2016 EAPS Senior Thesis Presentations

Helen Hill | EAPS News
Friday, June 3, 2016

Each year, graduating seniors majoring in EAPS present a thesis in completion of their Bachelor of Science Degree. This year we had a class of eight students specializing in areas across the earth, atmospheric and planetary sciences.

Analysis of Pluto’s Lightcurve to Detect Volatile Transport
Megan L. Mansfield (advisor Dr. Amanda Bosh)

Research: A model was created to synthesize lightcurves of Pluto, given the viewing geometry and surface albedo distribution. Using an initial surface albedo distribution based on images taken by New Horizons, changes in the lightcurve mean magnitudes and amplitudes over time were compared to the smallest magnitude changes detectable by a variety of telescopes. The model predicts that a 6.5-meter telescope, such as Magellan, would be able to detect magnitude changes due to a shift in viewing geometry over one year to a three-sigma level of certainty. Additionally, telescopes as small as 2 meters in diameter would be able to detect changes over timescales of less than three years. Beyond purely geometric changes, Pluto's brightness will also respond to changes in surface albedo. The model can be compared to future observations to estimate how much surface albedo change is necessary to produce the observed lightcurves, and can therefore be used to link observational data to physical changes on Pluto's surface and the methods of volatile transport responsible for those changes.

What's Next: "I will be attending graduate school at the University of Chicago in the Department of Geophysical Sciences."


Analysis of Magnetic Activity Cycles in Solar Analogs Using Solar – Stellar Spectrograph Data
Duy-Ahn N. Doan (advisor Dr. Amanda Bosh)

Research: The Solar-Stellar Spectrograph (SSS) Project made frequent observations of 30 – 50 Sun-like stars to address a wide variety of questions regarding the nature of stellar magnetic activity cycles. The magnetic activity cycles of 18 stars in the Solar – Stellar Spectrograph (SSS) project are analyzed using the Lomb – Scargle method of least-squares spectral analysis. Resulting periodograms reveal that most stars may have one or two dominant magnetic cycles, with periods ranging from 2 years to 17 years. Most of the detected cycles have a false alarm probability (FAP) well below 10-3. The results for a number of stars are compared and confirmed with earlier observation by Mount Wilson Observatory’s project, published by Baliunas et. al. (1995). The results also agree with earlier findings by Saar and Brandenburg (2000) and Bohm-Vitense (2006) that stars generally follow two distinct sequences in the plot of stellar magnetic cycle periods as a function of rotational periods.

What's Next: "I will be pursuing a PhD in Astrophysics at Penn State."


Constraints on Passive Margin Escarpment Evolution from River Basin Reorganization in Brazil
Madison M. Douglas (advisor Prof. Taylor Perron)

Research: Escarpments are present on passive margins globally, but their evolution is poorly understood, with estimates of their retreat rates from the coast ranging from a kilometer per Myr to being stationary features. I investigate the modern evolution of the Brazilian escarpments by determining whether or not the river networks on either side of the escarpment are in equilibrium with each other using chi mapping, where a stationary escarpment would exhibit rivers at equilibrium (have the same value of chi at the ends of the tributaries) while a mobile escarpment would exhibit rivers at disequilibrium (different chi values at the tips of their tributaries). For comparison, I also compile cosmogenic 10Be erosion rates on either side of the escarpments from the existing literature, and use these to calculate current retreat rates of the escarpments, which fall between 4 and 40 m/Myr. I determine that chi mapping and cosmogenic erosion rates agree on the direction of escarpment movement, but disagree on the magnitude of the retreat rates. I also estimate the percentage of drainage area exchanged by stream capture as the escarpment drainage divide moves across the landscape. Using two different estimation methods, I find that less than 40% of drainage area is exchanged by stream capture, making divide migration the dominant mechanism for drainage basin reorganization. Therefore, the Brazilian escarpments have retreated up to 5 km since their formation during the Cretaceous rifting event, and this topographic retreat was driven by drainage basin disequilibrium resulting in divide migration.

What's Next: "I will be working for the US Geological Survey in Menlo Park, CA working on landslide hazard assessment and prediction, with fieldwork components around San Francisco and in Hawaii."


Using Machine Learning for Hydrocarbon Exploration in the Reconcavo Basin, Brazil
Elezhan Zhakiya (advisor Prof. Bradford Hager)

Research: This thesis is a result of the UROP I have done with Stephen Brown and Brad Hager that started over IAP of 2015. The main task was to figure out a method of using representing geological/structural variables correctly in Machine Learning, as well as using Machine Learning to combine data from multiple disciplines.

