• Characteristic behavior of the dayside aurora in the minutes leading up to substorm onset: evidence for external triggering of substorms by the interplanetary magnetic field

      Andersen, Carl Stephen (2005-12)
      Two meridian scanning photometers, one located in Alaska and one in Svalbard, are used to examine the behavior of the dayside aurora just before the onset of the expansion phase of 61 substorms. In a strong majority of cases (80%), a poleward movement of the dayside aurora is seen in the minutes preceding sub storm onset. For the cases examined where a poleward movement of the dayside aurora is seen, a northward turning of the (generally southward) IMF is usually, but not always, seen. This suggests that for a majority of substorms, the 'trigger' is, or is related to, a northward turning of the IMF which can be seen by the motions of the dayside aurora. The observed movements of the dayside aurora and supposed onset triggers begin, on average, 12 minutes before substorm onset, which is the period before on-set during which nightside 'auroral fading' is known to happen. Two opposite but not necessarily exclusive behaviors of ionospheric convection have also been reported to occur during this period before onset, namely a decrease and/or an increase in polar cap convection velocities. Radar measurements of ionospheric convection are examined for these events but do not show an easily identifiable characteristic behavior.
    • Characteristics of dayside auroral displays in relation to magnetospheric processes

      Minow, Joseph I.; Smith, Roger W. (1997)
      The use of dayside aurorae as a ground based monitor of magnetopause activity is explored in this thesis. The origin of diffuse (OI) 630.0 nm emissions in the midday auroral oval is considered first. Analysis of low altitude satellite records of precipitating charged particles within the cusp show an unstructured electron component that will produce a 0.5-1 kR 630.0 nm emission throughout the cusp. Distribution of the electrons is controlled by the requirement of charge neutrality in the cusp, predicting a diffuse 630.0 nm background even if the magnetosheath plasma is introduced into the magnetosphere in discrete merging events. Cusp electron fluxes also contain a structured component characterized by enhancements in the electron energy and energy flux over background values in narrow regions a few 10's of kilometers in width. These structured features are identified as the source of the transient midday arcs. An auroral model is developed to study the morphology of (OI) 630.0 nm auroral emissions produced by the transient arcs. The model demonstrates that a diffuse 630.0 nm background emission is produced by transient arcs due to the long lifetime of the O$(\sp1D)$ state. Two sources of diffuse 630.0 nm background emissions exist in the cusp which may originate in discrete merging events. The conclusion is that persistent 630.0 nm emissions cannot be interpreted as prima facie evidence for continuous particle transport from the magnetosheath across the magnetopause boundary and into the polar cusp. The second subject that is considered is the analysis of temporal and spatial variations of the diffuse 557.7 nm pulsating aurora in relation to the 630.0 nm dominated transient aurora. Temporal variations at the poleward boundary of the diffuse 557.7 nm aurora correlate with the formation of the 630.0 nm transient aurorae suggesting that the two events are related. The character of the auroral variations is consistent with the behavior of particle populations reported during satellite observations of flux transfer events near the dayside magnetopause. An interpretation of the events in terms of impulsive magnetic reconnection yields a new observation that relates the poleward moving transient auroral arcs in the midday sector to the flux transfer events.
    • Characterization and diagnostic methods for geomagnetic auroral infrasound waves

