Physical Sciences and Mathematics Commons^™

Understanding The Zonal Variability In Cmip6 Projections Of Sahelian Precipitation, Emmanuel Ogwuche Audu

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The uncertainty in model projections of future precipitation across the Sahel has persisted across many generations of Earth System Models (ESMs), with some models predicting drying and others moistening across this region. These discrepancies in future projections pose a challenge for stakeholders and decision makers. Many projections of Sahel precipitation found in the ESMs participating in the sixth phase of Coupled Model Intercomparison Project (CMIP6) show a zonal dipole in precipitation trend, with moistening across the Central and Eastern Sahel and drying projected for the Western Sahel. Previous studies have connected precipitation variability across the Sahel to changes in various …

Polarimetric Radar Signatures In Significant Severe Left-Moving Supercells, Raychel Nelson

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Left-moving (LM) supercells, though rarer than right-moving (RM) supercells, may produce significant severe weather. However, there are very few existing studies on LM supercells, particularly polarimetric radar analyses. The upgrade of the nationwide Weather Surveillance Radar-1988 Doppler (WSR-88D) network to polarimetric capability and subsequent studies vastly improved understanding of RM supercells, but similar efforts have largely not been made for LM supercells. This study employs an automated polarimetric radar signature detection algorithm to examine a dataset of significant severe (hail ≥ 2.00”, wind ≥ 65 kts) LM supercells to quantify their polarimetric signatures. Comparisons are made with RM supercells to …

A Dual-Polarimetric Analysis Of A Large Sample Of Left-Moving Supercells, Ben Schweigert

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Supercells have been researched extensively since they were first described over 50 years ago. They are prolific severe weather producers, responsible for the most severe hail, severe wind gusts, and tornadoes. These rotating thunderstorms require attention from forecasters to protect life and property from their threats, most effectively done with Doppler radars. While extensive amounts of radar-based investigations have been completed, they focused almost exclusively on right-moving (RM) supercells, resulting in a knowledge gap surrounding their counter-rotating (left-moving, LM) partners. This study works to fill the void by developing a dataset of LM supercells and analyzing the dual-polarimetric features observed …

A Compilation, Analysis, And Categorization Of 403 Atmospheric And Climate Science Misconceptions, Haeli Leighty

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The National Association of Geoscience Teachers (NAGT) has listed the inaccessibility of research related to misconceptions in atmospheric and climate science as a Geoscience Education Research Grand Challenge (Cervato et al. 2018). This project was a direct response to this call for research and consisted of three distinct steps: 1) data gathering, which included reviewing the literature for relevant misconception data, 2) a qualitative analysis, which included compiling, organizing, and categorizing the data collected, and 3) a quantitative analysis, which included determining the prevalence of each misconception across topic categories, demographic categories, and over time. A total of 403 misconceptions …

Wonderstone And Its Connection To Liesegang, Microbes, And Beyond, Haden S. Mandery

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

In the western and southwestern United States, the term wonderstone is used to describe volcanic, volcaniclastic, and sedimentary rocks with variegated banding produced by iron oxide mineralization or staining. This iron oxide mineralization is typically described as Liesegang banding. In this paper I will (1) test if the banding in wonderstone follows the spacing and width laws characteristic of Liesegang, (2) identify the source of iron that ultimately precipitated in the bands, and (3) examine the role that microbes played in the formation of the mineralization in these rocks. I conclude that the iron oxide mineralization is not Liesegang banding. …

A Climatology Of Mesoscale Airmasses With High Theta-E, Charles J. Kropiewnicki

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

A Mesoscale Airmass with High Theta-E (MAHTE) is a narrow region of larger theta-e located on the cool side of an airmass boundary. MAHTEs typically possesses higher CAPE than the warm side of the boundary, creating a more favorable environment for severe convection. MAHTEs can also be characterized by larger low-level shear and lower LCLs and may also have a propensity for supporting tornadogenesis. The majority of MAHTE research to date has been comprised of case studies, and the prevalence of MAHTEs is not well understood. This project fills that knowledge gap by creating a climatology of MAHTE occurrence. This …

Comparison Of Ceneb And Cohyst Hydrologic Models Within A Common Domain In Central Nebraska, William R. Moak

