Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 34). / Binary asteroids have been insightful to scientists in recent years in their quest to better understand the Solar System in its early stage. Observing a mutual event between a primary and its moon can yield the sizes of the objects in units of the semi-major axis a. When the linear dimensions of the orbit can be known, Kepler's Third Law allows for a solution of the mass. As an example, because the absolute linear scale of (22) Kalliope/Linus is known [1], one can determine the component sizes and reduce error bars on the mass and density of this M-type asteroid. Since the bulk composition is known from spectral data, the porosity of the asteroid can be calculated. Knowing the porosity of the asteroid can give scientists a better understanding of its formation and dynamical evolution. Binary object (22) Kalliope/Linus is a classic example of a system for which this technique can yield valuable results. An observing campaign involving five observers resulted in twenty-eight nights of data. The data were used to create rotational lightcurves, which were scanned for signatures of mutual events. / by Emily A. Kramer. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993. / Includes bibliographical references (p. 317-318) / by Catherine L. Summa. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (leaves 95-102). / by John Forest Olson. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Includes bibliographical references (leaves 213-216). / by Xiaoming Wang. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 23). / This project studies the sensitivity of model output statistics (or MOS) in numerical weather prediction to lead times and parameters. In order to study MOS in an idealized setting, I use the simplified Lorenz system of differential equations as the physical model to explore the sensitivity of linear MOS in this non-linear system. MOS finds a statistical relationship between imperfect model variables and true variables using linear regression. The effect on the forecast error of lead time and parameter perturbation are investigated. / by Joshua S. Coblenz. / S.M.

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 251-283). / The first magnetic fields in the solar system were embedded in the ionized gas of the protoplanetary disk itself. Soon after, newly formed protoplanets may have harbored magnetic core dynamos. Paleomagnetic analysis of ancient samples permits direct constraints on these early solar system magnetic fields. Here I present paleomagnetic studies of several classes of meteorites. Experiments on inclusions of chondritic meteorites have led to some of the first constraints on the intensities of protoplanetary disk magnetic fields. Meanwhile, measurements of eucrites, a class of achondrites believed to originate from the asteroid Vesta, suggest that Vesta once hosted a magnetic core dynamo. New techniques developed during the course of these measurements permit ongoing and future investigations of the remanent magnetizations of new meteorites and terrestrial rocks. In support of the paleomagnetic results, I present analytical and numerical modeling of magnetic dust grain dynamics in the solar nebula and of the interior dynamics of differentiated asteroids capable of hosting magnetic dynamos. / by Roger R. Fu. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 173-193). / This thesis posits that understanding the controls on microbially-mediated marine biogeochemical cycling requires a mechanistic description of microbial activity in biogeochemical models. In the work here, the diverse microbial community is resolved using metabolic functional types, which represent metabolisms as a function of their underlying redox chemistry and physiology. In Chapter 2, I use a simple model to predict the limiting oxygen concentration of aerobic microbial growth in an ecosystem. This limiting concentration is in the nanomolar range for much of the parameter space that describes microbial activity in marine environments, and so anticipates the recent measurements of oxygen to nanomolar concentrations or lower in anoxic zones. Anaerobic metabolisms should become favorable at this limiting concentration. The model provides a parameterization for dynamic oxygen depletion and limitation, without a prescribed critical oxygen concentration. In Chapter 3, I extend the above analysis to determine the full set of conditions required for favorable anaerobic metabolism. Resource ratio theory is used to explain the competitive exclusion of anaerobic metabolisms in oxygenated environments as well as the stable coexistence of aerobic and anaerobic metabolisms when oxygen is limiting. The onset of this coexistence is a function of the relative availability of oxygen and a mutually required substrate. Results hypothesize the likelihood of coexisting aerobic and