      Oldham, Justin J.; Szuberla, Curt A. (2015-12)
      Infrasonic perturbations resulting from auroral activity have been observed since the 1950's. In the last decade advances in infrasonic microphone sensitivity, high latitude sensor coverage, time series analysis methods and computational efficiency have elucidated new types of auroral infrasound. Persistent periods of infrasonic activity associated with geomagnetic sub-storms have been termed geomagnetic auroral infrasound waves [GAIW]. We consider 63 GAIW events recorded by the Fairbanks, AK infrasonic array I53US ranging from 2003 to 2014 and encompassing a complete solar cycle. We make observations of the acoustic features of these events alongside magnetometer, riometer, and all-sky camera data in an effort to quantify the ionospheric conditions suitable for infrasound generation. We find that, on average, the generation mechanism for GAIW is confined to a region centered about ~60° longitude east of the anti-Sun-Earth line and at ~77° North latitude. We note furthermore that in all cases considered wherein imaging riometer data are available, that dynamic regions of heightened ionospheric conductivity periodically cross the overhead zenith. Consistent features in concurrent magnetometer conditions are also noted, with irregular oscillations in the horizontal component of the field ubiquitous in all cases. In an effort to produce ionosphere based infrasound free from the clutter and unknowns typical of geophysical observations, an experiment was undertaken at the High Frequency Active Auroral Research Program [HAARP] facility in 2012. Infrasonic signals appearing to originate from a source region overhead were observed briefly on 9 August 2012. The signals were observed during a period when an electrojet current was presumed to have passed overhead and while the facilities radio transmitter was periodically heating the lower ionosphere. Our results suggest dynamic auroral electrojet currents as primary sources of much of the observed infrasound, with modulation of the electrojets due to energetic particle precipitation, dispersion due to coupling with gravity waves, and reflection and refraction effects in the intervening atmosphere all potential factors in the shaping of the waveforms observed.
    • Cloud condensation nuclei

      Ji, Qiang; Shaw, Glenn E.; Stamnes, Knut; Bowling, Sue Ann; Benner, Richard; Kienle, Juergen; Watkins, Brenton (1995)
      In this study the supersaturation spectra of Cloud Condensation Nuclei (CCN) and the size distribution spectra of aerosols were investigated. These studies were conducted because it is believed that atmospheric aerosols, especially CCN, can affect the climate of the Earth. First, the size distributions of aerosols and the number concentrations of CCN were measured at different times in different meteorological airmass systems. The results indicate that the CCN supersaturation spectrum can be calculated from the size distribution of aerosols in only a few cases, suggesting that the direct measurement of CCN is of importance. Second, based on the measurements, a new general equation is proposed to describe the CCN supersaturation spectrum for some types of aerosols. The corresponding equation for CCN size distribution is derived. It is also shown theoretically that, with certain assumptions, the aerosol size distribution in the accumulation mode can be described by a bell-shaped distribution, in agreement with our measurements. The new equations are compared with actual data. Finally, a new method is devised to facilitate the measurement of CCN. The new instrument, which we call the "CCN Remover", separates CCN from the rest of aerosols by activation and removal. Together with a particle sizer, a new CCN measurement system, the CCN Remover Spectrometer, can provide information on both the supersaturation spectrum and the size distribution of CCN. Preliminary laboratory tests show close agreement between measurement results and theoretical predictions. The Remover Spectrometer was successfully tested in the NASA SCAR-B (Smoke, Clouds, and Radiation-Brazil) biomass burning experiment.
    • Cold ions of ionospheric origin observed at the dayside magnetopause and their effects on magnetic reconnection