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The Nebraska Department of Natural Resources (NDNR) has developed several hydrologic models to help effectively manage water resources in the state. These models guide water managers to allocate surface and groundwater supplies to a range of uses (irrigation, environmental protection, interstate water agreements) and evaluate the impacts of changes to the surface water-groundwater system (e.g., new wells, evolving recharge patterns). Two such models, the Central Nebraska (CENEB) model and the Cooperative Hydrology Study (COHYST) model cover north central and south central Nebraska, respectively, but the model domains overlap along a west-east strip between the Platte and Loup Rivers, enabling direct …

An Empirical Examination Of The Environmental Variability That Impacted Supercell Evolution, Longevity, And Severe Weather Production On 22 May 2019 In Oklahoma, Kyle D. Pittman

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Mesoscale environmental heterogeneity can have significant impacts on thunderstorm organization, evolution, longevity, and severe weather production. This study examines the 22 May 2019 thunderstorm event in Oklahoma, where a relatively broad area of strong instability and vertical wind shear existed along a synoptic boundary and in the open warm sector that would seem to support long-lived supercells and tornadoes. There were two particularly dangerous situation (PDS) tornado watches issued during the event, but few severe reports and no tornadoes formed in the watch that covered the southwestern portion of the state. Several tornadic supercells and many more severe reports occurred …

Crustal Structures Of Diebold Knoll And Adjacent Juan De Fuca Oceanic Crust From Integration Of Seismic, Gravity And Magnetic Data, Md Ariful Islam

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Cascadia Subduction Zone (CSZ) has a long history of devastating earthquakes as the Juan de Fuca plate subducts beneath North America, where an imminent megathrust earthquake is expected. Compared to other subduction zones, CSZ exhibits unusually low seismic activity, particularly in the central region with respect to relatively high seismicity zones to the north and south. Some researchers attribute this behavior to subducted seamounts, although their impact on seismicity remains poorly understood and highly debated in the literature. Examining subducted seamounts is challenging due to complexity of the overburden strata. That is why this study focuses on an isolated not-yet-subducted …

Exploring The Relationships Between Mammalian Functional Trait Distributions And Regional Biomes, With Application To Miocene Paleoecology, Devra Hock-Reid

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Paleoecology relies on understanding relationships between modern animals and their environment. Animals are adapted to niches in their environments, and those physical adaptations, or functional traits, are utilized as proxies to interpret aspects of paleo-ecosystems. Much is known about individual functional traits in extant mammals and their relationship to the environment. Less is known about how multiple functional traits across a community can be utilized for paleoecological interpretations. I develop models utilizing traits in mammalian communities at the biome level. For Chapter 1, I build a model for North American regional biomes using mammalian trait frequencies. I quantify changes in …

Radar Signatures In Tropical Cyclone Tornadic And Nontornadic Supercells, Michaela Wood

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Tropical cyclones (TCs) contain highly-sheared environments that are conducive for supercell thunderstorms. These TC supercells sometimes produce tornadoes, often with little warning. Given the often-close proximity of tornadic and nontornadic TC supercells, environments may not be well-distinguished, pointing to the potential value of radar observations. In this study, dual-polarimetric radar signatures of a sample of TC supercells are examined in the context of known supercell structure and microphysics. Tornadic and nontornadic TC supercells are compared with their midlatitude counterparts, and the environments and characteristic structure of these storms are shown to be notably different. An attempt is made to distinguish …

Impact Of Lithological Variation And Topology On The Connectivity And Intensity Of Fracture Networks In Carbonates, Fahad Qassim

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Assessing fracture network connectivity in reservoirs remains a challenging task because of the complex nature of fracture networks at various length scales, which significantly impacts fluid flow behavior. Outcrop studies are essential for understanding subsurface fracture networks because intersecting fracture sheets' length, orientation, height distribution, and, therefore, network connectivity and intensity are difficult to measure from wellbores and are typically below seismic resolution. Nevertheless, fracture network connectivity is a crucial parameter and a critical factor in understanding, evaluating, and predicting fluid flow behavior in hydrocarbon reservoirs, aquifers, hazardous waste and CO₂ storage systems, and geothermal energy exploitation. Moreover, fracture …

