Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003. / Includes bibliographical references (leaves 278-286). / This dissertation made three contributions to numerical simulation and borehole acoustic logging. The first one is a novel finite difference time domain algorithm that features non- uniform grid, wavelet-based difference operator and anisotropic perfectly matched layer. This algorithm reduces numerical reflections and wave distortions introduced by grid change to a minimum by sampling the physical space with gradually varying mesh. By coordinate stretching, the algorithm discretizes the physical space with variable grid, while solving the wave equation on a uniform mesh. That approach helps retain the advantages pertaining to uniform mesh. Further improvement in efficiency is achieved without losing accuracy by the development of a wavelet-based difference operator. By using a family of compactly supported wavelet function, the wavelet- based finite difference time domain algorithm allows less grid point per wavelength. Coordinate stretching is also employed in deriving an anisotropic perfectly matched layer, superior to currently available perfectly matched layer formulation which re quires field splitting, a process that results in more computer memory requirement for the storage of extra variables. Validations of the algorithm include comparison with analytical solutions, uniform grid FDTD solutions and discrete wavenumber results. The second contribution is a time domain investigation of wave propagations in the logging while drilling situation. Logging while drilling is an emerging downhole acoustic acquisition method. The investigation is focused on soft formations where formation shear velocity is slower than borehole fluid velocity, because shear velocity measurement, one of the key measurements that acoustic logging is designed / (cont.) to acquire, is the most problematic in soft formations. Special attention is paid to mode excitations, with respect to frequencies, tool positions and source types, in the hope to shed some light on some highly debated questions regarding tool design and data interpretation. The stretched grid finite difference algorithm is applied. The third contribution is the development of an inversion method to estimate stress magnitudes and directions from borehole acoustic measurements. It is predicted in theory that a crossover in flexural dispersion is an indicator of stress-induced anisotropy dominating over other sources of intrinsic anisotropy. The prediction is subsequently verified in a scaled-borehole experiment. We are the first ones that observe flexural dispersion crossover in field data. Using the flexural crossover as a stress signature on the borehole acoustic data, we are able to isolate stressed zones. The maximum horizontal stress direction coincides with the polarization direction of far field fast shear. The stress magnitude is related to velocity changes in the stressed state from the zero stress or hydrostatically balanced state, through a perturbation theory developed in the late 1990's. Stress directions estimated in this dissertation are consistent with focal mechanism and borehole breakout data present in the world stress map database. / by Xiaojun Huang. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (leaf 34). / The self-potential method (SP) of geophysical surveying has been widely used in environmental and engineering applications, primarily for rough but inexpensive assessment of subsurface flow of fluids, heat, or ions. In this project, the SP method was employed to study the activity at an environmental cleanup site at the Massachusetts Military Reservation. At the leading (down-gradient) edge of the CS-4 groundwater contamination plume, a fence of pump-and-treat extraction wells has been operating in an effort to contain the plume migration. To help gauge the effectiveness of the pump-and-treat technique, it is useful to delineate the resultant water flow and to compare it to the extent and diffusion gradient of the contaminant plume. In the survey conducted for this project, SP measurements were taken along the fence of extraction wells, while they were in operation, and during a period in which the well pumps were shut off. Spatial and temporal variations in the SP measurements are analyzed. Some possible explanations are proposed to account for the observed features and changes over time. While the results are not entirely conclusive, they suggest that water flow provides only a modest contribution to the total observed SP anomaly. / by Danny Fain. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (p. 108-109). / by Sarah Elizabeth Herbelin. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Includes bibliographical references (leaves 55-56). / by Hafiz Jaman Alshammery. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (leaves 57-64). / I investigate the hypothesis that the young and smooth surface of the Martian northern hemisphere is due to volcanic resurfacing driven by degree-one convection. I implement a batch melting process in a finite element convection model and run numerical experiments to quantify the melt fraction, timing of melting, and timing of the onset of degree-one convection. All models include a stratified viscosity to induce degree-one flow. To assure that the model's result is robust I vary the model's initial conditions, core-mantle boundary temperature and radius, and the thickness of the lithospheric lid. Long-wavelength convection is a consistent result of the viscosity stratification, and degree-one occurs in one third of the numerical experiments. I compare the melt fraction and onset of degree-one convection to the geological evidence from Martian orbiters, rovers, and meteorites. Good agreement is found between the numerical models and geological evidence, so this model suggests that volcanism driven by degree-one convection may play a significant role in the young age of the northern hemisphere of Mars. / by P. James Dennedy-Frank. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (p. 88-90). / by Nicolas Fiszman. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 96-99). / This work seeks to improve understanding of atmospheres in radiative-convective equilibrium. We use two types of idealized, dry radiative-convective models. The first type of model resembles Rayleigh-Benard convection, except that thermal radiative transfer is included. This type of system can be investigated in the laboratory. The second type of model is a more faithful representation of the earth's atmosphere. In this model, the temperature at the upper boundary is left unspecified, unlike the case of Rayleigh-Benard convection. For these two types of radiative-convective models, we perform various theoretical and numerical analyses of the stability properties, and various analyses of the weakly nonlinear convecting state. We prove that in these models, convection arises as monotonically growing cells, not as an oscillatory instability. That is, we prove exchange of stabilities. We investigate the linear stability modes. We find that in most cases, the linear stability threshold can be described approximately or exactly in terms of a radiative Rayleigh number. The radiative Rayleigh numbers used are like the classical Rayleigh number but with modified temperature and thermal diffusivity scales. Inspection of the radiative Rayleigh numbers reveals how various external parameters, such as the net incoming solar radiation or infrared opacity, affect the stability properties. We use the energy method to find a threshold value of a stability parameter below which all disturbances to the radiative equilibrium state, regardless of magnitude, decay. For those radiative equilibrium states which have a linear temperature profile, the energy stability threshold coincides with the linear stability threshold, thereby ruling out the possibility of subcritical instabilities. When the temperature profile is nonlinear, the energy stability profile lies below the linear stability threshold. We study weakly nonlinear convection in the atmospheric radiative-convective model via the mean field approximation. In contrast to the stability threshold, the vertical convective heat flux in the weakly nonlinear convecting state turns out to be little affected by the values of viscosity, thermal diffusivity, or radiative damping. However, the convective heat flux is strongly affected by the net incoming solar radiation and the optical depth. We formulate scaling laws for vertical convective heat flux, vertical velocity, and temperature perturbations. These scales extend the Prandtl scales to higher altitudes. / by Vincent Edwin Larson. / Ph.D.

Thesis: Ph. D. in Atmospheric Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 141-148). / Atmospheric nitrous oxide (N₂O) significantly impacts Earth's climate due to its dual role as an inert potent greenhouse gas in the troposphere and as a reactive source of ozone-destroying nitrogen oxides in the stratosphere. Global atmospheric concentrations of N₂O, produced by natural and anthropogenic processes, continue to rise due to increases in emissions linked to human activity. The understanding of the impact of this gas is incomplete as there remain significant uncertainties in its global budget. The experiment described in this thesis, in which a global chemical transport model (MOZART-4), a fine-scale regional Lagrangian model (NAME), and new high-frequency atmospheric observations are combined, shows that uncertainty in N₂O emissions estimates can be reduced in areas with continuous monitoring of N₂O mole fraction and site-specific isotopic ratios. Due to unique heavy-atom (15N and 18O) isotopic substitutions made by different N₂O sources, the measurement of N₂O isotopic ratios in ambient air can help identify the distribution and magnitude of distinct sources. The new Stheno-TILDAS continuous wave laser spectroscopy instrument developed at MIT, recently installed at the Mace Head Atmospheric Research Station in western Ireland, can produce high-frequency timelines of atmospheric N₂O isotopic ratios that can be compared to contemporaneous trends in correlative trace gas mole fractions and NAME-based statistical distributions of the origin of air sampled at the station. This combination leads to apportionment of the relative contribution from five major N₂O sectors in the European region (agriculture, oceans, natural soils, industry, and biomass burning) plus well-mixed air transported from long distances to the atmospheric N₂O measured at Mace Head. Bayesian inverse modeling methods that compare N₂O mole fraction and isotopic ratio observations at Mace Head and at Diibendorf, Switzerland to simulated conditions produced using NAME and MOZART-4 lead to an optimized set of source-specific N₂O emissions estimates in the NAME Europe domain. Notably, this inverse modeling experiment leads to a significant decrease in uncertainty in summertime emissions for the four largest sectors in Europe, and shows that industrial and agricultural N₂O emissions in Europe are underestimated in inventories such as EDGAR v4.3.2. This experiment sets up future work that will be able to help constrain global estimates of N₂O emissions once additional isotopic observations are made in other global locations and integrated into the NAME-MOZART inverse modeling framework described in this thesis. / by Michael James McClellan. / Ph. D. in Atmospheric Science

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (p. 192-194). / by Margaretha M. Eckhardt. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 163-167. / by Michel M. Verstraete. / Sc.D.