Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (p. 205-214). / Studies of the response of ice sheets to climate change require data sets with high accuracy and uniform ice-sheet coverage. The most common technique used in analyzing satellite altimetry data to study height change in the ice sheets is the dH/dt technique based on the cross-over geometry. In this thesis two alternative techniques to cross-overs are studied and applied to all ERS radar and ICESat laser altimetry data to study height change in Antarctica. The first technique, block kriging, uses all available data to build a statistical model of the elevation field. Results of height rate of changes dh/dt ill Antarctica for the years 1995-2001 produced using block kriging and cross-over analysis are compared. In the Amery Ice Shelf and in the West Antarctic coastal area and near latitude -81°N, the difference in dh/dt between the two methods are statistically significant. A second technique combines kriging and Kalman filtering to allow for time evolutions of the height change rate and other parameters used in the description of the surface elevation field. An application of the technique to laser altimetry data from the current NASA's ICESat mission shows the potential of the technique in detecting height change. / (cont.) In addition, the method can potentially characterize surface elevation in Antarctica at small horizontal scales of the order of the laser footprint size. The quality of laser altimetry data at the present is not sufficient for height change detection at the accuracy level of 2cm/yr required for studying mass balance in Antarctica. / by An Thanh-Thuy Nguyen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003. / Includes bibliographical references (p. 132-144). / This work provides a statistical description of the near-Earth asteroids (NEAs) in terms of number, orbital parameters, reflectance spectra, albedos, diameters, and terrestrial and lunar collision rates. I estimate the size and shape of the NEA population using survey data from the Lincoln Near-Earth Asteroid Research project including more than 1300 NEA detections. The NEA population is more highly inclined than previously estimated and the total number of NEAs with absolute magnitudes (H) brighter than 18 is 1227 +170/-90. The absolute magnitude and orbital parameter distributions for the NEAs are combined with reflectance spectra and albedo measurements. I obtain a debiased estimate of the fraction of NEAs in each of 10 taxonomic complexes, and a debiased average albedo for each. The number of NEAs larger than 1 km is 1090 +/- 180. Next, I determine the impact frequency, collision velocity distribution and collision energy distribution for impacts of NEAs into the Earth and Moon. Globally destructive collisions ([approx.] 1021 J) of asteroids 1 km or larger strike the Earth once every 0.60 +/- 0.1 Myr on average. Regionally destructive collisions with impact energy greater than 4x1018 J ([approx.] 200 m diameter) strike the Earth every 47,000 +/- 6,000 years. The rate of formation of craters expected from the NEAs is found to be in close agreement with the observed number of craters on the Earth and Moon. / (cont.) These results combine the largest set of NEA discovery statistics from a single survey, the largest set of physical data on NEAs, and corrections for observational bias. The result is a comprehensive estimate of the total NEA population in terms of orbital parameters, absolute magnitudes, albedos, and sizes. This improved description of the NEAs will help us to plan surveys to find and study the remaining undiscovered NEAs, to connect the NEAs to their origins in the main-belt, to connect the NEAs to meteorite samples, to compare the lunar and terrestrial cratering record to the current population of potential impactors, and to understand the magnitude of the NEA impact hazard to the Earth's biosphere. / by Joseph Scott Stuart. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1987. / Microfiche copy available in Archives and Science. / Bibliography: leaves 197-204. / by Wesley Nobuo Ebisuzaki. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000. / Includes bibliographical references. / The study of Streaming potentials has applications in the earth sciences, ranging from fluid flow monitoring, to permeability determination, to studying the surface chemistry of rocks and minerals. In this thesis study of frequency-dependent electrokinetics is presented with both theoretical development and experimental verification. The complex (real and imaginary) streaming potential coupling coefficient is explained. This is followed by the first experiments to measure the real and imaginary part of frequency-dependent streaming potential coupling coefficients. As part of this study an experimental apparatus and data acquisition system were constructed to measure the streaming potential coupling coefficients as a function of frequency. The purpose of the experiments was to measure, for the first time, the real and imaginary part of streaming potentials. In addition, the measured frequency range was extended beyond any previous measurements. Frequency-dependent streaming potential experiments were conducted on one glass capillary, two porous glass filters, and one rock. The sample pore diameters ranged from 34 micrometers to 1 millimeter. Without these experiments, the validity of modeling of the frequency dependence of the seismoelectric effect using existing models streaming potential models would be in question. Two frequency- dependent models (Packard and Pride) were compared to the data. Both Pride's and Packard's models have a good fit to the experimental data in the low and intermediate frequency regime where viscous terms dominate in the fluid. In the high frequency regime, where inertial terms start to dominate, the data fits the theory after being corrected for capacitance effects of the experimental setup. Pride's generalized model appears to have the ability to more accurately estimate pore sizes in the porous medium samples. Packard's model has one unknown model parameter whereas Pride's model has four unknown model parameters, two of which can be independently determined experimentally. Pride's additional parameters may allow for a determination of permeability. As part of the study of frequency-dependent electrokinetics, this thesis presents the theory for frequency-dependent electro- osmosis. It is shown that the electro- osmosis frequency-dependent coupling coefficient is constant with increasing frequency until the critical frequency is reached, at which point the coupling coefficient starts to decrease with increasing frequency. The frequency response- electro- osmosiso- osmosis coupling coefficient is dependent on the capillary radius. The smaller the capillary radius the higher the critical frequency. Data is presented for a 0.127 mm capillary. In addition to studying frequency-dependent electrokinetics, this thesis examines the temperature-dependent behavior of streaming potential coupling coefficients. As part of this examination a review is made of the previous literature that discusses the temperature dependence of streaming potentials. The streaming potential coupling coefficient is