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ItemDynamics and Observational Implication of Close-in Exoplanets(Georgia Institute of Technology, 2024-07-28) Chen, ChenWith more than five thousand exoplanets discovered, it unveiled significantly diverse orbital configurations, contrasting with those in our Solar Systems and confronting classical understanding of planet formation. For instance, the prevalence of observed close-in exoplanets that lie within the orbit of Mercury up to ~0.01 AU brings up questions about their formation, as their current orbit distances can be within or close to the dust sublimation zone. These planets could initially formed at a further distance, and then migrate inward. However, why and how the configuration of these close-in systems differs from the Solar System is still puzzling. Investigating their dynamical and physical properties can help us gain deeper insights into the planetary system formation and evolution beyond the Solar System and better understand their habitability. Under this context, this thesis presents the characterization of the dynamics and the identification of the physical properties for close-in systems. In the first work, I focused on the dynamics of ultra-short-period planet (USP), which is defined as the planet orbiting its host star shorter than one day. The USPs orbit in close proximity to their stars within the sublimation zone. This extreme object typically has a larger period ratio and higher mutual inclination with its outer companion, comparing to other systems without it. To characterize the dynamics of USP systems, I utilized secular simulations and developed an analytical method to investigate the mutual inclination evolution of the USP system. The stellar oblateness (J2) plays an important role in the dynamics. It can excite the mutual inclination between planets by precessing their orbital angular momentum at different rates, and it decreases with time due to magnetic braking. Therefore, we focused on the dynamical effects of J2. I successfully identified the formation channel of the Kepler-653 system with different initial conditions. The result suggests that either USP planets formed early and needed significant inclinations or they formed late when their host stars rotated slower (smaller J2). In the second work, I characterized the physical properties of the close-in planets by employing deep learning techniques to predict the parameters of exoplanets. Most planets are discovered from transit method without the measurement of their masses. However, mass is important to better understand the composition and formation mechanism of planets. One way to determine the mass is through transit timing variation (TTV). The TTV encodes rich dynamical information as it is contributed by perturbations from planets, and provide a powerful method to estimate planetary masses and orbital parameters. The traditional Markov Chain Monte Carlo (MCMC) method incorporates TTV to predict the planetary properties, however, MCMC is computationally expensive, and highly sensitive to the prior distribution. Especially, when the system is with only one planet transit, the properties of non-transit planet are even harder to obtain. Deep learning techniques are able to tackle these challenges. It can predict the exact values of the properties, and there is no need to consider the specific prior distribution. Therefore, I designed a deep learning model to determine the orbital parameters and mass of non-transit planet with transit information as input, focusing on single transit planetary system. The deep learning model I trained gives an overall fractional error of ~1% on the predictions of the testing set. I also utilized the model to make predictions on the real system, Kepler-88. This work can contribute to the design of observational missions aiming to search companions of single transiting systems.
