Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005. / Includes bibliographical references. / The central Nepalese Himalaya are characterized by a sharp transition in physiography that does not correlate with previously mapped faults. Rates of rock uplift, erosion, and exhumation for rocks surrounding this physiographic transition are investigated using digital topographic data, ⁴⁰Ar/³⁹Ar thermochronology, cosmogenic radionuclides, and thermal modeling, to determine whether this break in landscape morphology reflects active tectonic displacements at the foot of the Himalaya. The goals of the thesis are 1) to understand the degree to which landscape morphology can be used to delineate breaks in rock uplift in active orogens; 2) to characterize the neotectonics of central Nepal using data representing varied temporal and spatial scales of inquiry; and 3) to move closer to understanding the dynamic interactions among climate, erosion and tectonics in a field setting. Analysis of digital topographic data from Nepal and other tectonically active settings demonstrates how breaks in the simple scaling characterizing river systems can be used to identify tectonic boundaries. / (cont.) Limitations to these methods are illustrated by way of an example from the Eastern Central Range of Taiwan, but changes in landscape morphology become the foundation upon which further investigations are built for central Nepal. These investigations include data from detrital ⁴⁰Ar/³⁹Ar thermochronology to characterize changes in exhumation rates at million-year timescales; cosmogenic ¹⁰Be to characterize changes in erosion rates at millennial timescales; and simple thermal modeling to evaluate a range of alternative tectonic geometries for central Nepal. The data point to the existence of a tectonically significant, thrust- sense shear zone at the base of the high Himalaya in central Nepal, nearly 100 km north of the active thrust front. The existence of this fault zone in a location where the Indian summer monsoon is concentrated is consistent with the predictions of numerical and analytical models of orogenic growth, which suggest a direct feedback between focused erosion and tectonic displacements in active orogens. / (cont.) Future work is warranted to evaluate the persistence of climatic and tectonic signals over a variety of time and space scales in central Nepal, and to determine whether correlations between climate and tectonics exist in other field settings. / by Cameron W. Wobus. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (p. 135-143). / by Einat Aharonov. / Ph.D.

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 53-57). / Difficulties encountered in reproducing Mercury's compositional attributes through modeling of formational processes have bolstered support for the hypothesis that one or more giant impacts stripped away a significant proportion of proto-Mercury's silicate mantle. Previous investigations demonstrate sufficient removal of mantle material to account for the planets unusually high mean density, but do not consider the effects of multiple silicate and oxide phases. In this study, we extend the present theory by investigating the consequences of a more realistic chemical model on the evolution of the ejected material. We suggest that the majority of condensation within the expanding vapor plume can be modeled as an equilibrium process following homogeneous nucleation of refractory phases leading to larger particle sizes than previously estimated. We use a thermodynamic model focused on major element composition of ejected material to analyze the effect of differential condensation on the expansion and final state of ejecta. We also adapt pre-existing models for chemistry of condensation and impact shock compression to address additional problems associated with the process. For ejecta of sufficiently high specific entropy, our simplified chemical models indicate that energy released during condensation of MgO-rich phases buffers the temperature, delaying or preventing onset of FeO condensation. If sufficient spatial separation between condensates and vapor arises or if significant amounts of uncondensed FeO vapor remain uncondensed, reaccumulated ejecta would be enriched in MgO and refractory phases. This is compatible with an FeO depletion of Mercury's surface relative to other terrestrial bodies as some spectroscopic data suggests. The proposed process leads to a greater depletion in FeO and a lesser depletion in refractory, incompatible elements (Al2 O3, CaO, TiO2 ), than models assuming uniform removal of material from a differentiated proto-Mercury. / by Sean M. Wahl. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (leaves 49-50). / A state estimate produced by ECCO-GODAE from a global one-degree model and data spanning the years 1992-2005 is analyzed in terms of transports of volume, temperature, and freshwater. The estimate is assessed to be sufficiently close to observations to merit analysis. The methods of analysis are similar to those of Stammer et al. (2003). The longer time period allows trends to be measured with greater confidence. Time mean flow characteristics demonstrate agreement with previous estimates. The strength of the ACC (146±5Sv) is larger than in the Stammer et al. (2003) state estimate, but is within the range of other estimates. A twelve-year decreasing trend is observed in the strength of the ACC of approximately 0.88Sv/year. The Indonesian throughflow transport of 1 l±2Sv is within the expected range. There is also a decreasing twelve year trend in the strength of the ITF of 0.065Sv/year. The ITF is stronger in boreal summer than boreal winter by approximately 4Sv. A strong annual cycle is present in the transport record on most sections, but higher frequency variability is also present. Most temperature transport variability results from velocity fluctuations, except in the Southern Ocean where temperature fluctuations are more important. Recommended further work includes a more detailed analysis of variability in this state estimate. / by Elise Olson. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010. / 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. 185-195). / Midlevel ventilation, or the flux of low-entropy air into the inner core of a tropical cyclone (TC), is a hypothesized mechanism by which environmental vertical wind shear can constrain a TC's intensity. An idealized framework is developed to assess how ventilation affects TC intensity via two pathways: downdrafts outside the eyewall and eddy fluxes directly into the eyewall. Three key aspects are found: ventilation has a detrimental effect on TC intensity by decreasing the maximum steady state intensity, imposing a minimum intensity below which a TC will unconditionally decay, and providing an upper ventilation bound beyond which no steady TC can exist. Based on the idealized framework, a ventilation index is derived that is equal to the environmental vertical wind shear times the midlevel entropy deficit divided by the potential intensity. The ventilation index has a strong influence on the present-day climatology of tropical cyclogenesis and the distribution of TC intensification. Additionally, changes in the ventilation index are also examined in general circulation models (GCMs) between the late 20th century and the late 22nd century. Individual GCMs indicate potential regional shifts in preferred locations of tropical cyclogenesis and changes in TC intensity statistics due to shifts in the seasonal ventilation index, but a statistically significant projection cannot be given. The GCMs do show a robust increase in the midlevel entropy deficit and potential intensity nearly everywhere in the tropics. Lastly, an axisymmetric model with parameterized ventilation is used to examine the sensitivity of TC intensity to the strength and location of the ventilation and to examine the findings of the idealized framework. Increasing the strength of the ventilation and placing the ventilation at lower to middle levels results in a greater decrease in the quasi-steady intensity, whereas upper-level ventilation has little effect on the intensity. For strong ventilation, an oscillatory intensity regime materializes and is tied to transient convective bursts and strong downdrafts into the boundary layer. The sensitivity of TC intensity to ventilation can be viewed in the context of a modified thermal wind relation or the fractional Carnot efficiency of the inner-core. / by Brian Hong-An Tang. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 45-47). / Nitrous oxide (N2O) is a powerful greenhouse gas and ozone depleting substance, but its natural sources remain poorly constrained. Marine emissions are likely much higher than IPCC estimates predict, due to unusually high emissions from the oxygen minimum zones (OMZs) in the eastern tropical Pacific and Arabian Sea that are not accounted for in assessments. Measurements of atmospheric concentrations from a selection of AGAGE stations around the Pacific Ocean were combined with back-trajectories calculated using the HYSPLIT4 atmospheric model, in order to study the relative importance of OMZs on Pacific N2O emissions. Spatial and temporal variability in nitrous oxide concentrations were analyzed in order to determine potential regions of higher emissions, as well as the impacts of ENSO on biogeochemistry in the OMZs. Air parcels that passed over the oxygen minimum zone in the Eastern Tropical South Pacific were found to have N2O concentrations as much as 0.5 ppb higher than average. Average concentrations over the OMZ were modulated by an additional ~0.2 ppb higher during La Niia events and ~0.2 ppb lower during El Niio periods, a deviation of the same order of magnitude as N2O's seasonal cycle. Comparisons with CFC-12 and SF6 suggested strong influences on nitrous oxide concentrations in the Southern Hemisphere from stratosphere-troposphere exchange, but little influence from inter-hemispheric transport. / by Elisabeth L. Boles. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (p. 74-80). / by Mousumi Roy. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (leaves 302-311). / by David Anton Dinter. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995. / Includes bibliographical references (leaf 15). / by Janice A. Vatland. / B.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 78-79. / by Robert Paul d'Entremont. / M.S.