Thesis: S.M. in Climate Physics and Chemistry, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 81-83). / This thesis works to evaluate the new rainfall algorithm that is used to simulate longterm tropical cyclone precipitation (TCP) climatology throughout the southeastern United States. The TCP climatology is based on a fleet of synthetic tropical cyclones developed using National Center for Atmospheric Research/National Centers for Environmental Prediction reanalysis data from 1980 to 2010 and the Coupled Hurricane Intensity Prediction System (CHIPS) model. The climatology is compared to hourly rainfall estimates from the WSR-88D Next Generation Weather Radar (NEXRAD-II) system. In general the synthetic TCP estimates show good agreement with radar-based observations. The rainfall algorithm appears to perform better at coastal locations versus inland ones, and in general has better agreement in the eastern locations considered in this study. In addition, the spatial dependence of radar rainfall estimates was addressed, and in general more extreme TCP-events exhibited a greater degree of event total precipitation variation at grid box-scale. Finally, preliminary work incorporating streamflow measurements as a metric for assessing TCP risk using the synthetic rainfall climatology was begun. Correlation between both grid box-specific and basin-average radar-based event TCP and surface streamflow measurements (from the U.S. Geological Survey National Water Information System) varied greatly, and was generally moderate, and future work should incorporate more thorough streamflow modeling in order to evaluate these comparisons. / by Sandra Michael Shedd. / S.M. in Climate Physics and Chemistry

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / by David Michael Sherman. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 169-177). / The recorded seismic signal contains full information about the source that generated the seismic waves and the path along which the seismic waves travel and interfere with subsurface. However, source information is not an explicit part of the seismic record and thus is a large source of uncertainty in seismic imaging and velocity analysis applications. In this thesis, we develop source-independent methods for seismic imaging, seismic trace interpolation and velocity analysis using the interference between pure (PP and SS) and converted-phase (PS and SP) waves. For seismic imaging, we develop amplitude-balancing source-independent converted-phase seismic imaging conditions and introduce a concept of conversion ratio coefficients to provide a physical and mathematical foundation for source-independent converted-phase (SICP) imaging. For seismic trace interpolation, we develop a scheme for migration/de-migration to suppress migration-based artifacts due to sparse station deployments. For velocity analysis, we present first a source-independent space-lag domain Extended SICP imaging condition (ESICP-IC). Then, we mathematically derive an optimization scheme for source independent converted-phase wave equation migration velocity analysis (SICP-WEMVA). We investigate numerically the stability and convergence of SICP-ICs, SICP interpolation and SICP-WEMVA with synthetic data. Finally, using the developed methodologies, we investigate the subsurface structure of the Hengill geothermal area in Iceland using the abundant micro-seismic activity of the region. The constructed SICP seismic images show detailed subsurface structure of the Hengill area that is well correlated with previous seismic and resistivity studies. Also, we find that the amplitudes of the images are well correlated with a low resistivity region of the geothermal area. The reason for this correlation is not fully understood, but may provide an additional tool for investigation of the Hengill site. / by Andrey Hanan Shabelansky. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 161-169). / The currently observed increase in atmospheric CO2 due anthropogenic emissions is substantially slowed by natural processes that incorporate CO2 into the terrestrial biota and the ocean. Year-to-year changes in the CO2 growth rate that exceed variations in the fossil fuel source indicate a significant variability in these global CO2 sinks. However, the enormous complexity of the terrestrial and oceanic biogeochemical systems that absorb atmospheric CO2 makes these sinks extremely difficult to understand and precisely quantify. Many techniques, including the interpretation of the relative changes in atmospheric CO2 and O2/N2, ocean modeling, and atmospheric data inversions, have been employed to estimate the mean and variability of global CO2 sinks. However, uncertainty remains large. The goal of this thesis is to improve understanding of global CO2 sinks by considering (1) the error in the atmospheric O2/N2 partitioning method due to the neglect of interannual variability in the air-sea fluxes of 02, and (2) the interannual variability of the ocean CO2 sink. / (cont.) A global, high-resolution ocean general circulation model is used to estimate the magnitude and understand the mechanisms of interannual variability in air-sea fluxes of both CO2 and 02. I find that the global variability in the fluxes of both gases are dominantly forced by large-scale physical processes governing upper ocean dynamics, particularly El Nifio / Southern Oscillation (ENSO) and, for 02, the North Atlantic Oscillation (NAO). Estimates of the extremes of CO2 and 02 flux variability for the period 1980-1998 are +/-0.5x1015 grams Carbon/yr (PgC/yr) and -70/+100x1012 mol/yr (Tmol/yr), respectively. Global 02 flux variability implies up to a 1.0 PgC/yr error in estimates of interannual variability in land and ocean CO2 sinks derived from atmospheric 02/N2 observations. This error is significant for estimates of annual sinks, but it is cumulatively negligible for estimates of mean sinks from October 1991 to April 1998. Increasing convergence of estimates of land. / by Galen Anile McKinley. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1984. / Vita. / Includes bibliographical references (pp. 366-377). / This dissertation represents a theoretical, numerical, and observational study of barotropic waves and turbulence in an inhomogeneous background flow environment. The theoretical aspects of the work are simplified by restricting attention to the two-dimensional doublyperiodic beta-plane, and in nearly every respect to large-scale zonal flows which are barotropically stable (in a normal-mode sense). The role of the flow inhomogeneity is investigated by considering both nonlinear and linear theory of wave, mean-flow interaction; the key concept to emerge is that of induced spectral transfer of conserved wave quantities by the basic-state flow. Along the way, some new nonlinear conservation laws are derived. In the special case examined of a large-scale zonal jet, the wave enstrophy is approximately conserved in a fully nonlinear sense, and the wave, mean-flow interaction may be characterized as an induced spectral transfer of the wave enstrophy along lines of constant zonal wavenumber k. Because of the scale separation, the linear part of the interaction problem can be closed by applying WKB ray-tracing theory. The turbulent dynamics act to smooth the spectral gradients by irreversible mixing of wave enstrophy; their closure is less easily quantified. The theoretical ideas are tested by performing numerical simulation experiments of both the spin-down and forced-dissipative equilibrium variety. In particular, the nature of the wave, mean-flow interaction can be identified by examining the interaction terms as functions of the meridional wavenumber X for fixed k. In so doing one can determine the point at which irreversible nonlinear dynamics take over from reversible linear dynamics; while the latter are characterized by induced transfer of enstrophy along lines of constant k, the former operate by diffusing energy and enstrophy across such contours. Finally the ideas of the thesis are applied to atmospheric data, and the results used to interpret the observed nonlinear spectral fluxes of kinetic energy and of enstrophy, as well as the interaction between the stationary (viz. one-month time-mean) and transient flow components. / by Theodore Gordon Shepherd. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Microbial sulfate reduction (MSR) utilizes sulfate as an electron acceptor and produces sulfide that is depleted in heavy isotopes of sulfur relative to starting sulfate. The fractionation of S-isotopes is commonly used to trace the biogeochemical cycling of sulfur in nature, but a mechanistic understanding of factors that control the range of isotope fractionation is still lacking. This thesis investigates links between the physiology of sulfate reducing bacteria in pure cultures and multiple sulfur isotope (³², ³³, ³⁴34S, and ³⁶S) fractionation during MSR in batch and continuous culture experiments. Experiments address the influence of nutrient and electron donor conditions, including organic carbon, nitrogen, and iron, in cultures of a newly isolated marine sulfate reducing bacterium (DMSS-1). An actively growing culture of DMSS-1 produced sulfide depleted in ³⁴S by 6 to 66%o, depending on the availability and chemistry of organic electron donors. The magnitude of isotope effect correlated well with the cell specific sulfate reduction rate (csSRR), and the largest isotope effects occurred when cultures grew slowly on glucose, a recalcitrant organic substrate. These findings bridge the long-standing discrepancy between the upper limit for S-isotope effect in laboratory cultures and the corresponding observations in nature and indicate that the large (>46 %o) fractionation of S-isotopes does not unambiguously record the oxidative sulfurrecycling. When the availability of iron was limited, the increase in S-isotope fractionation was accompanied by a decrease in the cytochrome c content as well as csSRR. In contrast, growth in nitrogenlimited cultures increased both csSRR and S-isotope fractionation. The influence of individual enzymes and electron carriers involved in sulfate respiration on the fractionation of S-isotopes was also investigated in cultures of mutant strains of Desulfovibrio vulgaris Hildenborough. The mutant lacking Type I tetraheme cytochrome c₃ fractionated ³⁴S/³²S ratio 50% greater relative to the wild type. The increasing S-isotope fractionation accompanied the evolution of H2 in the headspace and the decreasing csSRR. These results further demonstrate that the flow of electrons to terminal reductases imparts the primary control on the magnitude of the fractionation of S-isotopes, suggested by culture experiments using DMSS-1. / by Min Sub Sim. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-135). / This dissertation contributes to three unresolved problems in planetary science regarding potential dynamo action in asteroids, the Moon, and Mars. First, we examine the physical processes active during asteroid core crystallization. We model inward crystallization as well as crystal settling and the compaction of a possible cumulate inner core. We then explore the potential strength and longevity of a dynamo in the planetesimal's early history. We find that cumulate inner core solidification would be capable of sustaining a dynamo during the bulk of solidification, but that there may be insufficient power for a dynamo in an inward dendritic solidification scenario. Next, we explore the origin of the magnetic field recorded in the lunar crust. Evidence suggests a core dynamo existed from 4.2 to 3.56 Ga, and possibly until near present day. Seismic measurements indicate the lunar core is partially solidified. Latent heat and concentrated light elements at the interface of a solidifying inner core could drive outer core convection. We demonstrate that core solidification can account for the observationally inferred duration of the lunar dynamo. However, it cannot explain the magnitude of the recorded magnetic field. A dynamo may also stop and restart due to heat flow fluctuations as convective vigor falls below the threshold for dynamo action. Finally, we examine the early history of the Martian mantle. The solidification of a magma ocean may result in an unstable density profile prone to overturn. A long-wavelength instability could play a role in the stark contrasts observed between the northern and southern hemispheres of Mars, including the dichotomy in crustal thickness and magnetization. However, we find that cumulate overturn in the Martian scenario would likely have occurred with short wavelengths. In an isoviscous model, thermal convection ensues rapidly after overturn; however, when viscosity is temperature dependent, compositional stability suppresses the onset of convection. / by Aaron Lewis Scheinberg. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references. / This thesis examines the response of alpine landscapes to the onset of glaciation. The basic approach is to compare fluvial and glacial landscapes, since it is the change from the former to the latter that accompanies climatic cooling. This allows a detailed evaluation of hypotheses relating climate change to tectonic processes in glaciated mountain belts. Fieldwork was carried out in the eastern Sierra Nevada, California, and the Sangre de Cristo Range, Colorado, alongside digital elevation model analyses in the western US, the Southern Alps of New Zealand, and the Himalaya of northwestern Pakistan. The evidence presented here suggests that the so-called "chicken-and-egg" hypothesis is overstated in its appeal to glacial erosion as a major source of relief production and subsequent peak uplift. Glaciers in the eastern Sierra Nevada and the western Sangre de Cristos have redistributed relief, but have produced only modest relief by enlarging drainage basins at the expense of low-relieftopography. Glaciers have lowered valley floors and ridgelines by similar amounts, limiting the amount of "missing mass" that can be generated, and causing a decrease in drainage basin relief. / (cont.) The principal response of glaciated landscapes to rapid rock uplift is the development of towering cirque headwalls. This represents considerable relief production, but is not caused by glacial erosion alone. Large valley glaciers can maintain their low gradient regardless of uplift rate, which supports the "glacial buzzsaw" hypothesis. However, the inability of glaciers to erode steep hillslopes as rapidly can cause mean elevations to rise. Cosmogenic isotope dating is used to show that (i) where plucking is active, the last major glaciation removed sufficient material to reset the cosmogenic clock; and (ii) former glacial valley floors now stranded near the crest of the Sierra Nevada are at varying stages of abandonment, suggesting a cycle of drainage reorganisation and relief inversion due to glacial erosion similar to that observed in river networks. Glaciated landscapes are quite distinct from their fluvial counterparts in both landforms and processes. Given the scarcity of purely fluvial, active mountain ranges, it is essential that glacial erosion be considered amongst the processes sculpting active orogenic belts. / by Simon H. Brocklehurst. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 63-64. / by Peter Paul Neilley. / M.S.

Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 69-75). / Tropical cyclones (TCs) are among the most expensive and lethal geophysical hazards. Studies suggest that the intensity of TCs will increase due to the thermodynamic effects of anthropogenic greenhouse gas input. In contrast, while aerosols are shown to have an overall cooling effect on global climate, their impact on TCs is not yet well-understood. This paper explores the influence of the sulfate aerosol first indirect effect (AIE) on Atlantic hurricane intensity and genesis. I use a single-column radiative convective model that incorporates the first AIE (aerosol enhancement of cloud reflectivity) through parameterization of cloud droplet number, radius, and optical depth. Cloud droplet number is parameterized using an empirical scheme, while the radius is determined from cloud liquid water content and number concentration moments, and the optical depth scheme is embedded in the original single-column model. The model is run with both the IGAC/SPARC Chemistry Climate Model Initiative (CCMI) historical simulations of sulfate concentrations over the hurricane main development region during hurricane peak season (August-October) and a self-generated inventory of sulfate concentrations based on realistic vertical variability in sulfate levels. The model was run to radiative-convective equilibrium (RCE), then rerun under weak temperature gradient mode (WTG). Runs successfully produce the Twomey or first indirect effect, which states that increased aerosols will increase cloud droplet number concentration, decrease the effective cloud droplet radius, and increase the cloud optical depth. The net effect is increased reflection of radiation from the atmosphere, which theoretically cools the Earth, decreasing the potential intensity and genesis potential of TCs. While model runs produce the expected changes in cloud properties, cloud cover is not sufficient for sulfate concentrations to have a substantial impact on hurricane activity via the AIE when the model is run to RCE. The WTG mode is then implemented with the goal of producing low-lying stratocumulus clouds to increase total cloud cover, but the single-column WTG scheme was not able to produce stratocumulus that did not also produce an overly strong negative feedback. Using the single-column model, one can demonstrate the indirect effect of sulfate aerosols on cloud reflectivity and that sufficient cloud cover is needed to produce a noticeable cooling and change in expected hurricane behavior. A further study of the subject could include parameterization of the poorly-understood cold or mixed-phase clouds, which can include characterization of additional aerosol types. In addition, a two-dimensional model has greater capacity to model phenomena such as low-lying stratocumulus, which could produce a more substantial ambient effect. / by Hao-yu Derek Chang. / S.M.