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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 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 Modeling and understanding coronal loop dynamics during solar flares(Montana State University - Bozeman, College of Letters & Science, 2020) Unverferth, John Edward, IV; Chairperson, Graduate Committee: Dana W. Longcope; Dana Longcope was a co-author of the article, 'Effects of the canopy and flux tube anchoring on evaporation flow of a solar flare' in the journal 'The astrophysical journal' which is contained within this dissertation.; Dana Longcope was a co-author of the article, 'Modeling observable differences in flare loop evolution due to reconnection location and current sheet structure' in the journal 'The astrophysical journal' which is contained within this dissertation.; Dana Longcope was a co-author of the article, 'Flux tube interactions as a cause for sub-alfvenic reconnection outflow' submitted to the journal 'The astrophysical journal' which is contained within this dissertation.Magnetic reconnection is widely considered to be the mechanism behind solar flares. Models powered by reconnection manage to explain many of the observational features seen in a flare. However, these models miss or contradict important elements of the flare. Here we consider three effects overlooked by models. First, the role played by the magnetic canopy in determining the chromospheric response in a flare. Second, how variations in magnetic field strength along the current sheet impact the evolution of are loops. Third, how flux tube interactions with the current sheet can lead to sub-Alfvenic motion, bringing dynamics in line with observations. These three effects were investigated with the use of one dimensional and thin flux tube models. This allowed for the dynamics to be considered independent of the reconnection process that generated the flux tubes. The canopy interaction revealed that the creation of an expansion followed by a constriction, a chamber in the flux tube, leads to multiple solutions. The solutions include smooth flow and standing shocks in the chamber. The standing shock increases the emission of the flow, as well as slowing it to subsonic speeds. The shocked solution shifts the ensemble of flux tubes to have a distribution that would indicate slower speeds than expected. The structure of the current sheet magnetic field leaves a signature on the flux tube. Each case leads to a difference in emission. Retraction through a constricting field creating a plug of material leading to a bright emission in the apex. This contrasts with retraction through an expanding field which generates high temperatures, but as a fainter emission. The interaction of drag in the current sheet allowed for the retraction to proceed at slower rates. The slower retraction matches observations of features in flares more accurately. The slower retraction also increases the brightness of the synthetic current sheet. This increased brightness brings the current sheet closer to the observed brightness. These investigations found that there was benefit to considering these additional effects. Each one of these effects was found to bring the models more in line to what observations note.Item Observations and modeling of plasma flows driven by solar flares(Montana State University - Bozeman, College of Letters & Science, 2016) Brannon, Sean Robert; Chairperson, Graduate Committee: Dana W. Longcope; Dana Longcope was a co-author of the article, 'Modeling properties of chromospheric evaporation driven by thermal conduction fronts from reconnection shocks' in the journal 'The astrophysical journal' which is contained within this thesis.; Dana W. Longcope and Jiong Qiu were co-authors of the article, 'Spectroscopic observations of evolving flare ribbon substructure suggesting origin in current sheet waves' in the journal 'The astrophysical journal' which is contained within this thesis.One of the fundamental statements that can be made about the solar atmosphere is that it is structured. This structuring is generally believed to be the result of both the arrangement of the magnetic field in the corona and the distribution of plasma along magnetic loops. The standard model of solar flares involves plasma transported into coronal loops via a process known as chromospheric evaporation, and the resulting evolution of the are loops is believed to be sensitive to the physical mechanism of energy input into the chromosphere by the are. We present here the results of three investigations into chromospheric plasma flows driven by solar are energy release and transport. First, we develop a 1-D hydrodynamic code to simulate the response of a simplified model chromosphere to energy input via thermal conduction from reconnection-driven shocks. We use the results from a set of simulations spanning a parameter space in both shock speed and chromospheric-to-coronal temperature ratio to infer power-law relationships between these quantities and observable evaporation properties. Second, we use imaging and spectral observations of a quasi-periodic oscillation of a are ribbon to determine the phase relationship between Doppler shifts of the ribbon plasma and the oscillation. The phase difference we find leads us to suggest an origin in a current sheet instability. Finally, we