determined using the permittivity, the conductivity, and the viscosity of the fluid. It has been determined that the temperature-dependent behavior of the permittivity, conductivity, and viscosity are well documented and do not alone account for temperature dependence of streaming potentials. The other quantity used in calculating the streaming potential coupling coefficient is the zeta potential. The temperature dependence of the zeta potential is not well understood at the present time. By examining the theory, it appears that the zeta potential temperature dependence is controlled by the fluid concentration and the adsorption properties of the surface. After examining the theory, streaming potential experiments at elevated temperature and pressure were conducted on Fontainebleau Sandstone, Berea Sandstone, and Westerly Granite. The experiments were conducted in a pressure vessel with temperatures ranging from 23° C to 200° C at pore pressure ranging from 20 bar to 50 bar and confining pressures ranging from 200 bar to 250 bar. The zeta potential was found to increase with increasing temperature, and the coupling coefficient can increase or decrease depending on how the conductivity of the sample varies. This implies that in geothermal regions, streaming potentials can have large magnitudes depending on the conductivity of the geothermal fluid. / by Philip M. Reppert. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 378-403. / by Eric Allen Bergman. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 171-184). / Increased industrialization and human activity modified the atmospheric aerosol composition and size-distribution during the last several decades. This has affected the structure and evolution of clouds, and precipitation from them. The processes and mechanisms by which clouds and precipitation are modified by changes in aerosol composition and size-distribution are very intricate. The objective of this thesis is to improve the understanding of the processes and mechanisms through which the changes in aerosol concentrations impact the evolution of deep convective clouds and precipitation formation. We develop a new coupled model in which a very detailed model of aerosol activation is coupled to a three-dimensional cloud resolving model. This coupled model can accurately represent different kinds of aerosol populations. This coupled model is used to investigate the impact of changing aerosol concentrations on the dynamics, microphysical evolution and precipitation formation in deep convective clouds. We examine the theories of aerosol activation, and the representation of aerosol activation in cloud models. The limitations of the extant methods of representation of aerosol activation in cloud models are evaluated. Then we descibe the components of the coupled model - Modified Eulerian and Lagrangian Aerosol Model (MELAM) and the Cloud Resolving Model (CRM). The features of these two component models with respect to aersol activation and cloud formation are discussed. The evaluation of the coupled model by simulation of a deep convertive event observed during the INDian Ocean EXperiment (INDOEX) by statistcal comparison of observed and simulated cloud fields shows that the coupled model can simulate deep convective events reasonably well. We present a study of the senstivity of the model to initial thermodynamic conditions (CAPE). Different initial thermodynamic conditons sampled during the INDOEX are used to initialize the coupled model and, the structure and evolution of the deep convective event are discussed. The study sheds new light on the respone of deep convection to CAPE. It is found that when the atmosphere has moderate CAPE, the precipitation forming processes are very active and when the CAPE is (cont.) low or high, they are comparatively less efficient. / As the most important part of our study, we examine the response of deep convection to changing initial aerosol concentration. Different aerosol concentrations from those representing pristine to polluted atmospheres are considered. We look at the buoyancy of the cloud and the microphysical evolution. It is found that the dynamics and microphysics are tightly coupled and we infer that to understand aerosol-cloud interactions in deep convective clouds, both - dynamics and microphysics - and their interaction have to be taken into consideration. Our results show that the response of a deep convective cloud to changing aerosol concentration is very different from the much well understood reponse of shallow clouds or small cumulus clouds. In general, increase in aerosol concentratin is seen to invigorate convection and lead to greater condensate. Although the cloud droplet size decreases, collision-coalescence is not completely inefficient. The precipitation in high aerosol regime is seen to occure in short spells of intense rain. A very interesting anomalous response of deep convection to initial aerosol concentration is observed at intermediate aerosol concentrations. The cloud lifetime, and precipitation are seen to increase in this regime. A possible mechanism to explain this anomalous behavior is proposed and the available circumstantial support for the mechanism from extant observations is presented. It is proposed that the efficient collection of rain and cloud droplets by ice and graupel particles in the middle troposphere is primarily responsible for this increased cloud lifetime and precipitation. / by Udaya Bhaskar Gunturu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / 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. / Radioisotopic dating can provide critical constraints for understanding the rates of tectonic, dynamic and biologic processes operating on our planet. Improving the interpretation and implementation of geochronologic data by coupling it with numerical modeling studies is the central theme of this thesis. Each chapter works to address a variety of problems in the Earth sciences. In each study, the interpretation of geochronologic data is aided with a numerical model that simulates the long-term behavior and/or initial conditions of the U-Pb system and provides an effective means of exploring the parameters that influence a calculated date. The record provided by geochronologic data is then coupled with models to quantitatively determine rates of geologic process on Earth. This approach permits geochronologic data to move beyond just establishing a relative time line of events. Using this dual modeling approach, Chapters 2-5 work to measure the long-term cooling and erosion rate of the lithosphere, specifically constraining the time scales and rate of transition between the stages of mountain belt formation and stability. Chapter six works to constrain the timing and duration of Central Atlantic Magmatic Province flood basalt volcanism and its relationship to the end Triassic mass extinction. The seventh and final chapter uses high precision U-Pb geochronology to evaluate the reliability of an Ar-Ar standard often used as a fluence monitor. The overall focus of this thesis has been to push the envelope of geochronologic precision and accuracy while coupling the data with modeling studies to yield new insight into Earth systems. / by Terrence Blackburn. / Ph.D.

