Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 24). / In this thesis, spontaneous tropical cyclogenesis occurring in a cloud-resolving numerical model is studied. The model environment is one of radiative convective-equilibrium on an f-plane with doubly periodic boundary conditions and constant sea surface temperature. While a variety of initial conditions may exhibit spontaneous tropical cyclogenesis, this study focuses on one. Using assumptions of axisymmetry for the growing disturbance and focusing on the large scale processes, fields were created for a number of thermodynamic variables along constant height surfaces and as azimuthal means plotted against height. The tropical cyclone is hypothesized to develop in three steps. First, convective aggregation creates regions of high moist static energy, and regions of cold dry air. Importantly, a deep moist column is created which provides a perfect environment the developing storm. In the second step, mid-level cyclone intensification, a mid-level cold core cyclone develops in the deep moist region, and benefits from moist static energy and potential vorticity fluxes from the upper troposphere. Exhibiting anticyclonic convergent flow, the upper troposphere is an unlikely source for the mid-level disturbance, while convective downdrafts and divergent surface flow hinder energy transport from the ocean to the growing system. In fact, a cold surface anticyclone exists near the center for much of the second step. It is not until potential vorticity anomalies advect down to the surface that the final step, low-level cyclone intensification, creates a classical hurricane structure. Potential vorticity advection stimulates cyclonic flow at the surface, extinguishing the surface anticyclone, and thereby linking the mid-level disturbance to the oceanic energy source. While like some cold core cyclones previously studied, the anticyclone as an energy source is unique to this spontaneous case. / by Paul M. Hoffman. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 51-55). / Recently acquired altimetry data from laser altimeters are used to assess the morphometry of impact craters. Data acquired by the Mercury Laser Altimeter on the MESSENGER spacecraft are used to measure the depths and diameters of 537 craters at the high northern latitudes on Mercury, including 42 polar-deposit-hosting craters (PDCs) which host material that is bright to earth-based radar observations. A comparative analysis suggests that the radar-bright material forms a thin (< 20 m) layer emplaced preferentially in comparatively young craters, contradicting an earlier morphometric study that indicated that PDCs contained a thick layer of water ice and dust. Topographic datasets from the lunar surface, collected by the Lunar Orbiter Laser Altimeter onboard the LRO spacecraft, are also used to evaluate the morphometry of 1,356 lunar craters. We study the morphologic change between the simple and complex crater regime, a manifestation of the transition between gravity-dominated and strength-dominated impact-forming processes, on the Moon and Mercury. The Moons transition diameter is near 16 km, in line with previous studies, while Mercurys is near 8 km, 2 km smaller than previously determined. The onset of gravity-dominated mechanisms scales inversely with gravity, which explains why Mercurys transition diameter is approximately half of the Moons. / by Matthieu Jean Talpe. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 52-56). / Twelve bedrock samples were collected from Ticino, Switzerland and Northern Italy for thermochronological studies using the (U-Th)/He technique on zircon and apatite and fission track on subset of zircons. Nine samples were collected from the Lepontine Dome, north of the Insubric Line, six of which were in an approximate vertical, or elevation, transect. Three samples were also taken in a vertical transect from the Southern Alps, south of the Insubric Line. (U-Th)/He Zircon dates from north of the Insubric line ranged from 7 to 14 Ma, and indicate an approximate exhumation rate for the region of 1000 m/Ma. U-Th/He zircon dates from south of the Insubric Line ranged from 100 to 180 Ma, with one reliable apatite date of 23 Ma. These data lead to an approximate exhumation rate of 20 m/Ma in the south with rates increasing to about 150 m/Ma since 23 Ma. Thus very different exhumation histories can be inferred north and south of the Insubric Line, with the north side showing much younger dates and a higher exhumation rate related to continued orogenic activity, whereas to the south, there are lower rates and older dates indicating little to no orogenic activity until ca 23 Ma. / by Jessica R. Stanley. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / 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 (p. 269-304). / The endeavor to characterize terrestrial exoplanets warrants the study of chemistry in their atmospheres. Here I present a comprehensive one-dimensional photochemistry-thermochemistry model developed from the ground up for terrestrial exoplanet atmospheres. With modern numerical algorithms, the model has desirable features for exoplanet exploration, notably the capacity to treat both thin and thick atmospheres ranging from reducing to oxidizing, and to find steady-state solutions starting from any reasonable initial conditions. These features make the model the first photochemistry-thermochemistry model applicable for non-hydrogen-dominated thick atmospheres on terrestrial exoplanets. Using the photochemistry model, I explore the compositions of thin atmospheres on terrestrial exoplanets controlled by surface emission and deposition of gases. Highlights of my findings are: (1) oxygen and ozone may build up in 1-bar CO2 atmospheres to levels that have conventionally been accepted as unique signatures of life, if there is no surface emission of reducing gases; (2) volcanic carbon compounds (CH4 and CO2) are likely to be abundant in terrestrial exoplanet atmospheres; but volcanic sulfur compounds (H2S and SO2) are chemically short-lived and therefore cannot accumulate in virtually any types of terrestrial exoplanet atmospheres. Also using the photochemistry model, I explore the ranges of molecular compositions of thick atmospheres on terrestrial exoplanets. I find that carbon has to be in the form of CO2 in a H2-depleted water-dominated atmosphere, and that the preferred loss of light elements from an oxygen-poor and carbon-rich atmosphere leads to formation of unsaturated hydrocarbons (C2H2 and C2H4). These results imply that chemical stability has to be taken into account when interpreting the spectrum of a super Earth/mini Neptune like GJ 1214b. Another intriguing category of terrestrial exoplanets is bare-rock exoplanets. I present the first theoretical framework to compute disk-integrated spectrum from a bare-rock exoplanet, taking into account the reflectivity and emissivity of solid minerals on the surface. I find that silicate surfaces lead to prominent spectral features in the 8 - 13 [mu]m range, detectable by mid-infrared spectroscopy using transit. Therefore transit spectroscopy is an independent method to confirm the rocky nature of an exoplanet. / by Renyu Hu. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (leaves 84-88). / Atmospheric studies of halogenated organics have centered on long lived halocarbons due to their effect on stratospheric ozone. Now that controls have been put in place to curb emissions of longer lived halocarbons through the Montreal Protocol, and speculation about the safety of many short-lived chlorinated organic molecules has been raised, there has been more consideration given to the efforts aimed at determining the levels of human exposure to all types of halogenated organics. Most previous studies of reactive chlorine compounds have focused solely on quantifying their ambient levels in urban and rural regions. However, for many of these organo-chlorine molecules a detailed knowledge of emissions levels, transport, and final environmental disposition still does not exist. The present work was designed to aid in understanding the emissions patterns for several reactive halogenated organic compounds including trichloromethane (chloroform, CHCl3), trichloroethene (TCE, CHClCCl2), and tetrachloroethene (perchloroethylene, CCl2CCl2). A high temporal frequency (hourly) measurement campaign in Nahant, Massachusetts (approximately 10 km. northeast of Boston) provided automated gas-chromatographic measurements for these species as well as the somewhat more stable 1,1,1 trichloroethane (methyl chloroform, CH3CCl3). Cryogenic preconcentrations, daily calibrations, and weekly linearity tests insure high precision (</= 5%) measurements using electron capture detection. Calibration gases used for these tests, initially manufactured at MIT, have been corrected by intercomparison with gas standards used by the AGAGE program (produced at Scripps Institution of Oceanography) as well as those used at the National Center for Atmospheric Research. The absolute accuracy of our corrected MIT standard is estimated to be 10%. Over 12,000 measurements of the selected species were made between March, 1998 and January, 1999. These data show wide variability for the shortest lived species ranging from our detection limits (4.5 ppt for trichloroethene, 4.2 ppt for tetrachloroethene, and 7.8 ppt for trichloromethane) up to several hundred ppt during periods of local pollution. Data analysis combines the measurements with back trajectory information obtained from the HYSPLIT4 model (HYbrid Single-Particle Lagrangian Integrated Trajectory model, NOAA Air Resources Laboratory, Silver Springs, Maryland). Using a Kalman filter inverse method and an analytical solution of the continuity equation to estimate the effect of diffusion, we calculate the surface emissions for the selected species necessary to optimally match the observations. These emissions are compared with the estimates determined by the Reactive Chlorine Emissions Inventory (RCEI) working group of the IGAC (International Global Atmospheric Chemistry Program) Global Emissions Inventory Activity (GEIA). RCEI estimates are primarily derived from point source emissions in the US Toxic Release Inventory (TRI) and population-based distribution of residual national consumption from sales records. The new emissions scenarios computed here provide an observation-based assessment for comparison with the emissions inventories produced by RCEI for the northeastern United States and southeastern Canada. Results are statistically consistent with the RCEI estimates given the currently rough accuracy (±47-67%) achievable through this observation-based technique. We note, however, that the best estimate of corrections factors for land-based grid cells presented here indicate that the RCEI emissions for trichloroethene and tetrachloroethene need to be increased by a factor of ~2 to explain the observations. Only anthropogenic sources of trichloromethane were gridded in the initial (RCEI) inventory representing roughly 11% of estimated global emissions. We find that these emissions are, as expected, too low to explain the observations and that a land-based correction factor ~12 is required to produce emissions estimates that are consistent with natural sources (e.g. soil emissions). We also note that very large correction factors are calculated over the oceanic grid cells resulting in revised emissions estimates of the same order of magnitude as many land-based grid cells, consistent with a large oceanic source for this compound inferred from oceanic observations. The 47-67% uncertainty in the estimates of emissions correction factors increases with distance from the observation site due to both the increase in trajectory error as a function of total trajectory length and the decrease in the number of trajectories which have passed through a particular grid cell as one moves further from the observation site. These and other sources of uncertainty can be reduced by providing a realistic weighting of each trajectory's accuracy thus minimizing the impact of the trajectories which are likely to be most inaccurate, increasing the total number of measurements so that all grid cells have greater trajectory coverage, and improving estimates of the effective mixed layer height. / by Gary Kleiman. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990. / Includes bibliographical references. / by Paula G. Coble. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000. / Includes bibliographical references (leaves 43-44). / The changing configurations of continents due to plate tectonics is thought to be responsible for some of the variation in climate over the last 600 Ma. Different topological constraints on the oceans may affect their ability to transport heat poleward and change the equilibrium pole-equator temperature of Earth. An ocean model was run for three simple continental geometries to determine the effect of land distribution on the heat transport capacity and pole-equator temperature gradient of the ocean. The first configuration, a circle of land centered over the south pole, meant to resemble Earth at 600 Ma, produces a haline mode of convection in which water sinks in the subtropics. The ocean in this mode has a high pole-equator temperature gradient and low levels of heat transport. The second configuration, a strip of land extending between the north and south poles, resembles the land of the Permian 250 Ma. This configuration with the same atmospheric forcing produces a thermal mode of circulation, similar to the modern North Atlantic, in which surface water sinks at the poles. The ocean in this mode has a lower pole-equator temperature gradient and higher levels of poleward ocean heat transport. A third configuration, similar to the second but with an equatorial ocean passageway, resembles the mid-Cretaceous. This configuration also produces a thermal mode and has slightly higher levels of heat transport than the second model. This research suggests that continental geometry could have played an important role in determining the pole-equator temperature gradient and the levels of ocean heat transport in the past. / by Lorraine Lisiecki. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references. / The main objective of the research presented in this thesis is to improve our understanding for the evolution of the upper mantle beneath East Asia and the Tibetan Plateau through high resolution P-wave tomography. The approach to high resolution tomography is based on (i) the combined use of a large range of different types of seismic data, (ii) the use of approximate finite frequency sensitivity kernels to account for difference in measurement technique and frequency content of the data, (iii) the use of an irregular grid with cell-size adapted to sampling density, and (iv) the use of a priori information, e.g., on crustal structure from receiver function analysis. I construct a multi-scale and high resolution seismic tomography model of the upper mantle structure beneath East Asia and the Tibetan Plateau. The new model reveals that the mantle structure associated with the Indian subduction varies considerably along the strike of the collision zone. From west to east, the dip angle of Indian subduction increases and the distance over which the plate underthrusts the Tibetan Plateau decreases. Oblique subduction and changes of dip angle in the central part of the collision zone may cause and determine the location of the north-south trending normal faults in central Tibet. The eastward retreating slabs of western Pacific and Philippine plates are deflected in the transition zone beneath the Korea, Japan Sea, and East China. Some of Mesozoic subducted slabs have reached as far west as 1100E longitude under the Yangtze Craton, which might have resulted from the Eocene subduction at the South China and Japan trenches. / (cont.) Precambrian continental roots under Ordos block and Sichuan Basin, which extend to 250-300 km depth, may form a boundary of transition in tectonic regimes from the India-Eurasia collision control in the southwest to Pacific, Philippine Sea, and Java-Sumatra subductions control in the east and southeast. I conclude that the (direct) influence of the India-Eurasia collision on the tectonic evolution of East Asia may be confined to the Tibetan plateau and vicinity, whereas the tectonic development of a large area east and southeast of Ordos, Sichuan and Burma is driven by the stress field and 3-D upper mantle processes associated with subductions of Pacific, Philippine Sea, and Indo-Australia plates. / by Chang Li. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 227-234). / The thesis consists of five studies relating impact processes to the evolution of planetary interiors as well as impact structures on planetary surfaces. Chapter 2 is concerned with developing methods for estimating the amount of heat deposited deep in terrestrial mantles by large impacts. Chapter 3 makes use of these results to compute the consequences of impact-related thermal buoyancy perturbations in numerical models of subsolidus convection. Among the important results of this work is a relation for the time-scale on which a buoyancy anomaly flattens and spreads before it is halted by convective downflows, as well as a condition that indicates for what perturbation magnitudes and Rayleigh numbers the flow is significantly slowed at a global scale. Chapter 4 describes a structural model of Endurance Crater in Meridiani Planum on Mars, which is constrained by observations gathered by the MER-B Opportunity rover. These results reveal new insights about the planform shape of the crater excavation flow, as well as the connection between crater shape and pre-existing structures in target materials. The study presented in chapter 5 relates the planimetric shape of simple impact craters on Mars (D < 5 km) to the geological targets in which they form, as well as rim diameter. Planform crater shape is characterized by a suite of morphometric parameters, including Fourier harmonic amplitudes and phase angles, as well as measures of deviation from radial symmetry and convexity. / (cont.) In addition to finding the morphometric dependence on target properties, this work has illuminated prominent transitions between different cratering regimes, and contains a measure of the global distribution of planform elongation azimuths - which may relate to impact azimuth and provide an estimate of Mars' past obliquity variations. Finally, Chapter 6 describes a stochastic-kinematic model of the interaction between the excavation front and fractures in the target, which replicates many of the observations obtained in Chapter 5. / by Wesley Andrés Watters. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Folded map in pocket at back of thesis. / Bibliography: leaves 369-388. / by David Christian Gerlach. / Ph.D.