Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 88-93). / The atmospheric component of the global biogeochemical mercury cycle was studied to determine the mechanisms behind diurnal trends and amplitudes in elemental and reactive gaseous mercury concentrations over terrestrial environments. This analysis was done using the 3D GEOS-Chem chemical transport model and the creation of a simple one-box model. Mercury is a significant neurotoxin for humans and other species that has been addressed in the policy realm on both national and international levels. Being able to model atmospheric mercury processes correctly is an important part of regulation and policy drafting. GEOS-Chem model results were compared with Weiss-Penzias et al. [2009] measurements for three Nevada, USA sites. The magnitude of elemental mercury concentrations differed by 0.07-0.2 ng/m3 , with GEOS-Chem underestimating concentrations due to an under-representation of mercury emissions at naturally enriched sites. The amplitude of reactive gaseous mercury diurnal variations differed by a factor of 3-4, with GEOS-Chem underestimating the diurnal trend. Based on the diurnal nature of this error, it is hypothesized that GEOS-Chem under represents the magnitude of elemental mercury emissions, the amount of oxidation occurring in the atmosphere, and the scale of entrainment from the free troposphere. / by Anastasia F. Maheras. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 108-113. / by Rui Vasques de Melo Ponte. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 55-57). / Dating back to 3.5 Gya, stromatolites, which are composed of laminated and lithified carbonate rock, may contain the earliest records of phototaxis, photosynthesis, and oxygenation of the environment. The reconstruction of the co-evolution of biology and the environment using stromatolites depends on the ability to recognize macroscopic shapes that arise uniquely as a consequence of microbial processes. Our investigation aims to understand the biological factors in the formation of conical structures and stromatolites. To elucidate the role of the cyanobacteria, we enrich cyanobacteria from modern hot-spring communities of cone-forming microbes and subsequently test how the formation of conical structures depends on individual strains of the community. In our analysis, we augment morphological identification by genomic analyses of the 16S ribosomal DNA. Through a combination of mixing isolated heterotrophic bacteria and enriched filamentous cyanobacteria communities, we find that heterotrophic bacteria are a determinative factor in the formation and morphology of conical structures. Further, our experiments show the mere presence of a thin, filamentous cone-forming cyanobacteria phenotype is not a sufficient condition for cone formation. / by Alexander Joseph Evans. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Page 231 blank. / Includes bibliographical references (p. 221-230). / In this thesis, we investigate atmospheric water vapor transport through a distinct synoptic phenomenon, namely, the Tropospheric River (TR), which is a local filamentary structure on a daily map of vertically integrated moisture flux. Firstly, an automated procedure for identifying and tracking these rivers (named TRICKS, i.e., the Tropospheric River Identifying and traCKing Scheme) is described and its performance is evaluated. This procedure enables the maxima of moisture flux (so-called TR cores) to be detected and accurately located. The relationships among the adjacent TR cores are then evaluated to construct the axes of rivers. A river is tracked from birth to termination and its life cycle properties are recorded, thus allowing various statistics of TR distributions and movements to be estimated. All these stages of the scheme are performed without intervention once a number of governing constants have been decided upon. We then apply the scheme to the vertically integrated moisture flux calculated from 43 years of 6-hourly NCEP/NCAR reanalyses and present a climatology of mean TR behavior. On average, there are 4 - 5 rivers per analysis in the Northern Hemisphere and 5 in the Southern Hemisphere. Northern Hemisphere TRs form and intensify near the eastern seaboards of Asia and North America. They move eastward and poleward during their lives before weakening in the two principal graveyards: over the Gulf of Alaska and the region to the southeast of Greenland. In comparison, Southern Hemisphere TRs are more evenly distributed and tend to form in a band extending from the southeast coast of South America into the Atlantic, across the Indian Ocean, and throughout much of middle latitudes of the Pacific sector. / (cont.) The corresponding genesis regions are also found to be adjacent to (or slightly equatorward to) the maximum SST gradients in these regions. It appears that both TR genesis and termination maxima tend to be displaced near the upstream equatorward flanks of cyclogenesis and lysis maxima. We suggest that the TR formation and termination could be a leading predictor for the occurrence and decaying of extratropical cyclones. TR axis length appears to be longer