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ItemThe Development of Georgia Critical Minerals Partnerships: An example from Kaolin Mining Operations SE USA. A White Paper Report of the First Meeting of Georgia Essential Minerals (GEMs-1)(Georgia Institute of Technology, 2024-05-14) Elliott, W. Crawford ; Schroeder, Paul A. ; Tang, Yuanzhi ; Lemke, LeeNovel resources of the rare earth elements (REE) were discovered recently in the kaolin ore deposits in the Georgia Coastal Plain. This discovery also showed that it is possible to coproduce significant amounts of REE during the normal course of mining and processing mined kaolin ore. REE are among the 50 critical minerals identified as being vital to technological and economic development and also on which we are dependent on international supplies per the United States Geological Survey. A partnership approach is needed to bring these metals from mine to market. And in doing so, it will address the need for reliable domestic supplies of the rare earth elements. The coproduction, mining, extraction, and forming a saleable rare earth product is beyond the reach of any one group. A partnership is desirable given the many kinds of tasks involved to bring the REE from outcrop to market. Among the important tasks are the identification of the state-of-the-art mining operations to concentrate the REE and identification of extractive technologies to produce saleable REE materials from coproduced REE resources. The Georgia Critical Minerals Partnership is being created to derive plans to identify and to promote the technological developments needed for the coproduction of REE from mined kaolin, their extraction, and aggregation to form saleable mineral products. This Partnership will necessarily bring relevant academic, government, and industry to derive these plans and strategies to bring the mined coproduced rare earths to market. The Partnership will be a vehicle to derive the needs for funding for accomplish the characterization of REE resources, calculating the resource base of REE, identifying extractive technologies and saleable REE products. The Partnership will highlight the governmental resources needed for resource evaluation and constructive environmental stewardship to permit the mining and extraction of the coproduced REE. It is projected that amounts of the REE resources in the coproduced kaolin mine waste warrants co-oping with industry to bank their concentrates of coproduced REE. Finally, a trained workforce must be in-place to make these plans a reality. The needed workforce includes trade, technical, professional, and managerial ranks. Through this partnership and its plans to mine and create saleable REE mineral products, Georgia will be better positioned to accomplish both the attraction of the high-tech industry needing REE and to be able to provide locally sourced REE to these industries for their growth and development. This Partnership will hopefully serve as a model for other regions to follow.
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ItemAssessment of coral ecosystem community calcifier composition using trace element cycling via ICP techniques(Georgia Institute of Technology, 2024-04-29) Wyatt-Ngom, Sokhna AminataCoral reefs are an integral part of coastal ecosystems. They protect coastlines from storms, provide habitat for 25% of all marine life and contribute to local economies through tourism and fisheries. Unfortunately, climate change-related stressors (such as increased sea surface temperatures and acidification) associated with anthropogenic emissions of fossil fuel carbon dioxide (CO2) have contributed to declines in coverage and health of coral reefs throughout the world. Without healthy coral reefs, many coastal communities lose protection, significant amounts of marine life lose their homes and entire coastal ecosystems can collapse. Therefore, it is essential to quantify the rate of this global coral reef decline is of great concern and has been made possible through measurements of variability in seawater constituents (such as precipitation rates found via sedimentation analysis) that serve as metrics of metabolism, net ecosystem productivity (NEP) and net ecosystem calcification (NEC), on reefs. These traditional measurements are limited in their ability to measure precipitation, dissolution, and calcification rates. Studies have found precipitation rates in the same area are 40% higher than previously thought from sedimentary analysis (Steiner et al. 2014;2018). More nuanced indicators of calcification dynamic on reefs (such as trace element analysis) could be key in obtaining accurate calcification rates alongside precipitation and dissolution. Knowing this information can then greatly assist in creating adaptation and mitigation strategies for reefs under m these continued stressors. Here, I apply inductively coupled plasma¬-optical emission spectroscopy (ICP-OES) to measurements of reef seawater strontium-to-calcium (Sr/Ca) ratios from Tetiaroa Atoll, French Polynesia collected over two complimentary diel field campaigns in October 2015 and January 2016. In this study, we look at the differences and dominance of marine organisms made up of calcite or aragonite. Calcifiers made from calcite act as “glue” for coral skeletal structures, are more soluble in acidic conditions and have a partition coefficient (KD) at or around 0.35. Calcifiers made of aragonite become the foundation for habitats on a reef, are less soluble in acidic conditions and have a partition coefficient (KD) at or around 1.02. The next step is to apply a Rayleigh Mixing model to decompose the observed temporal variability in Sr/Ca ratios into net ecosystem partition coefficients (KD) that characterize the percent contributions of calcite and aragonite to hourly-to-daily gradients in calcification This measurement is of importance as it can give us a baseline for calcifier community dynamic within a reef, that assist in the monitoring of the reef in a time of warming and acidifying oceans. Additionally, establishing this technique in a relatively pristine reef (like Tetiaroa) allows for its calibration- for future applications in more degraded reefs- ultimately expanding our toolkit for conservation efforts. Primary results include: 1. ICP-OES captures reproducible variability in Sr/Ca seawater ratios on par with previously published mass spectrometry techniques having RSD values of at or below 0.1 mmol/mol. 2. The temporal variability in Tetiaroa seawater Sr/Ca ratios may be seasonally influenced. Diel (24 hour) variability in data from October 2015 have a broader a range of 0.155 mmol/mol when compared to January of 2016 with range of 0.031 mmol/mol. 3. KD values found based on observed temporal variability can give great insight on calcification dynamics on seasonal timescales and implies that while corals remain the dominant calcifier throughout the seasons, crustose coralline algae may play more of a role in NEC in January (winter) in Tetiaroa Atoll, French Polynesia. The overall results of this study suggest Sr/Ca in seawater is a promising proxy for monitoring reef calcification and community composition within rapidly warming and acidifying oceans. Further methodological advances in the development of this proxy may be made possible through the pursuit of high resolution and high precision mass spectrometry techniques.