      Lee, Sun-Hee; 이, 선희; Zhang, Hui; Ng, Chung-Sang; Otto, Antonius; Zong, Qiu-Gang (2015-08)
      Magnetic reconnection at the dayside magnetopause is one of the most important mechanisms that efficiently transfers solar wind particles, momentum, and energy into the magnetosphere. Magnetic reconnection at the magnetopause is usually asymmetric since the plasma and magnetic field properties are quite different in the magnetosphere and the magnetosheath. Cold dense plasma, originating either directly from the ionosphere or from the plasmasphere, has often been observed at the adjacent magnetopause. These cold plasmas may affect reconnection since they modify the plasma properties on the magnetospheric side significantly. This dissertation presents case and statistical studies of the characteristics of the cold ions observed at the dayside magnetopause by using Cluster spacecraft datasets. The plasmaspheric plumes have been distinguished from the ionospheric outows using ion pitch angle distributions. The ionospheric outows feature unidirectional or bidirectional field-aligned pitch angle distributions, whereas the plasmaspheric plumes are characterized by 90° pitch angle distributions. The occurrence rates of the plasmaspheric plumes and ionospheric outows and their dependence on the solar wind/Interplanetary Magnetic Field (IMF) conditions have been investigated. It is found that the occurrence rate of plasmaspheric plume or ionospheric plasma strongly depends on the solar wind/IMF conditions. In particular, plasmaspheric plumes tend to occur during southward IMF while ionospheric outows tends to occur during northward IMF. The occurrence rate of the plasmaspheric plumes is significantly higher on the duskside than that on the dawnside, indicating that the plasmaspheric plumes may lead to a dawn-dusk asymmetry of dayside reconnection. Furthermore, this dissertation investigates the behavior of the cold dense plasma of ionospheric origin during magnetic reconnection at the dayside magnetopause. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection near the subsolar magnetopause, the colder ions are simply entrained by E x B drift at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play a very limited role in magnetic reconnection process. Finally, this dissertation examines a controlling factor that leads to the asymmetric reconnection geometry at the magnetopause. It is demonstrated that the separatrix and ow boundary angles are greater on the magnetosheath side than on the magnetospheric side of the magnetopause, probably due to the stronger density asymmetry rather than magnetic field asymmetry at this boundary.
    • Deactivation and excitation of 0I(6s ⁵S) at above-thermal energies

      Enzweiler, Joseph A. (1982-05)
      Absolute collisional deactivation and excitation cross sections have been measured for a beam of O (⁵P-⁵S°) incident on N₂. The beam energy was varied from 3.95 to 10.65 keV. Cross sections for charge transfer (electron capture) of 0⁺ in N₂ were also measured in the energy range from 2.4 to 24.3 keV. The variation of light intensity 5436 Å (from the 6s-3p transition of the quintet system of atomic oxygen) emitted from the beam as a function of N₂ target pressure was fitted to a beam of kinetic equation to determine deactivation and excitation cross sections. The cross section for deactivation in N₂ decreases from 6.84 x 10⁻¹⁵ cm² at 3.95 keV to 1.5 x 10⁻¹⁵ cm² at 19.65 keV. The cross section for excitation decreases from 3.3 x 10⁻¹⁹ at 3.95 keV to 2.25 x 10⁻¹⁹ cm² at 19.65 keV.
    • Dependence of the ionospheric convection pattern on the conductivity and the southward IMF

      Shue, Jih-Hong; Kan, J. R.; Akasofu, S.-I.; Biswas, N. N.; Rees, M. H.; Weimer, D. R. (1993)
      Electric field measurements from the DE-2 satellite were used to determine the location of the convection reversal boundary and the potential around this boundary under a combination of interplanetary magnetic field (IMF) and auroral electrojet conditions. The electric potential is obtained by the integration of the electric fields. The convection reversal boundary is defined in this study as where the potential has its absolute maximum and minimum values. The data were sorted into 18 categories according to two levels of the negative IMF $B\sb{z},$ three ranges of IMF $B\sb{y},$ and two substorm phases. The data were fit with both continuous and discontinuous boundaries to get a functional representation of boundary potentials and locations. A simple model is constructed by solving the Laplace's equation in order to illustrate the obtained boundary potentials and locations. The results show that the enhanced electric field in the midnight sector is associated with an intense westward electrojet current. It can also be seen that the convection reversal boundary is found to be discontinuous near midnight. The discontinuous convection reversal boundary on the dayside is related to the merging near dayside cusp region. The discontinuous convection reversal boundary on the nightside is related to the conductivity enhancement. The intrusion of the dawn cell into the dusk cell is due to nonuniformity of the Hall conductivity in the ionosphere. Another model is constructed by solving the current continuity equation with field-aligned current and nonuniform conductivity added. It can be found that a secondary convection reversal, which is detached from the dusk-cell convection reversal, appears in the evening-midnight sector within the polar cap when the IMF $B\sb{y}$ is positive and the conductivity is nonuniform. This convection reversal is attributed to be created by the B $\times$ V dynamo. Also, the inclusion of the region 2 field-aligned current leads to an enhancement of the electric field in the region between the region 1 and region 2 currents.
    • Effects of gravity waves on the polar oxygen and hydroxyl airglow