use imaging and spectral data of an on-disk are event and resulting are loop plasma flows to generally validate the standard picture of are loop evolution, including evaporation, cooling time, and draining downflows, and we use a simple free-fall model to produce the first direct comparison between observed and synthetic downflow spectra.Item Analytical and numerical modeling of coronal supra-arcade fan structures(Montana State University - Bozeman, College of Letters & Science, 2016) Scott, Roger Benezet; Chairperson, Graduate Committee: David E. McKenzie; Dana W. Longcope and David E. McKenzie were co-authors of the article, 'Peristaltic pumping near post-CME supra-arcade current sheets' in the journal 'The astrophysical journal' which is contained within this thesis.; Dana W. Longcope and David E. McKenzie were co-authors of the article, 'Numerical simulations of plasma dynamics in the vicinity of a retracting flux tube' submitted to the journal 'The astrophysical journal' which is contained within this thesis.; David E. McKenzie and Dana W. Longcope were co-authors of the article, 'Inferring the magnetohydrodynamic structure of solar flare supra-arcade plasmas from a data assimilated field transport model' submitted to the journal 'The astrophysical journal' which is contained within this thesis.Among the myriad of interesting phenomenon in the solar corona is the highly dynamic region above active region arcades, commonly referred to as the "supra-arcade" region. In the minutes and hours following the formation of an arcade of post-flare loops, we commonly observe the development of a curtain like structure, with spiny rays of enhanced emission in X-Ray and extreme ultra-violet. Additionally, these structures often exhibit dynamics over a variety of length scales, from large-amplitude coherent transverse oscillations, to the appearance of low-emission columns that seem to descend toward the solar limb. The wealth of dynamical aspects that are present in the supra-arcade seems to indicate that the plasma there is subject to a complex balance of influencing factors, which makes it difficult to develop a self-consistent hypothesis for describing all of the various features simultaneously. In this work we undertake to explain one such behavior as an isolated phenomenon. We argue that the descending low-emission voids, sometimes called Supra-Arcade Downflows (SADs) are consistent with the formation of a particular kind of shock in the vicinity of a retracting element of reconnected magnetic flux. We then use numerical simulations to expand this result to a broader parameter space, as well as investigating the details of a variety of other behavioral regimes. Finally, in an effort to understand the broader dynamics of the supra-arcade region, we undertake a study that incorporates imaging data into a numerical simulation, which can then be used to estimate the ambient plasma parameters in the supra-arcade region. In this way we show that the balance of influencing factors in the supra-arcade is indeed highly dynamic and that the simplifications offered in certain extremes of magnetohydrodynamics are ill-applied in this case.Item X-ray astrophysics of compact objects(Montana State University - Bozeman, College of Letters & Science, 2000) LeRoux, Anna Marishka KrickovichItem 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 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 Combining hydrodynamic modeling with nonthermal test particle tracking to improve flare simulations(Montana State University - Bozeman, College of Letters & Science, 2009) Winter, Henry deGraffenried, III; Chairperson, Graduate Committee: Petrus MartensSolar flares remain a subject of intense study in the solar physics community. These huge releases of energy on the Sun have direct consequences for humans on Earth and in space. The processes that impart tremendous amounts of energy are not well understood. In order to test theoretical models of flare formation and evolution, state of the art, numerical codes must be created that can accurately simulate the wide range of electromagnetic radiation emitted by flares. A direct comparison of simulated radiation to increasingly detailed observations will allow scientists to test the validity of theoretical models. To accomplish this task, numerical codes were developed that can simulate both the thermal and nonthermal components of a flaring plasma, their interactions, and their emissions. The HYLOOP code combines a hydrodynamic equation solver with a nonthermal particle tracking code in order to simulate the thermal and nonthermal aspects of a flare. A solar flare was simulated using this new code with a static atmosphere and with a dynamic atmosphere, to illustrate the importance of considering hydrodynamic effects on nonthermal beam evolution. The importance of density gradients in the evolution of nonthermal electron beams was investigated by studying their effects in isolation. The importance of the initial pitch-angle cosine distribution to flare dynamics was investigated. Emission in XRT filters were calculated and analyzed to see if there were soft X-ray signatures that could give clues to the nonthermal particle distributions. Finally the HXR source motions that appeared in the simulations were compared to real observations of this phenomena.