Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmosphere and Planetary Sciences, 1987. / Bibliography: p. 179-182. / by James S. Risbey. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986. / Microfiche copy available in Archives and Science / Includes bibliographies. / by Yves Bernabe. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 1999. / "September 1998." / Includes bibliographical references (leaves 127-130). / The Asian summer Monsoon circulation is driven by differential thermal heating, primarily associated with the localized latent heat release from enhanced precipitation over the India sub-continent. Although this heating is of limited zonal extent, it drives a time-averaged, upper level anticylone which is of global extent, extending from the western edge of the bulge of Africa, to the east of the Asian continent. The current theory (originally proposed by Gill (1980)) for explaining this zonally asymmetric component of the tropical circulation is unsatisfactory because it is based on the linear theory of damped equatorial waves while it is known that, at least for the upper level flow near the tropopause, the dynamics are strongly nonlinear. An alternative explanation, which is consistent with the nonlinear nature of the flows, involves the shedding of vortices from the directly forced monsoon anticyclone. The vortices, or eddies, are capable of drifting to the far field to establish a circulation which extends far beyond the local forcing. This thesis provides a dynamical explanation for the generation of eddies near the center of a divergent anticyclone, which, through their westward drift are responsible for the establishment of the global scale of the Asian summer Monsoon. The thesis consists of two parts, one numerical and one observational. The numerical study systematically investigates localized thermally driven circulations by using a shallow water model. This part of the thesis is theoretical in nature, and seeks to understand how non-axisymmetric elements such as a beta effect, or an external uniform flow, affects the dynamics of a divergent anticyclone for which, in the absence of non-axisymmetric elements, there exists an analytical axisymmetric solution. Control parameters which determine the dynamical regime of the flow are identified and explained. For the midlatitude beta plane experiment, the control parameter, pO, is the ratio between the free drift speed of an axisymmetric vortex on a beta plane, OL, and the strength of the forced localized divergent flow (ux) where L is the size of the axisymmetric circulation. For the uniform flow experiments, the control parameter is the strength of the uniform flow, Urn, and the divergent flow, ux. Each control parameter measures the relative importance of two competing effects, one which tries to displace the anticyclone westward (for the midlatitude beta plane experiments), or downstream (for the uniform flow experiments) and one tries to keep the forced vortex anchored. For each series of experiments, a critical value which separates the different long-time flow behavior is found. When the circulation is below the critical value, the circulation is persistent and localized. When the control parameter is above the critical parameter, a material filament with low potential vorticity is drawn from the divergent center, rolls up due to shear instability and is soon shed away by detaching itself from the main vortex. In the time-mean vorticity budget, the transient eddies have the effect of dissipating the time-mean flow. The dissipation effect by transient eddies can be grossly parameterized as a linear damping term in the linear version of the model. Another series of experiments, extending the midlatitude beta plane to the equatorial beta plane, with an equator within the reach of the forced perturbation, is conducted in which equatorial waves can be generated. The shedding behavior begins when the value of the control parameter is of order unity in the midlatitude beta plane experiments, and continues to exist for values of order 10 in the equatorial beta plane experiments. When the control parameter takes on values of order 100 and larger, the shedding behavior disappears and is replaced by linear wave solutions. In these experiments, another non-dimensional parameter (q), which measures the non-dimensional distance from the thermal forcing center to the equator, is found to affect the stability characteristics of the forced vortex. This series of experiments also allows equatorial waves to co-exist with the nonlinear vortex and to be excited by the broad thermal cooling, whose magnitude and location are determined by the internal dynamics of the nonlinear forced vortex. This linear part of the response is similar to the solution predicted by Gill (1980), but is of opposite sign, since it is the response to the resulting broad thermal cooling part of the thermal forcing, and not the small localized imposed thermal heating as Gill would have it. In the second part of the thesis, the theory is confirmed by discovering eddy shedding from the analysis