anaerobic metabolisms at limiting oxygen concentrations, which is consistent with observations. These dynamics are demonstrated in an idealized oxygen minimum zone model. In Chapter 4, I use a mechanistic description of nitrification to explain the location and intensity of the primary nitrite maximum. First, competition with phytoplankton excludes nitrification from the sunlit layer of the ocean, resulting in peak nitrification at depth, as widely observed. Second, differences in the metabolisms of the microbial clades responsible for the two steps of nitrification explain why nitrite accumulates consistently as an intermediate. The model provides a dynamic resolution of nitrification in the ocean. It predicts that nitrification is favorable in sunlit waters where phytoplankton growth is limited by light or by a substrate other than reduced inorganic nitrogen. / by Emily Juliette Zakem. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. / Includes bibliographical references (leaf 33). / A record of carbon dioxide for the last 400,000 years revealed that atmospheric CO2 decreased from a pre-industrial concentration of 280 ppmV to approximately 200 ppmV during the last glacial maximum (Petit et al., 1999). Several hypotheses as to why this happened have been suggested yet no one explanation has been able to fully account for this decrease. Deep water is the main sink for carbon in the ocean through the biological pump, where the organic matter and CaCO3 shells of dead surface biota sink. The stored carbon in the deep ocean is 'aired' in the southern polar ocean, where large amounts of deep water are upwelled to the surface. Stephens and Keeling (2000) have proposed that if the southern polar ocean was covered with ice during the last glacial maximum, this would have prevented carbon stored in the deep ocean to be released into the atmosphere, thereby reducing the concentration of atmospheric CO2. Stephens and Keeling (2000) created a six-box ocean to test this hypothesis and were able to produce a 67 ppmV decrease of atmospheric CO2 from the pre-industrial concentration when only the gas exchange between the southern polar ocean and the atmosphere was limited. Based on the Toggweiler and Sarmiento (1985) three-box ocean model, a four-box ocean model that splits the Toggiweiler and Sarmiento polar ocean box in to a northern and southern component was created. The four-box ocean model examined the sensitivity of atmospheric CO2 to limitations in the airsea gas exchange for the southern polar ocean. The four-box ocean was able to produce seventy percent of Stephens and Keeling's decrease in atmospheric CO2 when the air-sea gas exchange was limited in the southern polar ocean. In addition, the four-box ocean model calculated carbon-14 concentrations in the ocean, which provide a useful constraint on model results that was not presented in the Stephens and Keeling model. The atmospheric carbon dioxide in the four box model was found to be more sensitive to increasing biological productivity in the southern polar ocean than to the growth of the Antarctic ice sheet. / by Stacey A. Archfield. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. / Includes bibliographical references (leaves 82-84). / Many modeling studies of tropical cyclones use the bulk aerodynamic formulae to determine angular momentum and enthalpy fluxes at the sea surface. These results show that the intensification of a hurricane is very sensitive to the values of the coefficients defined in these formulae (Emanuel, 1995). Using these formulae allows the model to make bulk estimates of these fluxes as a function of wind speed, without having to consider the full complexity of the physics of the air-sea interface. Generally, a complete treatment of fluxes would require modeling a number of small-scale physical processes, e.g. wave field response to the duration and fetch of the wind, sea spray processes, and convective stability of the boundary layer. The coefficients to these equations, Cd and Ck, have been empirically determined in previous studies, either by direct measurements on platforms and ships (Large and Pond, 1981), or by budget analyses from airborne data. However, these studies do not provide results for the high winds speeds encountered in strong hurricanes. Previous work has suggested that the coefficients do not remain constant, but rather are a function of wind speed. Producing values for these coefficients at high wind speeds will improve the accuracy of the numerical models. Recent advances in dropsonde technology (Hock and Franklin, 1999) provide improved range and accuracy from earlier methods, with reliable measurements of wind and thermodynamic variables down to within 10m of the surface. Three cases of strong hurricanes have been selected for this study, allowing analysis of these coefficients for conditions with up to 65 ms- 1 surface