during the warmer season and in the Southern Hemisphere. The distance traveled by TR systems shows a broad distribution and a sizeable fraction (-25%) of systems travel in excess of 3000 km. One unique feature is that although TRs occur very actively over the Indian ocean sector with highly densed tracks, large translational speeds, and intensities, they contribute little to meridional water vapor transport, while the reverse situation can be found in the South Pacific where southward transport is sometimes comparable to those over or off the east coast of South America. The rivers seem to account for a substantial fraction of the total meridional moisture transport in both middle and subtropical regions. Finally, we complete the TR climatology with an analysis of the variability and trends exhibited by many aspects of rivers during the 43-year period. The annual average number of TRs per analysis has undergone an overall increase during the last couple of decades and is more significant in the Southern Hemisphere. The greatest increases occur in the 50⁰-30⁰S and 50⁰-70⁰N belts ... / by Yuanlong Hu. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009. / Cataloged from PDF version of thesis. Original thesis missing page 55. / Includes bibliographical references (pages 71-72). / Air traffic managers need up to date nowcast information over the entire CONUS for efficient operations in the National Airspace System. In areas of degraded or no radar coverage, cloud-to-ground lightning (provided by the National Lightning Detection Network) can provide valuable information through the creation of proxy vertically integrated liquid (VIL) and echo tops (ET). To develop these lightning-VIL and lightning-ET relationships, analysis of the lightning and radar data was done in "climate zones" throughout the CONUS, due to the potential for different lightning behavior in different areas of the country. After a quantile analysis revealed differences in the data between zones, lightning-VIL. and lightning-ET relationships were developed using a probability matching method for a baseline relationship (all climate zones) and for each individual climate zone. The potential benefits of the inclusion of each zone were analyzed through a bootstrap testing of the proxy VIL and proxy ET models, and performance was assessed using a system of binary scoring. For a given lightning flash rate, VIL values in the Mid-Latitude Land West zone were considerably lower than in other zones. The Mid-Latitude Land West zone also showed a noticeable improvement in the performance of the proxy VIL model. For a given lightning flash rate, ET values in the Mid-Latitude Water zone were considerably lower than in other zones. The Mid-Latitude Water zone appeared to provide a statistical improvement in the proxy ET model, but because of a lack of data in this zone on the days chosen for model testing, this improvement was not noticeable in the overall performance of the proxy ET model and needs to be investigated further. / by Erin B. Munsell. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 235-251). / This dissertation presents data processing techniques relevant to the acquisition, modeling, and inversion of self-potential data. The primary goal is to facilitate the interpretation of self-potentials in terms of the underlying mechanisms that generate the measured signal. The central component of this work describes a methodology for inverting self-potential data to recover the three-dimensional distribution of causative sources in the earth. This approach is general in that it is not specific to a particular forcing mechanism, and is therefore applicable to a wide variety of problems. Self-potential source inversion is formulated as a linear problem by seeking the distribution of source amplitudes within a discretized model that satisfies the measured data. One complicating factor is that the potentials are a function of the earth resistivity structure and the unknown sources. The influence of imperfect resistivity information in the inverse problem is derived, and illustrated through several synthetic examples. Source inversion is an ill-posed and non-unique problem, which is addressed by incorporating model regularization into the inverse problem. A non-traditional regularization method, termed "minimum support," is utilized to recover a spatially compact source model rather than one that satisfies more commonly used smoothness constraints. Spatial compactness is often an appropriate form of prior information for the inverse source problem. Minimum support regularization makes the inverse problem non-linear, and therefore requires an iterative solution technique similar to iteratively re-weighted least squares (IRLS) methods. / (cont.) Synthetic and field data examples are studied to illustrate the efficacy of this method and the influence of noise, with applications to hydrogeologic and electrochemical self-potential source mechanisms. Finally, a novel technique for pre-processing self-potential data collected with arbitrarily complicated survey geometries is presented. This approach overcomes the inability of traditional processing methods to produce a unique map of the potential field when multiple lines of data form interconnected loops. The data are processed simultaneously to minimize mis-ties on a survey-wide basis using either an 12 or 11 measure of misfit, and simplifies to traditional methods in the absence of survey complexity. The 11 measure requires IRLS solution methods, but is more reliable in the presence of data outliers. / by Burke J. Minsley. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis primarily investigates how the conditions of crystallization affect the chemical evolution of magmas. A major focus is the effect of water on the stability of mineral phases, and how this affects both the differentiation of magmas and the modification of the upper mantle by hydrous fluid release during subduction. Chapter 1 models the crystallization of the asteroid Vesta, which melted almost completely during the early history of the solar system. Chemical modeling of the crystallization of this water-free "magma ocean" shows that the howardite-eucrite- diogenite (HED) meteorite suite that makes up Vesta's crust was likely formed by a combination of fractional crystallization and magmatic recharge from the asteroid's deeper interior. Chapter 2 investigates the sodium-rich tuffs deposited during the ~75 kyr eruption of Newberry Volcano, Oregon. Experiments at different pressures and water contents show that the magma differentiated in the shallow crust in the presence of 1-2 wt.% water. These conditions produce characteristic magma compositions that are also observed in many other parts of the Cascade arc and further afield. Chapter 3 tests the hypothesis that the tonalities, trondhjemites, and granodiorites (TTG) that make up much of the Archean crust may have been generated by fractional crystallization. Experiments show that fractional crystallization at modest water contents (1-2 wt.%) and high pressures (>/= 12 kbar) may have played an important role in the evolution of the Archean crust. Chapter 4 provides experimental constraints on the stability and composition of the hydrous mineral amphibole in the Earth's lithosphere. The results are used to develop a new thermobarometer for metasomatized peridotites, and provide improved constraints on the water storage capacity of the Earth's upper mantle and the conditions under which amphibole breaks down. Collectively, these studies show and help to quantify the important roles of fractional crystallization and water in modifying the crust and upper mantle of rocky planets. / by Benjamin Ehrlich Mandler. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaf 53. / by Richard A. Wagner, Jr. / M.S.

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 267-274). / A wide range of problems in seismology have a localized nature. Examples include inversion for time-lapse change, salt boundary position and Amplitude or Phase Versus Angle (AVA/PVA). With increasing computational power, many inversion procedures have transitioned away from forward models with simplified physics and now simulate synthetic wavefields on a model representation of the Earth. These simulated wavefields form the basis for the model updates in the inversion. Usually these wavefields are simulated on the entire computational model, even though the region of interest and the associated updates of the computational model are localized. In this thesis I explore ways of making use of the localized nature of the inversion by limiting the wavefield generation to the region of interest. This shrinking of the computational domain leads to faster solutions, reducing the time between the start and finish of the local inversion. This shorter turn-around time facilitates decision making and improves the interactivity of the inversion procedure. I first introduce a frequency domain local solver which can generate exactly the same wavefields as a full domain solver. I then apply this local solver to both a time-lapse problem and to salt boundary inversion. I then take a step back and look at time-lapse inversion outside the scope of local solvers. By looking at differences in the Full Waveform Inversion (FWI) gradient obtained from baseline and monitor datasets I compute a confidence map of locations likely to contain time-lapse change. This confidence map is then used to regularize a joint inversion for both the baseline and monitor datasets. I compare this methodology to other existing time-lapse algorithms on a synthetic North Sea model. In this study I notice the importance of post-critical reflections and become aware of their potential for reservoir characterization. Motivated by this observation I introduce a local solver for simulating elastic reflections in a region of interest. These elastic reflections can then be used for AVA and PVA to for instance invert for reservoir characteristics. The wavefield is efficiently propagated through the overburden using precomputed acoustic Green's functions obtained from a cheap acoustic solver. / by Lucas Abraham (Bram) Willemsen / Ph. D. in Geophysics

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Bibliography: leaves 100-102. / by John McClements Lambie. / M.S.