Human And Hydrologic Influences On Nebraska's Endangered Rainwater Basin Wetlands, Sarah Thompson

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Over half of wetlands in North America have been lost or degraded. Rainwater Basin (RWB) wetlands, located in south-central Nebraska, are a primary example of such loss; an estimated 90% have been destroyed by land conversion for agriculture. Remaining RWB wetlands are often embedded in row-crop fields, where they are threatened by altered surface water runoff flow, drainage features, and excess sediment inputs. Efforts at the state and federal level have been made to preserve this wetland complex due to the critical stopover habitat these wetlands provide for migratory birds. Land managers work to maintain sufficient water levels during migratory …

Impacts Of Physical Parameterization Schemes And Soil Moisture Initialization On Boundary Layer Evolution In The Weather Research And Forecasting (Wrf) Model, Grace Cutting

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Numerical weather prediction (NWP) models have become a necessary addition to the atmospheric research community over the last several decades, and atmospheric modeling has been used internationally for numerous operational and research purposes. NWP models contain a vast number of combinations of physical and dynamical parameterization schemes; however, they are not always accurate in forecasting weather phenomena at a particular location, as different combinations of parameterization schemes represent differing conditions. Weather Research and Forecasting (WRF) model simulations were run to explore which of the commonly used planetary boundary layer (PBL) schemes best represented upper-air data (as well as PBL evolution) …

Using Remote And In Situ Observations From Torus To Investigate A Preexisting Airmass Boundary And Its Influence On A Tornadic Supercell On 28 May 2019, Kristen Axon

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

During the 2019 field phase of Targeted Observation by Radars and UAS of Supercells (TORUS), a preexisting airmass boundary was sampled on 28 May 2019 in north-central Kansas in close proximity to a tornadic supercell. This work hypothesized that the preexisting airmass boundary was associated with a mesoscale air mass with high theta-E (MAHTE) that favorably interacted with the tornadic supercell to increase the likelihood of tornadogenesis. Observations from TORUS including mobile mesonets, unoccupied aerial vehicles, soundings, and ground-based mobile radar were used along with GOES-16 visible satellite imagery, Kansas mesonet surface stations, and KUEX WSR-88D data to investigate this …

The Diatom Dark Ages: Identification Of Mid-Cretaceous Arctic Platform Diatoms From The Basal Transgression Of The Kanguk Formation, Devon Island, Nunavut, Canada, Megan Heins

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The lower part of the mid-Cretaceous Kanguk Formation (Lower Turonian interval) contains an important paleontological record crucial to the characterization of a poorly known interval of fossil marine diatoms history. Kanguk Formation mudstones are exposed in a ~200 m-thick section on Devon Island, Nunavut, Canadian High Arctic. Diatoms at this location are well-preserved due to shallow burial on this Arctic Platform site. The rock sequence was protected from glacial erosion that removed much of the Cretaceous record by being down-faulted in a linear graben. Study of these well-preserved fossil diatoms allows for a documentation of the assemblage, identification of potentially …

An Investigation Of Water Obstructions And Related Weather Conditions For Nebraska Roadways, Logan Bundy

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Roadway resilience across the 10,000 miles of road and 3,500 bridges in Nebraska is critical to the economic success of production and logistics. In a state where historical flooding scenarios, such as the one in March 2019 that caused $150 million in damage, could potentially be increasing, it has become essential to understand the spatial and temporal distribution of high-frequency water obstruction areas on roadways. Using Nebraska Department of Transportation (NDOT) historical water obstruction data from June 2016 through August 2021, statistical and spatial analyses were conducted to quantify the relationship between water obstructions and their associated meteorological conditions, and …

Comparing Polarimetric Signatures Of Proximate Tornadic And Non-Tornadic Supercells In Similar Environments, Devon Healey

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

While much research has shown that characteristics of the environment surrounding supercells can potentially indicate their likelihood to become tornadic, it is not uncommon for tornadic and non-tornadic supercells to coexist in seemingly similar environments. In these situations, it is difficult operationally to separate tornadic from non-tornadic supercells using environmental observations alone. Given that tornadic and non-tornadic supercells have been found to coexist in similar environments, something must be occurring beneath the observational and/or model gridscale that is supporting tornadogenesis in some supercells while inhibiting it in others. This study examines dual-polarimetric radar signatures of proximate tornadic and non-tornadic supercells …