      Viereck, Rodney Allen; Deehr, Charles S.; Degen, V.; Fritts, D. C.; Rees, M. H.; Smith, R. W. (1988)
      The effect of gravity waves on the OH (87 km) and O$\sb2$ (95 km) airglow emissions was examined using spectroscopic airglow data. The data was obtained from Longyearbyen, Svalbard (78$\sp\circ$N) and Fairbanks, Alaska (64$\sp\circ$N) using Ebert-Fastie spectrometers and a system of Meridian Scanning Photometers. The spectrometers scanned in wavelength from 8200A to 8750A which included the airglow emissions from the OH(6-2) Meinel band and the O$\sb2$(0-1) atmospheric band. The analysis was done by fitting a synthetic spectrum to the data and thereby the rotational temperature was calculated as well as the band intensity of each of the emissions. The rotational temperatures were assumed to represent the temperature of the emission region. Gravity waves were assumed to modify the density and temperature of the atmosphere in the region of the airglow emissions. These modifications were measured as fluctuations in the band intensity and rotational temperatures of the two emissions. In order to compare the data with theoretical models, it was necessary to calculate two parameters. The parameter $\eta$ is defined as the ratio of the amplitudes of the fluctuations in intensity and temperature. The other parameter is the phase angle between the fluctuations in intensity and temperature. These parameters were found to vary with wave period. The variations in $\eta$ and phase agreed fairly well, for long period waves, with the most recent models. None of the models agree with the observed values of $\eta$ and phase for short period waves. The second part of this thesis examines the vertical and horizontal wavelengths, the phase speeds, and the propagation directions of several specific gravity wave examples. During a 60 hour period of data taken from Svalbard, three well defined gravity waves were observed. The propagation directions implied a moving source south of the observing station.
    • Electron transport and optical emissions in the aurora

      Lummerzheim, Dirk; Rees, M. H.; Lee, L. C.; Olson, J. V.; Royer, T. C.; Stamnes, K. (1987)
      A one-dimensional, steady state auroral model is developed based on a linear electron transport calculation. A set of cross sections for electron neutral collisions describing elastic scattering, energy loss, and photon emission is compiled and used in conjunction with a discrete ordinate transport code. Calculated electron intensities are compared with in situ rocket measurements. Auroral optical emissions that result from direct electron impact on neutrals are calculated for synthetic and observed electron spectra. A systematic dependence of the brightness of auroral features on energy flux, characteristic energy, and atmospheric composition is found and parameterized. A method for interpreting the brightness and the ratio of brightnesses of certain auroral emissions in terms of the energy flux, characteristic energy, and relative oxygen density is described. Application of this method to auroral images acquired by nadir viewing instruments aboard a satellite is discussed and the distribution of energy flux, characteristic energy, and ionospheric conductances over the auroral oval is determined. Emissions that are suitable for analysing auroral spectra in terms of the atomic oxygen abundance in the auroral zone are identified.
    • Electrostatic ion cyclotron waves in barium injection experiments in space

      Kangas, Kim A.; Swift, D. W.; Stenbaek-Nielsen, H. C.; Kan, J. R. (1989-05)
      Electrostatic ion cyclotron waves are investigated in a charge-generated barium-shaped plasma directed parallel to the earth’s magnetic field. The barium plasma is generated as a result of a barium shape charge release in the upper F₂ region of the ionosphere undergoing photoionization, Using a differential velocity distribution given by Stenbaek-Nielsen et al., [1984], this situation has been modeled based on the condition of collisionless plasma. The instabilities were studied for cases with and without an ambient oxygen ion background. It was concluded that fast ionization in excess of photoionization due to the excitation of electrons by electrostatic ion cyclotron waves was not feasible for the ejection directed along the earth’s magnetic field nor would there be any contribution to Alfven’s critical velocity mechanism if the injection was directed perpendicular to the magnetic field.
    • Equilibrium structure and dynamics of near-earth plasma sheet during magnetospheric substorms