winds. The values of the drag coefficient, Cd, are demonstrated to reach a maximum value at about hurricane force, then maintain that value with higher wind speeds. The values of Ck, the heat flux coefficient, do not show variation with wind speed. These coefficients are calculated both at the standard 10m, so that they may be compared with existing literature, and at the top of the boundary layer, so that models which do not explicitly resolve the physics of the boundary layer may nonetheless make use of this data. The budget calculations in this study have shown that the 10m drag coefficient has a value of 0.0026 to 0.0030 for wind speeds in the 40-60 ms- 1 range. Eddy fluxes of total energy and entropy are also shown to be significant. With this effect added, budget calculations have shown that the 10m enthalpy transfer coefficient ranges from 0.0029 to 0.0036 under these conditions for Floyd and Georges. Thus, the ratio of Ck/Cd is slightly larger than 1.0. At the gradient wind level, Cd is 0.0019 ± 0.0010 and Ck is approximately 0.0018. / by William Douglas Ramstrom. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The main goal of the thesis is to characterize the attributes of conventional and unconventional reservoirs through passive seismicity. The dissertation is comprised of the development and applications of three new methods, each of which focuses on a different aspect of fractures/faults and the resulting seismicity. In general, the thesis work discusses reservoir characterization from two aspects: 1) understanding fractures and faults in reservoirs as seismic sources with induced seismicity, and then inferring other properties of the reservoirs, such as stress regime and velocity structure (Chapters 2, 3, 4); 2) understanding the fractures in reservoirs as seismic scatterers (Chapter 5). First, I introduce a new method to determine the source mechanisms of the induced earthquakes by incorporating high frequency waveform matching, first P-arrival polarities and average S/P amplitude ratios. The method is applied to 40 induced earthquakes from an oil/gas field in Oman monitored by a sparse near-surface seismic network and a deep borehole seismic network. The majority of the events have a strike direction parallel with the major NE-SW faults in the region, and some events trend parallel with the NW-SE conjugate faults. The results are consistent with the in-situ well breakout measurements and the current knowledge of the stress direction of this region. The source mechanisms of the studied events together with the hypocenter distribution indicate that the microearthquakes are caused by the reactivation of preexisting faults. Then I introduce a new method to locate microseismic events induced by hydraulic fracturing with simultaneous anisotropic velocity inversion using differential arrival times and differential back azimuths. We derive analytical sensitivities for the elastic moduli (Cij) and layer thickness L for the anisotropic velocity inversion. The method is then applied to a microseismic dataset monitoring a Middle Bakken completion in the Beaver Lodge area of North Dakota. Our results show: 1) moderate-to-strong anisotropy exists in all studied sedimentary layers, especially in both the Upper Bakken and Lower Bakken shale formations, where the Thomsen parameters (E and y) can be over 40%; 2) all events selected for high signal-to-noise ratio and used for the joint velocity inversion are located in the Bakken and overlying Lodgepole formations, i.e., no strong events are located in the Three Forks formation below the Bakken; 3) more than half of the strong events are in two clusters at about 100 and 150 meters above the Middle Bakken. Re-occurrence of strong, closely clustered events suggests activation of natural fractures or faults in the Lodgepole formation. Finally, I introduce a new hybrid method to model the shear (SH) wave scattering from arbitrarily shaped fractures embedded in a heterogeneous medium by coupling the boundary element method (BEM) and the finite difference method (FDM) in the frequency domain. The hybrid method can calculate scattering from arbitrarily shaped fractures very rapidly, thus Monte Carlo simulations for characterizing the statistics of fracture attributes can be performed efficiently. The advantages of the hybrid method are demonstrated by modeling waves scattered from tilted fractures embedded in complex media. Interesting behaviors of the scattered waves, such as frequency shift with the scattering order and coherent pattern of scattered waves through strong heterogeneities, are observed. This method can be used to analyze and interpret the scattered coda waves in the microseismic observations, e.g., the reverberating multiples in the Bakken microseismic data which cannot be explained by the determined layered anisotropic velocity model alone. / by Junlun Li. / Ph.D.