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ItemInfluence of Magnetic Field Line Draping on Charged Particle Irradiation of Europa's Surface Ice(Georgia Institute of Technology, 2024-01-17) Addison, PeterEuropa, the smallest of the Galilean moons of Jupiter, orbits within its parent planet's inner magnetosphere. When the Galileo spacecraft visited Europa in the late 1990s, its magnetometer measured signatures consistent with a secondary magnetic field centered at the moon. It was found that such an induced field could only be generated by a highly-conducting, liquid water layer locked beneath the moon's icy crust. The presence of this subsurface ocean has since made Europa one of the most promising locations to search for extraterrestrial life. Analysis of the ocean is, however, thwarted by the 10s to 100s of kilometer thick ice shell under which it is encased, and any investigation is (for now) limited to the moon’s surface. Unfortunately, the surface is exposed to a harsh radiation environment. At its location within Jupiter's magnetosphere, Europa is located within a region of dense, energetic magnetospheric plasma which hammers down on the surface. This charged particle bombardment makes the upper surface uninhabitable to any organic signatures, drives surface chemistry, generates the moon's dilute exosphere by ejecting neutral material from the surface, and is potentially harmful to spacecraft. Characterizing the intensity and spatial distribution of this charged particle irradiation is therefore critical not only to understanding the evolution of Europa's surface and exosphere, but is also of utmost importance to spacecraft safety. The impact locations of charged magnetospheric particles onto Europa's surface is determined by the dynamics of these particles both in Jupiter's global magnetosphere and in the moon's local electromagnetic fields. The dense plasma within Jupiter's equatorial plasma sheet continually washes over Europa's orbital trailing hemisphere. This flowing plasma interacts with the induced field from Europa's subsurface ocean, as well as electric currents within the moon's ionosphere, drastically warping the background Jovian field. Such perturbations may deflect particles and shield the moon's surface, or focus irradiation onto regions which previous studies have determined to be relatively "safe". In order to develop a comprehensive picture of magnetospheric particle irradiation at Europa and its effect on the surface, we combine a three-dimensional hybrid model of the moon's perturbed electromagnetic environment with a relativistic particle tracer in order to map how the field perturbations affect the irradiation patterns. We calculate ion and electron irradiation patterns, energy deposition, and sputtering rates, and compare our results with observations from both the Galileo spacecraft and Hubble Space Telescope. We find that the electromagnetic field perturbations strongly affect the irradiation patterns of magnetospheric ions, but not of electrons, and that exogenic particle irradiation is essential to explain several observed features of Europa’s surface and exosphere.