Using Field Scale Electrical Data To Understand Real-Time Agricultural Water Delivery, Bradley Dowell

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Areas across the High Plains (Ogallala) Aquifer region are experiencing unsustainable groundwater level declines and impacts to streamflow due to increasing human influence, posing challenges for sustaining future agricultural economies and groundwater resources. State and local agencies manage water using groundwater models, which are not at the same temporal and spatial scale as water management on farms. Well-informed agricultural water usage cannot be achieved without reliable and cost-effective water use at farm scale. Water meters are expensive and rarely installed unless required by the state or other regulatory agency; however, most center pivots have their own power supply, which reports …

Toward The Understanding Of The 2018 Arnold, Ne Earthquake Cluster: Relocation Of Hypocenters And Establishment Of New Gravity Base Stations, Kris Guthrie

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

In 2018, 27 unexpected earthquakes occurred in central Nebraska near Arnold. These earthquakes have no readily apparent cause and no evidence of the responsible fault system is seen at the surface. A joint analysis of vintage, regional gravity and magnetic datasets before the first earthquake revealed a lineament that could represent a pre-existing fault system. New high resolution potential fields data are needed to confidently map the subsurface features around the cluster. To design a survey and collect the data, the following tasks need to be addressed: [1] The earthquakes’ hypocenters need to be improved (relocated) to increase the efficiency …

An Analysis Of Associations Between Polarimetric Supercell Signatures, Erik Green

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Supercell thunderstorms produce unique polarimetric radar signatures that are not often observed in unorganized deep convection. Repetitive signatures include deep and persistent differential reflectivity (Z_DR) columns and the Z_DR arc signature, which are both indicative of thermodynamic and microphysical processes intrinsic to supercells. Prior investigations of supercell polarimetric signatures, both those observed by operational and research radars, and those simulated numerically, reveal positive correlations between the Z_DR column depth and cross-sectional area and quantitative characteristics of the radar reflectivity field. This study expands upon prior work by incorporating a dataset of discrete, right moving supercells …

Implications From Uranium-Series Disequilibria In A Bi-Lithologic Melt With Varying Lithospheric Caps, Juliet Messer

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Both spreading rates and local magma supply to mid-ocean ridges affect crustal construction styles and ridge morphology, alternately leading to either asymmetrical (detachment faulting) or symmetrical faulting styles. Uranium-series isotopic disequilibria in mid-ocean ridge basalts (MORB) may provide insight into how melt supply variations relate to ridges’ accretion styles, a processes that are not well understood. I use Reactive Porous Flow (RPF) equilibrium and disequilibrium modeling to simulate U-series disequilibria at mid-ocean ridge (MOR) generated by melt supply variations at both asymmetrical and symmetrical ridge segments.

Guided by my modeling, I predict that enhanced melt contributions from enriched pyroxenitic mantle …

Biostratigraphy Of Paleogene Diatom Assemblages In The Southern Ocean, Angela Kaup

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The record of siliceous microfossil sedimentation in the high latitude South Atlantic Ocean has great potential for dating seismic and stratigraphic units. Over the last several decades, scientists have documented diatom biostratigraphic record from sediment cores and drill cores in the Falkland Plateau and Maurice Ewing Bank region, as well as other areas of the Southern Ocean, and a robust chronostratigraphic framework is available for Neogene sequences. Given the complicated nature of ocean bathymetry, tectonic plate motion (vertical and lateral), and ocean current flow, the sedimentological evolution of this oceanic region is not well understood. Sampling sediment cores at high …

Assessing Deep Convection Initiation In A Mountain-Valley System Using Unoccupied Aircraft System Observations, Alexander Erwin

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Forecasts of the timing and location of deep convection are inadequate, as are scientists’ understanding of the dominant controlling mechanisms. The Lower Atmosphere Process Studies at Elevation, a Remotely-piloted Aircraft Team Experiment (LAPSE-RATE) field campaign, which took place in the San Luis Valley (SLV) of Colorado during July 2018, aimed to use in-situ observations to develop a deeper understanding of the processes relevant to deep convection initiation (DCI). The campaign resulted in a unique dataset, collected by a network of unoccupied aircraft systems (UAS) in a unique geographic setting, which can be used to examine the impact of terrain and …