of observational data. The potential vorticity on the isentropic surfaces are analyzed from 17 isobaric level NCEP-reanalysis data over the region of the Asian summer Monsoon. Two episodes of eddy shedding are found in July of 1990. The shedding events in the potential vorticity field are observed at the levels of isentropic surfaces from 360K to 380K. The induced geopotential perturbation penetrates deeper to 400 mb. The technique of Contour Advection with Surgery, a technique that allows to discriminate between adiabatic and diabatic effects, is used to recapture the shedding events, and confirm that the eddy shedding is indeed due to the essentially inviscid process identified in the idealized shallow water model. / by Chia-hui Juno Hsu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (p. 274-287). / by Carlos F. del Pozo. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2005. / Cataloged from PDF version of thesis. Pages 29-37, 42 and 46 not in original thesis. / Includes bibliographical references (pages 44-48). / We explored two complementary mechanisms for change in porosity and permeability of geomaterials: thermal cracking and crack healing by diagenesis. A suite of thermal cracking experiments was performed on andesite plugs from the geothermal field in Awibengkok, Indonesia. Permeability (k) and specific storage capacity were measured by the oscillating flow method in a wide range permeameter, at room temperature, with effective pressures between 15 MPa and 95 MPa, before and after thermal cracking. The samples were cracked at 150 and 300 °C and ambient pressure. Andesite samples have low permeability, on the order of 10-²⁰ M² . With increased pressure, permeability is reduced by a factor of two. Contrary to expectations, thermal cracking reduced the permeability of this material by an order of magnitude. We also examined a set of samples from crack healing experiments performed on Sioux quartzite by M. Messar. In these experiments the quartzite permeability fell by three orders of magnitude within a few days when the samples were saturated with water and heated to temperatures from 300 to 500 °C and pressures from 25 to 200 MPa. In order to correlate Messar's permeability measurements and experimental conditions with visual observations of the pore structure (mainly consisting of grain boundary cracks), we took scanning electron microscope micrographs of the samples. We then counted the intersections of test lines with healed and unhealed cracks. This yielded a set of measurements of the crack area per volume of the quartzite. We found that the final permeability of the samples was related to the area per volume of unhealed cracks by a power relation. Combining the findings from the two sets of experiments, it seems that cracking and healing effects due to the ambient temperature and pressure in geothermal fields such as Awibengkok could eliminate any permeability through grain boundary scale cracks within a matter of days. / by Susannah Dorfman. / S.B.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 211-215. / by Bradley Roy Colman. / Sc.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 44-50). / Stromatolites, columnar rock-like structures, are potentially some of the oldest, microbially mediated fossils visible in the rock record; if biogenesis is able to be confirmed for these ancient stromatolites, some being greater than 3 billion years old, these ancient stromatolites could be used to demonstrate the microbial community assemblages throughout ancient time. Hamelin Pool, Shark Bay, Australia is an ideal field site for this task, as stromtolites and modern microbial mats coexist and the microbial mats have been shown to contribute to the formation of the stromatolites. Comprehensive lipid biomarker profiles were determined in this study for non-lithified smooth, pustular, and colloform microbial mats, as well as for smooth and colloform stromatolites. Intact polar lipids, glycerol dialkyl glycerol tetraethers, and bacteriohopanepolyols were analyzed via liquid chromatography-mass spectrometry (LC-MS) coupled to a Quadropole Time-of-Flight (QTOF) mass spectrometer, while the previously studied fatty acids (Allen et al., 2010) were analyzed using gas chromatography-mass spectrometry (GC-MS) to prove consistent signatures. From the lipid profiles, sulfate-reducing bacteria and anoxygenic phototrophic bacteria and archaea could be inferred. The presence of the rare 3-methylhopanoids was discovered in a significant portion of the samples, which could add to the characterization of this molecule, which has only been concretely linked to oxygenic conditions for formation. In accordance with Allen et al. in 2010, 2-methyhopanoids were detected, as well as limited signals from higher (vascular) plants. While the lipid profiles for all sediment types were similar, there were some differences that are likely attributable to morphological differences. However, the overall similarities suggest microbial communities can be similar between non-lithified microbial mats and stromatolites. / by Elise McKenna Myers. / S.B.