      Zhang, Lin; Otto, Antonius; Sentman, Davis; Smith, Roger; Watkins, Brenton (1997)
      A magnetofrictional method and MHD simulation are used to study MHD equilibria and dynamic evolution of the Earth's magnetosphere during a substorm growth phase. I suggest that the new "entropy anti-diffusion instability" associated with plasma transport across field lines leads to an enhanced entropy gradient and accelerates the formation of a thin current sheet during the final substorm growth phase. Based upon the MHD simulations with a pressure diffusion term, I confirm that entropy anti-diffusion instability can lead to a very thin current sheet with $B\sb{z} < 0.5nT$ and thickness $<$1000km in the near-earth magnetotail ($x \sim -8$ to $-20R\sb{e}$) during the growth phase of substorm. The formation of the thin current sheet can explain the observed explosive growth phase of substorms. In the study of magnetotail equilibrium configurations, it is found that the profile of the magnetic field strength B$\sb{z}$ component in the equatorial plane is mainly determined by the entropy $S(A)\ (S = pV\sp\gamma)$ on magnetic flux tubes. I obtain self-consistent equilibria of the Earth's magnetosphere with very strong lobe fields and a monotonically increasing $B\sb{z}$ component towards the Earth. It is also confirmed that an enhancement of the lobe flux favors the formation of a current sheet during the early substorm growth phase. However, my results do not support the notion that a critical amount of the lobe flux is required for a collapse of the tail current sheet.
    • Excitation of the ionized nitrogen molecule in the aurora

      Nielsen, Kim (2002-12)
      An understanding of the excitation mechanism of the ionospheric molecules during auroral activity is of vital importance for the overall ionospheric understanding including its interaction with the magnetosphere. In this thesis we study two emissions originating from the excited nitrogen molecule ion. The first negative (0,1) emission at 4278 Å originating from the B state, and Meinel (2,0) emission at 7852 Å originating from the A state during moderate to strong aurora have been observed with an imaging spectrograph at Poker Flat, Alaska. The B state has a short lifetime compared to the inverse collision frequency at auroral altitudes, while the A state can be deactivated during collisions at altitudes near 95 km. The B state can be populated by an up-welling of N₂ into sunlit regions. Both processes are expected to depend on auroral activity. If none of the processes are present we expect a constant ratio between the two emissions. Data for three nights have been studied and a constant ratio was found at all times. Thus neither deactivation of the A state or up-welling of the ion seem to appear during the observations presented here. The values of the ratio for the three nights are 2.53 plus-minus 0.38, 3.05 plus minus 0.22, and 3.40 plus minus 1.10, respectively.
    • Exploring the mechanisms behind nondiffusive transport in a simple turbulence model

      Ogata, Douglas; Newman, David; Sánchez, Raul; Wackerbauer, Renate; Ng, Chung-Sang (2017-05)
      Elements for nondiffusive transport have been identified in a plasma turbulence model based on the slab drift-wave model. Motivated by the self-organized criticality paradigm, a standard set of drift-wave equations in doubly-periodic spatial domain has been elevated to include a flux-driven background profile with critical gradients. The profile is maintained by the turbulence induced flux from the source to the sink. Tracers that follow the Lagrangian trajectories are the primary transport characterization technique. The competition between down-gradient relaxations and self-generated flows highlights the dual reactions to local steepening of profile gradients, which leads to different transport regimes. An additional external sheared flow further inhibits down-gradient transfer and acts as another critical threshold condition that can lead to flow-driven instabilities. Superdiffusive transport is observed primarily when radial relaxation events dominate while subdiffusive character become more prominent with self-generated and external poloidal flows. Diffusive transport exists when the superdiffusive and subdiffusive components are in balance. The interplay between turbulent relaxation and self-generated sheared poloidal flows, that form the basis for the transport explored in this model, is absent unless a flux-driven setup is used. Most of the rich dynamics were not present when running the simplified model without an equation for background profile evolution. Nondiffusive transport characteristics can also be recovered from a passive scalar field that is advected by the turbulent flow with an inherent diffusivity. The spread of a highly localized cloud of tracers and a passive scalar field reasserts the equivalence between the Lagrangian and quasi-Lagrangian frames. The coincidence between the passive scalar field with the tracers provide a regime of validity where existing experimental technique can be used to characterize transport from two-dimensional experimental data. The results from this work highlight the key features of flux-driven turbulent transport leading to nondiffusive transport. Specifcally, the dual reactions to the local steepening of profile gradients exposes the multiscale feature of turbulent transport that becomes more apparent under a flux-driven profile. The quantification of nondiffusive transport characteristics from the evolution of a passive scalar can have important implication towards the fundamental understanding of fluid turbulence and turbulent transport.
    • Formation of solar prominences and eruption of solar magnetic arcade systems