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ItemMicrocat, Aquadopp, and ADCP data from the 2020-2022 Labrador Sea eastern boundary mooring array as part of the Overturning in the Subpolar North Atlantic Program (OSNAP)(Georgia Institute of Technology, 2024-01) Pickart, Robert S.The Overturning of the Subpolar North Atlantic Program (OSNAP) is an effort to determine the strength of the meridional overturning circulation and associated heat and freshwater fluxes in the subpolar North Atlantic. It is a collaborative program with scientists from the U.S., U.K., Netherlands, Germany, France, Canada, and China. Together, moorings were deployed across the boundaries of the Labrador Sea, Irminger Sea, Iceland Basin, and eastern subpolar North Atlantic. The OSNAP West array consists of 11 moorings spanning from the west Greenland shelf to the base of the continental slope. The 6 shelf moorings are bottom tripods, while the five offshore moorings are tall moorings. The tripod moorings contained a weak-link extension to obtain hydrographic measurements 50 m below the surface. Velocity was measured using a combination of Aquadopps and acoustic Doppler current profilers (ADCPs), and the pressure, temperature, and salinity were measured using MicroCATs. The time period of the deployment of the array was August 2020 to August 2022. All of the data have been calibrated, processed, and quality controlled.
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ItemUncertainties in Projections of Tropical Precipitation and Atmospheric Circulation and Their Remote Impacts(Georgia Institute of Technology, 2023-12-10) Lu, KezhouMy doctoral work focuses on understanding anthropogenic responses of precipitation and atmospheric circulation by employing both statistical methods and climate models of varying levels of complexity. My research has two main goals: (1) to understand the forced response of tropical air-sea interactions across different time scales and their subtropical impact, and (2) to investigate the reasons underlying the uncertainties in climate models when simulating tropical and extra-tropical climate. My dissertation research comprises four individual projects. For my first project, I have explored the mechanism of how the Walker circulation (WC) responds to CO2 forcing across different time scales. The WC, a significant tropical atmospheric circulation spanning both horizontally and vertically, plays a crucial role in the tropical climate and is closely related to phenomena such as the Madden–Julian Oscillation and El Nino-Southern Oscillation. The prevailing consensus suggests that the long-term weakening of the WC is primarily driven by the sea surface temperature (SST) warming caused by increased greenhouse gases, while the fast response of the WC appears largely independent of changes in SST. However, my findings indicate that the air-sea interactions play a substantial role. By analyzing data output from Coupled Model Intercomparison Project Phase 5 (CMIP5) under abrupt4xCO2 scenarios, models with a stronger air-sea coupling in the equatorial Pacific are discovered to simulate an initial strengthening of the WC following the external forcing, which contrasts with the long-term response. Conversely, models characterized by weaker air-sea coupling simulate a monotonically weakening of the WC. My results suggest that the inter-model discrepancy in the WC changes is associated with then uncertainty in the fast component. My second project focuses on understanding the summer North Pacific subtropical high (NPSH). As part of the planetary wave system, the NPSH integrates both tropical and extra-tropical impacts on the monsoons and typhoons over East Asia and hydroclimate over California. Given its considerable socioeconomic significance, reliable future projections of the NPSH are crucial for preparing adaptation plans. However, state-of-the-art climate models exhibit diverging responses of the NPSH to anthropogenic CO2 forcing. This project has revealed that model variability in the future projection of the summer NPSH originates from both inter-model SST-driven and non-inter-model SST-driven uncertainties in the tropical precipitation. Specifically, I investigate the connection between the tropical precipitation and the NPSH by modifying the diabatic heating in both a baroclinic stationary wave model and a comprehensive climate model, i.e. the Community Atmospheric Model version 5 (CAM5). Drawing upon the knowledge acquired from the previous two chapters, my third project has explored how the tropical air-sea interaction and the summer NPSH are influenced by anthropogenic forcing, as well as their interplay. I have discovered that the inter-model spread in projecting the fast changes of the WC directly contributes to the inter-model spread in tropical SST responses. By analyzing CMIP5 and CMIP6 data under abrupt4xCO2 scenario, models with a stronger tropical equatorial Pacific air-sea coupling simulate a strengthening of the WC and a La Nina-like central Pacific cooling. And this La Nina-like SST anomaly induces anomalous tropical precipitation and further modulates the NPSH via the Matsuno-Gill wave response. During the collaboration with my advisor on the fourth project, we have found considerable inter-basin variations in the future projection of the tropical Hydrological sensitivity (HS) regardless of how SST warms. I have further demonstrated the remote impact of the inter-basin discrepancy in HS on land precipitation and surface temperature by understanding the corresponding tropical-extra-tropical teleconnections. Specifically, I have analyzed the atmospheric circulation response induced by tropical precipitation with and without inter-basin discrepancy in HS by conducting diabatic heating adjustment experiments in CAM5.
