Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2000. / "August 1999." / Includes bibliographical references (p. 72-73). / Spectral methods are used to determine if there are any instances of narrow band oscillations in the climate signal over the past 1.4 million years. The study focuses on the suborbital and millennial-scale regime (~ 1 .5 - 20.0 kyr periodicities) at Site 980 and 983, two deep sea drill sites in the North Atlantic gathered by the Ocean Drilling Program in 1995. The study suggests one such narrow band oscillation in the sediment profile at Site 983, which is discussed from a variety of perspectives. Other questions addressed include a discussion of potential age-model inadequacies deriving from a potentially 'under-resolved' marine isotope map, as regards high-frequency climate variability. Site 983 has a 4-component sediment profile while Site 980 has a 2- component profile. This paper attempts to resolve the various independent inputs at Site 983 by the method described above. Four proxies have been used in this study; they are magnetic susceptibility, natural gamma, spectral reflectance, and GRAPE (Gamma Ray Attenuation Porosity Evaluator). These proxies are used to inform the millennial-scale issue by coherence methods and are also assessed to see which proxies may prove most useful in future high frequency research. Finally, a variety of mathematical and statistical methods have been employed including multi-taper analysis with different numbers of Slepian tapers, Singular Spectrum Analysis (SSA), noise background estimation methods (Mann and Lees, 1996), Akaike' s Information Criterion for AR(n) model fitting to a data set, and chi-square distribution confidence intervals. These various methods are discussed and evaluated according to their usefulness in sub-orbital research. / by Darrell Ardon Coles. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (leaves 336-353). / by Tanya Helen Furman. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001. / Includes bibliographical references (p. 214-223). / The chemistry of the stratosphere, in particular the balance between ozone production and loss, is very sensitive to transport into and out of the tropical stratosphere. There is a great deal of evidence that tropical air remains relatively isolated from extratropical air over timescales that are long compared to typical midlatitude mixing timescales. However, there are significant questions regarding the extent to which the tropics may be considered isolated, the mechanisms and variability of this isolation, and the implications of tropical isolation for global-scale transport. We address some of these issues using three very different tools: a simple model of stratospheric transport, which allows us to investigate the role of tropical transport in determining global transport timescales, satellite observations of long-lived tracers, which allow us to diagnose the seasonal variability of the tracer gradients that mark the transition between tropical and extratropical air, and a shallow water model, which allows us to investigate the mechanisms of tropical isolation in the simplest relevant dynamical framework. We first discuss the characteristics of analytical solutions for the mean age of air, a measure of the mean timescale for transport by large-scale processes in the stratosphere, in a simple, one-dimensional conceptual model of stratospheric transport. In this "leaky pipe" model, the stratosphere is divided into three regions: the tropics and the Northern and Southern extratropics. We examine the dependence of the mean age on advection, diffusive mixing, and quasi-horizontal transport between the tropics and the extratropics. This work provides insight into the role of the tropics in global chemical transport under the assumption of at least some degree of tropical isolation. We next examine the seasonal variability of the subtropical tracer gradients which mark the transition between tropical and extratropical air from both a diagnostic and a mechanistic standpoint. We use probability distribution functions of satellite measurements of long-lived tracers to define the transition regions, which are commonly called the subtropical "edges". We examine six and a half years of measurements and identify the central latitude, and in some cases the area, of these edges at eight pressure levels on quasi-monthly timescales. We compare the seasonal variability of the subtropical edges to the variability in several transport parameters and thus increase our understanding of the mechanisms of tropical isolation from a diagnostic standpoint. We then use a shallow water model, which represents many of the properties of the flow between two isentropic surfaces, to examine the mechanisms of the formation of the subtropical edges during each season. We include the effects of diabatic heating and cooling as well as planetary-scale wave propagation and examine the role of these processes in the formation of potential vorticity gradients that behave in much the same way as the observed subtropical tracer gradients. Our results indicate that the winter subtropical edge marks a mixing barrier. The rapid stirring in the winter hemisphere that results from planetary-scale wave breaking is generally confined to the midlatitudes, and the strong tracer and potential vorticity gradients in the winter subtropics likely result from "stripping" processes, as filaments of material are occasionally pulled out of the tropics by this mid-latitude stirring. The summer subtropical edge, however, does not mark a mixing barrier in the middle and upper stratosphere. Rather, it is likely that the strong subtropical tracer and potential vorticity gradients in the summer hemisphere result purely from the action of the residual circulation, which tends to increase potential vorticity and tracer values in the tropics and decrease them at high latitudes (for tracers with tropospheric sources and photochemical sinks) over the course of the summer. We show that the seasonal variability of the edges can, in some cases, contribute significantly to the mass budgets in simple "leaky pipe"-type models, but find that it is difficult to assess the role of this seasonal variability in tracer transport. / by Jessica L. Neu. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (leaves 211-214). / by Cynthia Dorothy Kidder Engholm. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (p. 281-287). / Anisotropy can exist in the subsurface as an intrinsic property, or as an induced property, or as a combination of both. Induced anisotropy can result due to preferred orientation of grains, thin layering, and/or the presence of fractures. In this thesis, we study the reflection moveout for Compressional and Shear waves in horizontally stratified azimuthally anisotropic media. Reflection moveout in common-midpoint (CMP) gathers is generally treated by an azimuthally-isotropic hyperbolic equation. Recently, special treatment for the reflection moveout in azimuthally anisotropic media has been introduced due to the fact that the moveout in such cases is azimuthally dependent. Here, the normal moveout (NMO) equation parameterized by the exact normal-moveout (NMO) velocity is studied. We verify numerically (through synthetic data) the accuracy of the exact (i.e., analytic) azimuthal description of the NMO velocity. We show that the azimuthal variation of the NMO velocity has, in general, a relatively simple elliptical form. We also show that the NMO equation is sufficiently accurate for P- and Shear-wave propagation on conventional spreadlengths (e.g., lenghts close to the reflector depth). The influence of anisotropy causes the deviation of the moveout curve from a hyperbola, even in a homogeneous anisotropic layer with a horizontal interface. Hence, reflection moveout in azimuthally anisotropic media is not only azimuthally dependent but it is also nonhyperbolic. / (cont.) To account for the nonhyperbolic moveout, we have derived an exact expression for the azimuthally dependent quartic coefficient of the Taylor series expansion for the two-way traveltimes [t2(x2)] that is valid for any pure mode of wave propagation. As a result, we introduce an analytic representation for the quartic coefficient for pure mode reflection in anisotropic medium with an arbitrary strength of anisotropy. In addition, we present an analytic expression for large-offset, nonhyperbolic reflection moveout (NHMO). Special attention is given in this study toward P-wave propagation in orthorhom-about the same for any strength of anisotropy. To invert for the NMO ellipse parameters at least three NMO-velocity measurements along distinct azimuth directions are needed. In order to maximize the accuracy and stability in parameter estimation, it is best to have the azimuths for the three source-to-receiver directions 60Ê» apart. Having more than three distinct source-to-receiver azimuths (e.g., full azimuthal coverage) enhances the quality of the estimates. The azimuthal variation of the NMO velocity in azimuthally anisotropic media can be utilized to invert for some of the medium parameters which can be useful in characterizing the zone of interest. In HTI media, for example, and using the P-wave reflection moveout, we can estimate three key parameters: the vertical velocity Vpvert, anisotropy parameter 6(V), and the azimuth a of the symmetry-axis ... / AbdulFattah Ahmed Al-Dajani. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990. / Includes bibliographical references (leaves 68-76). / by Duncan Southam Fisher. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (v. 2, leaves 273-291). / by Yan Song. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / 2 folded leaves in pocket. / Includes bibliographical references (leaves 261-272). / by Elizabeth Renee Schermer. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1987. / Microfiche copy available in Archives and Science. / Bibliography: leaves 83-86. / by Richard Peter Signell. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Page 177 blank. Cataloged from PDF version of thesis. / Includes bibliographical references (pages 171-176). / This doctoral thesis focuses on the application of geodetic techniques and finite element modeling to studying crustal deformation and other processes. In particular, it focuses on optimizing standard processing strategies, reducing the noise in the measurements and mitigating the effects of external processes in order to extract the signal of interest. Geodetic techniques, such GPS and InSAR, are still affected by major sources of errors, such as multipath, atmospheric effects, snow, blockage of the signal by infrastructure that can make difficult the detection of geophysical signal. In this thesis, I analyze three sets of data for which I have used different approaches to estimate the displacement and to investigate the sources of deformation that contribute to the signal. The first project consists of studying the deformation caused by the seasonal cycle of injection/withdrawal of gas in a depleted gas reservoir using InSAR measurements and Finite Element modeling techniques. In this project, I present a method to reduce the atmospheric signal, using statistical techniques and filtering and to estimate the error on the measurements. I compare the estimates with Finite Element modeling of the reservoir, using an elastic rheology. The second project analyses the unrest of Katla volcano in Iceland using GPS observables. GPS stations on top of the volcano register a complex signal, caused by the concurrence of different processes, such as snow on the antenna, multipath, earthquakes, volcanic deformation and hydrological events. In this project, I explore methods to detect the effects of snow/ice on top of antennas and to separate the different sources of the signal in order to extract the volcanic deformation component. I then compare the GPS measurements with a finite element model of snow/ice load on the volcano to validate the source of the estimated deformation. The third project involves the analysis of long term deformation and determination of vibrations of the Al-Hamra tower in Kuwait, using 24-hours averaged, 6-hours averaged and 1 Hz GPS measurements. The signals of GPS stations mounted on buildings are often affected by multipath due to reflective objects on the roof and suffer from reduced accuracy due to the partial masking of the sky by infrastructures on the roof. I explore different ways to mitigate the multipath, assessing an optimal GPS processing strategy for building installation. As the resulting deformation observed by the GPS instruments is highly correlated to variations in temperature, I present a finite element model of the building, where the major source of deformation is caused by a differential heating of the external walls. I also discuss the effects of the winds on the structure of the building, analyzing the high rate GPS measurements. / by Martina Coccia. / Ph. D.