      Choe, Gwang-Son; Lee, Lou-Chuang; Akasofu, Syun-Ichi; Roederer, Juan G.; Swift, Daniel W.; Watkins, Brenton J. (1995)
      Formation and eruption of solar prominences, coronal mass ejections (CMEs) and solar flares are the most magnificent phenomena among solar activities. Observations show that there is an interrelationship among these events and that their manifestation is conditioned by certain common photospheric signatures. One of them is the increase in magnetic shear. In this thesis, the evolution of the solar atmosphere is studied by numerical simulations with photospheric motions as boundary conditions. Firstly, mechanisms of prominence formation are investigated. It is found that prominences can be formed by the development of a thermal instability (1) in a rapidly expanding magnetic arcade, (2) in a magnetic island created by magnetic reconnection or (3) in the current sheet between two bipolar arcades. Secondly, the quasi-static evolution of a magnetic arcade subject to footpoint shearing is studied under the ideal MHD condition. Three distinct evolutionary phases are found, in the last of which a current layer develops and grows indefinitely with the increasing shear. Force-free field solutions are also constructed and compared with dynamic solutions. Finally, resistive evolutions of magnetic arcades are investigated imposing resistivity on the pre-sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnection can take place to create a magnetic island. The effects of different values and spatial patterns of resistivity are studied. With a localized resistivity, most of principal features in solar eruptive processes are reproduced. A comparative study is made between the numerical results and observations.
    • High frequency backscatter from the polar and auroral e-region ionosphere

      Forsythe, Victoriya V.; Bristow, William; Conde, Mark; Sahr, John; Zhang, Hui (2017-05)
      The Earth's ionosphere contains collisional and partially-ionized plasma. The electric field, produced by the interaction between the Earth's magnetosphere and the solar wind, drives the plasma bulk motion, also known as convection, in the F-region of the ionosphere. It can also destabilize the plasma in the E-region, producing irregularities or waves. Intermediatescale waves with wavelengths of hundreds of meters can cause scintillation and fading of the Global Navigation Satellite System (GNSS) signals, whereas the small-scale waves (< 100 m) can scatter radar signals, making possible detection of these plasma structures and measurements of their characteristics such as their phase velocity and intensity. In this work, production of the decameter-scale (10 m) irregularities in the ionospheric E-region (100-120 km in altitude) at high latitudes is investigated both theoretically, using linear fluid theory of plasma instability processes that generate small-scale plasma waves, and experimentally, by analyzing data collected with the newly-deployed high-southern-latitude radars within the Super Dual Auroral Radar Network (SuperDARN). The theoretical part of this work focuses on symmetry properties of the general dispersion relation that describes wave propagation in the collisional plasma in the two-stream and gradient-drift instability regimes. The instability growth rate and phase velocity are examined under the presence of a background parallel electric field, whose influence is demonstrated to break the spatial symmetry of the wave propagation patterns. In the observational part of this thesis, a novel dual radar setup is used to examine E-region irregularities in the magnetic polar cap by probing the E-region along the same line from opposite directions. The phase velocity analysis together with raytracing simulations demonstrated that, in the polar cap, the radar backscatter is primarily controlled by the plasma density conditions. In particular, when the E-region layer is strong and stratified, the radar backscatter properties are controlled by the convection velocity, whereas for a tilted E-layer, the height and aspect angle conditions are more important. Finally, the fundamental dependence of the E-region irregularity phase velocity on the component of the plasma convection is investigated using two new SuperDARN radars at high southern latitudes where plasma convection estimates are accurately deduced from all SuperDARN radars in the southern hemisphere. Statistical analysis is presented showing that the predominance of the E-region echoes of a particular polarity is strongly dictated by the orientation of the convection plasma ow which itself has a significant asymmetry towards westward zonal flow.
    • Hot flow anomalies at earth's bow shock and their magnetospheric-ionospheric signatures