Thesis: Ph. D. in Planetary Sciences, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Orbital spacecraft make observations of a planet's surface in the present day, but careful analyses of these data can yield information about deeper planetary structure and history. In this thesis, I use data sets from four orbital robotic spacecraft missions to answer longstanding questions about the crustal structure of the Moon and the climatic history of Mars. In chapter 2, I use gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to constrain the quantity and location of hidden volcanic deposits on the Moon. In chapter 3, I combine GRAIL data with elevation measurements from the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) to investigate the nature of isostatic compensation in the lunar highlands. In chapter 4, I present a new technique for analysis of the Martian polar layered deposits (PLDs). In chapter 5, I apply that technique using images of the PLDs from the MOC and HiRISE instruments aboard the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) to constrain their ages and deposition rates. / by Michael M. Sori. / Ph. D. in Planetary Sciences

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (p. 34-37). / We apply a generalized Radon transform (GRT) to the study of the transition zone discontinuities. The transition zone discontinuities, e.g. the '410' and '660', result from mineral phase changes that occur at depths constrained by temperature and chemistry, and can provide information about the conditions of the mantle within the transition zone. Previous global studies of topography on the transition zone discontinuities use SS data and are limited by the low lateral resolution provided by SS waves, on the order of about 1000 kilometers. The GRT employs inverse scattering theory to image perturbations in mass density and elastic parameters of a medium, and can resolve structure on the order of 100 kilometers; the limit of this resolution has yet to be tested. This study maps discontinuity depths in the northwest Pacific Ocean with a lateral spatial sampling of 1° and a vertical sampling of five kilometers. We observe striking variations in the depth, strength, and continuity of the '410', '520', and '660' seismic discontinuities, as well as the presence of structure beyond the bounds of what is traditionally considered to be the transition zone. Topographies on the '410' and '660' are alternately positively and negatively correlated, suggesting that both composition and temperature contribute to the observed depths. Preliminary analysis of '410' depths, which assumes no variations in chemistry, yields an upper bound for temperature variations of ±280K. Future tests and data preprocessing should further improve the GRT results. / by Rosalee Alicia Lamm. / S.M.

Thesis: Ph. D. in Climate Physics and Chemistry, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / 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 97-111). / I present work on the relationship between inorganic atmospheric aerosol impacts and their precursor emissions from the United States of America. The inorganic aerosol ions nitrate (NO--₃), sulfate (SO²-- 4 ), and ammonium (NH+4 ) form from emissions of nitrogen oxides (NOx), sulfur dioxide (SO₂), and ammonia (NH₃). Emissions of NOx and SO₂ in the US have recently decreased, by 42% and 62% respectively for annual totals between 2005 and 2012, in response to economic, political, and technological developments. Under such large changes, the processes of aerosol formation may behave nonlinearly. The sensitivity of aerosol impacts to future emissions reductions -- the change in a metric per unit change in emissions -- can be very different from the sensitivity to past reductions. In this thesis, I use a chemical transport model to examine the sensitivities, changes in sensitivities, and the importance of nonlinear interactions for both health and climate impacts of inorganic aerosols. The first section of this thesis focuses on surface concentrations of inorganic fine particulate matter (PM₂.₅), a relevant metric for human health. In winter, PM₂.₅ across the central US is primarily composed of ammonium nitrate, whose formation is highly dependent on thermodynamics. The recent NOx and associated total nitrate (HNO₃+NO--₃ ) reductions have made aerosol formation in this region limited by total nitrate availability. Future NOx emissions reductions will thus have a much larger impact than they would have in the past. In summer, SO²-- ₄ aerosols dominate PM₂.₅. The reduced NOx emissions lead to higher peroxide concentrations and faster aqueous SO₂ oxidation, without increasing sulfate wet deposition to the same degree. With faster oxidation, a larger fraction of the emitted SO₂ forms sulfate and particulate matter, increasing the sensitivity of surface aerosol concentrations to SO2 emissions even as emissions themselves have decreased. These results suggest that NOx and SO₂ emissions reductions will continue to improve US air quality. The second section of this thesis focuses on sensitivities of the direct radiative effect (DRE) of inorganic aerosols to US emissions, a key quantity for studying climate impacts. The DRE and changes in DRE in winter are largest over the ocean. The summertime DRE includes a long tongue of advected aerosols over the Atlantic as well as a broad area of large DRE over the eastern US. As with surface concentrations, sensitivity of DRE to NOx and SO₂ emissions increased between 2005 and 2012, while sensitivity to NH3 emissions decreased. A simple scaling estimate of the DRE in the 2012 case from the 2005 DRE and sensitivities overestimates the magnitude of the DRE by 10.3mWm-² in January and 21.4mWm-2 in July. These values are equivalent to underestimating the SO₂ emissions reductions by 13.6% and 10.6%, respectively. These processes cause small errors for climate studies that assume scaling of aerosol radiative effects for current conditions, but greater errors could occur under future emission changes. / by Jareth Ian Holt. / Ph. D. in Climate Physics and Chemistry