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ItemObservations of peroxyacyl nitrates in polluted and remote troposphere(Georgia Institute of Technology, 2023-08-01) Lee, Young RoEmissions of volatile organic compounds (VOCs) and their photooxidation with nitrogen oxides (NOx) play a significant role in atmospheric chemistry and have substantial effects on air quality. Understanding these processes in the ambient environments is a challenge, in part, due to uncertainties in emission sources and the complex chemical evolution of emissions. This dissertation leverages a comprehensive suite of ground-based and airborne observations to investigate the impacts of VOCs-NOx photochemistry on atmospheric trace gas compositions, both in heavily polluted and pristine environments. In particular, this work focuses on observations of peroxyacyl nitrates (PANs) to provide a detailed diagnosis of photochemistry in the regions discussed throughout the dissertation. East Asian countries such as South Korea and China have experienced severe air pollution problems. In this work, extensive observations of primary and secondary pollutants were conducted in two locations: a remote ground site in the Yellow River Delta, China, during the Ozone Photochemistry and Export from China Experiment (OPECE) in 2018, and a petrochemical producing region in South Korea during the Korea-United States Air quality (KORUS-AQ) campaign in 2016. Our findings during the field observations indicated that both regions are characterized by heterogeneous VOC composition with substantial emissions of alkenes and aromatics. Photooxidation of these VOCs led to efficient ozone production in a radical-limited environment. In addition, elevated levels of peroxyacetic nitric anhydride (PAN), as well as rarely measured homologs such as peroxybenzoic nitric anhydride (PBzN) and peroxyacrylic nitric anhydride (APAN), illustrated the unique atmospheric chemistry in East Asian environments. This dissertation presents global-scale airborne observations of PAN from the NASA DC-8 research aircraft during the ATmospheric Tomography (ATom) campaign. The focus of this investigation was on PAN observations in remote tropospheric regions such as over the Pacific and Atlantic Oceans. We found that PAN over remote oceans is significantly influenced by relatively simple sources including anthropogenic and biomass burning emissions. Notably, biomass burning has a dominant and persistent impact on the global distribution of PAN. Based on a diagnostic evaluation using observations, this work suggests that accurate model treatment of biomass burning can improve prediction of PAN in the remote troposphere. Lastly, the characterization of a low-activity 210Po ion source with an initial activity of 1.5 mCi was performed for use with iodide-chemical ionization mass spectrometry (I--CIMS). We demonstrated that the low activity source is a viable substitute of higher activity radioactive source, offering advantages in terms of reduced regulatory burden during storage and shipping. The performance of the low activity source is illustrated using airborne measurements of PANs during the ATom campaign.
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ItemPhotolytic Mass Loss of Secondary Organic Aerosol Derived from Photooxidation of Biomass Burning Furan Precursors(Georgia Institute of Technology, 2023-07-31) Shin, NaraDirect photolysis as a potentially important chemical loss pathway for atmospheric organic aerosol (OA) is increasingly recognized, but remains highly uncertain, particularly for secondary organic aerosol (SOA) derived from biomass-burning (BB) precursors. Here we present the measurements of photolytic mass change of SOA derived from the photooxidation of three furan precursors, 3-methylfuran, 2-methylfuran, and furfural in an environmental chamber for both dry and humid conditions. The SOA was collected on crystal sensors, and the mass losses by photolysis under 300 nm and 340 nm UV were continuously monitored using a highly sensitive quartz-crystal microbalance (QCM). By incorporating measurements and modeling, our results suggest that SOA from furan species can lose 10-40% mass by direct photolysis under solar radiation over their typical tropospheric lifetime. The mass loss fraction is well correlated with the mass fraction of nitrogen-containing compounds, as these species can largely enhance light absorption cross-section and readily undergo photodissociation under UV light.