Thesis (Ph. D. in Physical Biology)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 201-224). / The relationship between structure and function is a longstanding and central topic in biology, evolution, and ecology. The importance of morphology is clearly visible in the diverse forms taken by innumerable organisms in order to perform a myriad of functions. Examining the great variety of morphological characteristics it would seem that the overall principle of evolution is the only way to generalize the observed diversity: given differences in environments and random biological variation a great multitude of body plans have been invented as adaptations to many dynamic habitats given specific evolutionary histories. In this thesis I will show how focusing on diverse organisms makes it possible to identify common first-order laws of evolutionary organization. More specifically I will show how these common laws derive from a connection between organism structure, physical limitations, environmental constraints, and basic metabolic, biochemical, or energetic principles. Furthermore, I will show how this top level of biological organization holds significant predictive power for regional ecology and for interpreting the general trends of evolutionary history. In Chapter 2 we begin by deriving a model for the growth of single cells and populations of cells. This model is based on the partitioning of metabolic resources and the scaling relationship between metabolism and body size. We show that the growth of diverse classes of organisms is connected by common unit energetics. However there exist striking differences in the broad trends between growth rate and body size across these different classes and we show that this is a consequence of major evolutionary transitions which adjust the partitioning of metabolic resources. We interpret major evolutionary transitions to occur in response to energetic limitations. We also find that multicellular living for unicellular organisms provides a metabolic and reproductive advantage. In Chapters 3 and 4 we further investigate these features in microbial biofilms which exhibit rich spatial patterning. Using a mathematical model and experimentation we find that the tall vertical structures produced by these biofilms have optimal geometry for resource uptake and the growth efficiency of the entire colony. Our model allows us to predict the observed changes in feature geometry given alterations to the environmental conditions that the biofilms are grown in. Furthermore, we are able to show that the morphology of these structures is dependent on single cell physiology. For example, single genetic knockouts of flagellar motility radically alter the temporal dynamics of feature spacing. Our work highlights morphology as a central property in multicellular organisms which mediates the interaction between environmental conditions and physiology. In Chapter 5 we highlight the importance of morphology in complex multicellular life where we develop a general model of tree architecture which we link to physiological success within a given environment. Although this model is general, uses only tree size as a governing parameter, and does not consider speciation we are able use local resource availability to predict broad regional patterns in plant traits such as maximum tree height. Each of these chapters highlights the importance of structure and morphology at multiple biological scales. In Chapter 6 we show how the importance of structure extends to the genetic level where the specific encoding of a gene can have implicit information and functionality beyond the basic translation of codons. We investigate the observed implicit function of dramatic and frequent changes in the mutation rate of an organism given the structure of the mutL gene. We show mathematically that altering mutation rates is an evolutionarily advantageous strategy, and we show bioinformatically that the specific genetic structure that gives rise to this trait is under positive evolutionary selection. / by Christopher Andrew Poling Kempes. / Ph.D.in Physical Biology

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1988. / Includes bibliographical references. / by Michael Baldwin Baker. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 85-88). / The photometric precision needed to measure a transit of small planets cannot be achieved by taking observations from the ground, so observations must be made from space. Mid-sized nanosatellites can provide a low-cost option for building an optical system to take these observations. The potential of using nanosatellites of varying sizes to perform transit measurements was evaluated using a theoretical noise budget, simulated exoplanet-transit data, and case studies to determine the expected results of a radial velocity followup mission and transit survey mission. Optical systems on larger mid-sized nanosatellites (such as ESPA satellites) have greater potential than smaller mid-sized nanosatellites (such as CubeSats) to detect smaller planets, detect planets around dimmer stars, and discover more transits in RV followup missions. / by Rachel Bowens-Rubin. / S.M.