      Chu, Christina Seiman; Zhang, Hui; Otto, Antonius; Ng, Chung-Sang; Sibeck, David (2017-08)
      Hot flow anomalies (HFAs) are typically observed upstream of bow shocks. They are characterized by a significant increase in particle temperature and substantial flow deflection from the solar wind flow direction coinciding with a decrease in density. HFAs are important to study and understand because they may play an important role in solar wind-magnetosphere coupling. They may drive magnetopause motion, boundary waves, and flux transfer events. They can excite ultra low frequency waves in the magnetosphere, drive magnetic impulse events in the ionosphere, and trigger aurora brightening or dimming. Studying HFAs will aid in the understanding of fundamental processes that operate throughout the heliosphere such as particle energization and shocks. This dissertation presents statistical and case studies of hot flow anomalies identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007-2009. The characteristics and occurrence of HFAs, their dependence on solar wind/interplanetary magnetic field (IMF) conditions and location, and their magnetospheric-ionospheric signatures, have been investigated using in-situ spacecraft observations and ground based observations. THEMIS observations show that HFAs span a wide range of magnetic local times (MLTs) from approximately 7 to 16.5 MLT. HFAs were observed up to 6.3 Earth radii (RE) upstream from the bow shock. It has been found that the HFA occurrence rate depends on solar wind and interplanetary magnetic field (IMF) conditions as well as distance from the bow shock. HFA occurrence decreases with distance upstream from the bow shock. HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. No HFAs were observed when the Mach number was less than 5, suggesting there is a minimum threshold Mach number for HFAs to form. HFAs occur most preferentially for solar wind speeds from 550-600 km/s. Multiple THEMIS spacecraft observations of the same HFA provide an excellent opportunity to perform a spatial and temporal analysis of an HFA. The leading edge, tangential discontinuity inside the HFA, and trailing shock boundaries for the event were identified. The boundaries' orientations and motion through space were characterized. The HFA expansion against the solar wind was 283 km/s. The spatial structure of the HFA was deduced from multiple spacecraft observations. The HFA is thicker closer to the bow shock. The magnetospheric-ionospheric signatures of an HFA have been investigated using in-situ spacecraft observations and ground based observations. Magnetic field perturbations were observed by three GOES spacecraft at geostationary orbit and high-latitude ground magnetometers in both hemispheres. Observations from magnetometers located at different MLTs showed that the perturbation propagates tailward at 0.32°/s or 9 km/s (1.27°/s or 21 km/s) for the northern (southern) hemisphere, which is consistent with an HFA propagating tailward along the dawn flank. SuperDARN radar observations showed a change in plasma velocity shortly after the HFA was observed by THEMIS.
    • Improved Modeling Of Turbulent Transport: From Noise In Transport Models To The Parareal Algorithm Applied To Full Turbulence Codes