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ItemUtilizing Subsurface-Dwelling Foraminifera for Quantitative Paleoclimate Reconstructions(Georgia Institute of Technology, 2023-07-27) Lakhani, Karim Q.Foraminifera are useful tools for paleoclimatology (how the climate was different in the past) with many proxies for key ocean variables in their shells. Subsurface-dwelling foraminifera have been underutilized in paleoclimate due to their inherent habitat uncertainty; much research with these species has been qualitative in the past. I outline a methodology for using these species quantitatively for paleoclimate reconstruction and apply it to the Last Glacial Maximum (LGM). Firstly, I compile a database of foraminiferal data to quantitively estimate the error in their habitats. Using these uncertainty estimates, I describe a regression method to estimate an ocean profile that can reconstruct important features in the ocean such as the thermocline. Using five species of foraminifera that live in the surface, subsurface, and bottom of the ocean, this method recreates large scale features in the thermocline across the Tropical Pacific as well as changes between the Holocene and LGM at published core sites. Finally, I apply this method to a dataset of LGM foraminiferal data for sites across the Tropical Pacific. After filling in the data gaps for these sites, I find that there were heterogenous changes in the Tropical Pacific thermocline, with no change in the Western Pacific thermocline and a deepening at some sites in the Eastern Pacific. Looking along a transect in the Western Pacific, I find that there are structural differences between the profiles estimated from LGM data and the Holocene climatology, suggesting a change in atmospheric circulation during the past. By improving the ability to utilize these recorders of subsurface ocean conditions, we can better understand how climate was different in the past and how well climate models can recreate those differences.
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ItemSurface Gravity Waves in Global Climate Models: Development, Evaluation and Optimization(Georgia Institute of Technology, 2023-07-25) Ikuyajolu, Olawale JamesSurface gravity waves play a critical role in several processes at the air-sea interface, including mixing, coastal inundation, and surface fluxes. Yet wind–wave processes are usually excluded from Earth system models partly due to a lack of physical understanding and the high computational costs of spectral wave models. Most wave modeling studies utilize uncoupled short-term simulations and focus on the upper ocean. The impacts of wind-wave processes on coupled climate variability have yet to be thoroughly evaluated. This all underscores the need to advance surface gravity wave modeling frameworks within general circulation models (GCMs). Herein, the first half of this thesis partly addresses the high computational cost of running spectral wave models on a global grid. I identify the wave action source terms as the most computationally intensive part of the spectral wave model WAVEWATCH III (WW3), and then accelerate them on Graphics Processing Units (GPUs) using OpenACC. An average speedup of 1.4x was achieved, resulting in a reduction of 35-40% in runtime and resource usage. In the second half of this thesis, I incorporated a wave-state dependent bulk formula by fully coupling WW3 to the Energy Exascale Earth System Model (E3SM). Current state of the science GCM bulk parameterizations estimate the sea-state roughness as a function of surface wind speed, ignoring wave effects. The newly implemented parameterization includes two primary wave effects: first, a wave-state dependent surface roughness computed by WW3; second, the alteration of momentum flux from the atmosphere to the ocean due to wave growth and dissipation. I conducted numerical experiments with this new parameterization to investigate the sensitivity of the mean climate and Madden-Julian Oscillation (MJO) to different bulk flux parameterizations and the role of waves in air-sea coupling. My results highlight that discrepancies between bulk algorithms have nonnegligible impacts on mean climate such as ocean heat content, sea-ice concentration and a 2℃ difference in sea surface temperature in the North Atlantic. Also, the proper treatment of air-sea coupling via the inclusion of wave-induced effects improves the simulation of MJO. Most importantly, the analysis emphasizes the importance of considering the role of waves in redistributing momentum flux between the atmosphere and the ocean, especially in coastal and high-latitude regions. This work is key to enhancing the capability of future GCMs to simulate coastal changes and extreme events.