected. This study also puts constraints on the size of the heating events. We also perform a study on the initiation of magnetic reconnection between neighboring active regions, in hopes of understanding how magnetic fields interact, evolve and heat coronal loops. We close with a discussion on calibrating the data from a solar X-ray telescope and interpret the uncertainties within.Item Multi-instrument observations of coronal loops(Montana State University - Bozeman, College of Letters & Science, 2012) Scott, Jason Terrence; Chairperson, Graduate Committee: Petrus MartensThis document exhibits results of analysis from data collected with multiple EUV satellites (SOHO, TRACE, STEREO, Hinode, and SDO). The focus is the detailed observation of coronal loops using multiple instruments, i.e. filter imagers and spectrometers. Techniques for comparing the different instruments and deriving loop parameters are demonstrated. Attention is given to the effects the different instruments may introduce into the data and their interpretation. The assembled loop parameters are compared to basic energy balance equations and scaling laws. Discussion of the blue-shifted, asymmetric, and line broadened spectral line profiles near the footpoints of coronal loops is made. The first quantitative analysis of the anti-correlation between intensity and spectral line broadening for isolated regions along loops and their footpoints is presented. A magnetic model of an active region shows where the separatrices meet the photospheric boundary. At the boundary, the spectral data reveal concentrated regions of increased blue-shifted outflows, blue wing asymmetry, and line broadening. This is found just outside the footpoints of bright loops. The intensity and line broadening in this region are anti-correlated. A comparison of the similarities in the spectroscopic structure near the footpoints of the arcade loops and more isolated loops suggests the notion of consistent structuring for the bright loops forming an apparent edge of an active region core.Item Towards better constrained models of the solar magnetic cycle(Montana State University - Bozeman, College of Letters & Science, 2010) Munoz-Jaramillo, Andres; Chairperson, Graduate Committee: Petrus MartensThe best tools we have for understanding the origin of solar magnetic variability are kinematic dynamo models. During the last decade, this type of models has seen a continuous evolution and has become increasingly successful at reproducing solar cycle characteristics. The basic ingredients of these models are: the solar differential rotation - which acts as the main source of energy for the system by shearing the magnetic field; the meridional circulation - which plays a crucial role in magnetic field transport; the turbulent diffusivity - which attempts to capture the effect of convective turbulence on the large scale magnetic field; and the poloidal field source - which closes the cycle by regenerating the poloidal magnetic field. However, most of these ingredients remain poorly constrained which allows one to obtain solar-like solutions by "tuning" the input parameters, leading to controversy regarding which parameter set is more appropriate. In this thesis we revisit each of those ingredients in an attempt to constrain them better by using observational data and theoretical considerations, reducing the amount of free parameters in the model. For the meridional flow and differential rotation we use helioseismic data to constrain free parameters and find that the differential rotation is well determined, but the available data can only constrain the latitudinal dependence of the meridional flow. For the turbulent magnetic diffusivity we show that combining mixing-length theory estimates with magnetic quenching allows us to obtain viable magnetic cycles and that the commonly used diffusivity profiles can be understood as a spatiotemporal average of this process. For the poloidal source we introduce a more realistic way of modeling active region emergence and decay and find that this resolves existing discrepancies between kinematic dynamo models and surface flux transport simulations. We also study the physical mechanisms behind the unusually long minimum of cycle 23 and find it to be tied to changes in the meridional flow. Finally, by carefully constraining the system through surface magnetic field observations, we find that what is believed to be the primary source of poloidal field (also known as Babckock-Leigthon mechanism) may not be enough to sustain the solar magnetic cycle.