      Samaddar, Debasmita; Newman, David (2010)
      Turbulence and turbulent transport are ubiquitous in nature and are of fundamental importance in everything from the spread of pollution to confinement in fusion plasmas. In order to study this, turbulence models need to be as realistic as possible and one must also be able to evolve the turbulence and the profiles of the quantities of interest on transport (long) time scales. Improving turbulence simulations by the introduction of new techniques forms the basis of this research. One part of this work involved improving the performance of a 1D transport model by the addition of noise. On a more fundamental level, studying long time dynamics for turbulence simulations is very difficult even with the fastest computers available now or in the near future. To help overcome this difficulty, a new way of simulating turbulence has been presented, namely parallelizing in time. Time parallelization of a fully developed turbulent system is a new application. Parallelizing the space domain to computationally solve partial differential equations has been extensively used and is one of the most common forms of parallelization. In contrast, the Parareal Algorithm parallelizes the time domain and has been found to significantly reduce the computational wall time in many simpler systems. Despite its success in other less complex problems, it has not yet been successfully applied to a turbulent system (to the best of our knowledge). If efficiently applied, this algorithm will allow study of the turbulent transport dynamics on transport time scales - something that has heretofore been very difficult. In this work, the results of applying the Parareal Algorithm to simulations of drift wave turbulence in slab geometry in which the relative dominance of the polarization and E x B nonlinearities are tuned artificially, are presented. These turbulent systems are in many ways similar to neutral fluid turbulence models, so success of the Parareal scheme in them expands the prospect of a broader range of application to many other turbulent problems. This thesis also presents the results of a modification to the algorithm. A model to study and predict the parameters governing the convergence of the scheme is also explored.
    • The interaction of Io and the Jovian magnetic field: Io's Alfven wings and particle acceleration

      Dols, Vincent (2001-08)
      Conditions for the formation of an electric field along the field lines of Jupiter crossing the satellite Io are investigated by examining the properties of Io's Alfven wave. A three-dimensional self-consistent MHD model, using a simplified magnetosphere description, illustrates the formation of this electric field and of Io's related auroral emission in the Jovian ionosphere. The Alfven wing properties between Io and Jupiter are studied with a one-dimensional MHD model and a realistic magnetosphere. Any change in the Io/Jupiter system affects the structure of the Alfven wing and likely affects the structure of Io's auroral emissions. This emission is likely structured in multi-spots and the angle between the first spot and the instantaneous projection of Io is less than 3°. In the limited context of the 1D approximation, the acceleration mechanism is expected close to Jupiter.
    • Interaction of two tributary glacier branches and implications for surge behavior

      Knowles, Christopher P.; Truffer, Martin; Larsen, Chris; Newman, David; Wackerbauer, Renate (2018-05)
      A glacier surge is a dynamic phenomenon where the glacier after a long period of quiescence, increases its velocities by up to two orders of magnitude. These surges tend to have complex interactions with tributaries, yet the role of these tributary interactions towards glacier surging has yet to be fully investigated. In this work we construct a synthetic glacier with an adjustable tributary intersection angle to study tributary interaction with the trunk glacier. The geometry we choose is loosely based on the main trunk and tributary interaction of Black Rapids Glacier, AK, USA, which last surged in 1936-1937. We investigate surface elevations, medial moraine locations, and erosive power at the bed of the glacier in response to our adjustable domain and relative flux. A nonlinear relationship between tributary flux and surface elevations is found that indicates flow restrictions can occur with geometries like Black Rapids Glacier. These flow restrictions cause increased ice thicknesses up-glacier which can lead to surges via increased stresses.
    • Investigation of strongly ducted infrasonic dispersion using a vertical eigenfunction expansion of the Helmholtz equation in a modal broad band acoustic propagation code

      Edon, Robert Alexander; Olson, John V.; Fee, David E.; Szuberla, Curt A. (2015-12)
      This study investigates an infrasound propagation model created by the National Center for Physical Acoustics (NCPA) which is applied to atmospheric data with a strong temperature inversion in the lower atmosphere. This temperature inversion is believed to be the primary cause of a dispersed infrasonic signal recorded by an infrasound sensor array located on the Southern California coast in August, 2012. The received signal is characterized by initial low frequency content followed by a high frequency content tail. It is shown the NCPA model is hindered by limited atmospheric data and no ground truth for the source function which generated the received signal. The results of the NCPA model are shown to not reproduce the recorded signal and provide inconclusive evidence for infrasonic dispersion.