What's Next: "I will be pursuing my 5th year Master's with Prof. Bradford Hager"


Geochronological constraints on the Trinity diamictite in Newfoundland: Implications for Ediacaran glaciation
Judy Pu (advisors Prof. Kristin Bergmann, and Prof. Francis Macdonald, Harvard)

Research: The Avalon terrane in Newfoundland includes the Ediacaran Gaskiers Formation, which has been associated with a Snowball glaciation event and the rise of Ediacaran fauna. The complicated regional stratigraphy and lack of precise geochronological constraints has made it difficult to determine the relationship of the Gaskiers glaciation to these events. Recent recognition of a diamictite facies on the nearby Bonavista Peninsula correlative with the Gaskiers diamictite has allowed for new, high-precision geochronological constraints on the Gaskiers glaciation and constrains the duration of the event to less than 1 Myr. The short duration of this event makes it unlikely to have been a Snowball event, but further geochronological studies are needed to determine whether the Gaskiers glaciation was a discrete event or if it was a glacial maximum in a longer Ediacaran ice age.

What's Next: "I will be attending Harvard University for a PhD in Earth and Planetary Sciences."


Studying the Links Between Changes in the Variability and Seasonality of Temperature and Precipitation
Katrina L. Hui (advisor Prof. Paul O’Gorman)

Research: Recent studies suggested a linkage between Arctic amplification and reduced temperature variability in the mid and high latitudes, which may alleviate cold weather extremes (Screen, 2014; Schneider et. al., 2015). Arctic amplification may also modulate temperature seasonality, as sea ice loss may alter the land-ocean temperature contrast that dominates the spatial structure of temperature seasonality. This study investigates changes in variability and seasonality of temperature and precipitation to explore factors that contribute to their changes in the recent decades. The mean and subseasonal variance anomalies of temperature and precipitation are calculated over a 35-year period from 1979 to 2013 to search for trends. For temperature, warming trends amplified in the higher latitudes coincident with a significant decrease in variability in the mid and high latitudes were observed. For summer precipitation, a drying trend in the mean and a decreasing trend in variability were found in the midlatitudes. Fourier analysis of the seasonal cycles of temperature and precipitation revealed notable trends.  More specifically, Arctic sea ice loss may be linked to changes in seasonality of local temperature while Arctic amplification may have potentially influenced temperature seasonality in the mid and high latitude land regions. To determine whether the changes in temperature seasonality may have contributed to the observed reduction in temperature variability, analyses were performed by removing the phase trends from the temperature data using two methods. The phase trend-removed temperatures were found to have no prominent trends in variability. This suggests that changes in the temperature variance is primarily related to changes in temperature seasonality rather than changes in synoptic temperature variability. To study what affects the summer precipitation variability, the coefficient of variance, the ratio of variance to mean, which determines the shape of the mixed gamma probability distribution function (PDF) of precipitation was studied. It was found that the mean and variance of precipitation are generally proportional with a nearly constant ratio over time, suggesting that the shape of the precipitation PDF has not changed. Therefore changes in the precipitation variance in the midlatitudes could be simply explained by the change in the mean precipitation in the same region. Results suggest the importance of understanding temperature and precipitation seasonality changes to understanding changes in climate variability in the past and future.

What's Next: "I will be pursuing a Ph.D. in Environmental Science and Engineering at Caltech."


Mercury Emissions Inventories in the Lake Superior States
Elizabeth Berg (advisor Prof. Noelle Selin)

Research: The two main EPA inventories that track mercury emissions - the National Emissions Inventory (NEI) and Toxics Release Inventory (TRI) - often disagree. While the NEI numbers are more commonly used in research and modeling, TRI, which is compiled more frequently, is potentially also useful for studying emissions trends. For my thesis, I looked at recent mercury emissions data from both of these inventories for the states bordering Lake Superior. Dividing the data by sector, state and year, I tried to identify potential sources of bias or disagreement between the two inventories to determine how to best use each one.

What's Next: "I'll be working as a Policy Associate for Frontier Group, a nonprofit think-tank in Boston."


Records of Great Basin precipitation during MIS 11 from two Lehman Cave stalagmites
Ashling Neary (advisor Prof. David McGee)

Research: MIS 11 was long interglacial around 400,000 years ago, during which time there was pronounced high latitude warming in the Northern Hemisphere. My thesis aims to understand how precipitation in the Great Basin responded at this time. Trace element and stable isotope ratios are used to reconstruct precipitation records. Comparison with more recent records from the region has indicated that the Great Basin was exceptionally dry during MIS 11.

What's Next: "I will be pursuing a PhD at Brown University."



Special thanks, as always, to Jane Connor, EAPS' Lecturer II, for her work supporting and coaching this year's graduating class. Connor, who provides one-on-one writing and effective presentation support to EAPS undergraduates as well as undergraduates in other courses, holds a BA in English from Swarthmore College, and an MA in Languages, Literature and Communication, with an emphasis on Communication Theory, from Columbia University. 


Photo credit: Helen Hill

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