Developing A Database Of Seismic Data Over The Cascadia Subduction Zone, Khawlh Al Farsi

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

An inevitable megathrust earthquake is expected in the Cascadia subduction zone that will affect the population of the coast of southwestern British Columbia and the northwest of the United States. In this active tectonic margin, the Juan de Fuca oceanic plate is subducting beneath the North American continental plate, causing unevenly distributed seismic activity. The major goal of this geophysical research project is to study the tectonic structures of the Cascadia subduction zone in order to comprehend the geology of the region and investigate the seismic hazards. The primary objective of this project is to develop a geophysical database of …

Geological Structures And Crustal Architecture Of The Cascadia Subduction Zone From The Integration Of Multiple Geophysical Datasets, Asif Ashraf

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The Cascadia subduction zone (CSZ) has a high potential for an inevitable and devastating megathrust earthquake. This margin is characterized by a complex seismicity pattern. Particularly in Oregon, there is a seismically quiescent zone bounded by high seismicity regions to the north and south. To comprehend these variations in seismicity, it is important to study the differences in crustal architectures and physical properties (densities and magnetic susceptibilities) along the CSZ. The primary objectives are to develop two plate-scale 2D integrated models through different seismicity zones and to map major tectonic structures from filtered potential fields. The Juan de Fuca oceanic …

Drone-Based Magnetic Surveying In Eastern Nebraska, Sulaiman Albadi

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

A magnetic survey is one of the methods used by scientists to detect subsurface features. Magnetic surveys can be carried out by walking on the surface of the earth with a magnetic field reading device called a magnetometer. Alternatively, a magnetometer can be installed on a moving platform (aircraft, boat, drone, bicycle) to conduct a more efficient magnetic survey. The geophysics team at the University of Nebraska at Lincoln assembled a drone-based magnetic survey system in 2019 (Jacobson and Filina, 2019) that has proven effective in magnetic readings over the Northern Bounding Fault (NBF) in eastern Nebraska (Jacobson and Filina, …

The Analysis Of Groundwater Recharge In Mongolia Using Vadose Zone Modeling, Khulan Batsukh

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Knowledge of groundwater recharge (GR) is vital for optimal water resources management under an arid continental climate. However, in vast territories such as Mongolia, direct measurements of GR are unfeasible because they mandate excessive costs, stemming from time-consuming and labor-demanding efforts. A valid alternative to direct measurements is numerical models based on the monitoring of precipitation (P) and evapotranspiration (ET) for simulating GR. While direct measurements of ET are logistically problematic and unpractical for large-scale applications, a reliable prediction may be derived from crop reference evapotranspiration (ET₀) which is calculable …

Analysis Of Winter Weather Conditions And Their Relationship To Crashes In Nebraska, John Cecava

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Adverse weather conditions: such as changes in visibility, precipitation, wind speed, temperature, and road surface conditions, substantially impact highway and interstate safety. Therefore, an investigation into the winter weather conditions during highway and interstate crashes in Nebraska was conducted. Crash data were obtained from the Nebraska Department of Transportation (NDOT) for the years 2008 to 2018. In order to separate the non-winter weather related crashes and the winter weather related crashes, six filtrations were applied to make this possible. These filters were based on a few crash parameters: road classification, alcohol, and crash severity, and weather parameters within the crash …

Case Studies Of Alberta Clipper Systems And The Impacts On Winter Weather Road Maintenance, Cameron Wunderlin

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Winter weather can cause profound impacts to a variety of economic sectors in the mid-latitudes. In the Great Plains of North America, one sector that is highly impacted by winter weather is road transportation. The burdens to road transportation caused by winter weather have led to the adoption of a Maintenance Decision Support System (MDSS) by the Nebraska Department of Transportation (NDOT). Using both observational and numerical weather model data, NDOT-MDSS generates both winter weather forecasts and winter road maintenance recommendations. Little is known about how well NDOT-MDSS is forecasting conditions for different winter weather events. Using a case study …