Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1987. / Bibliography: leaves 52-53. / by Virginia Ann Fry. / M.S.

Thesis: Ph. D. in Atmospheric Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 103-114). / Spiral bands are one of the most prominent features of tropical cyclones (TCs). These regions of clouds and rainfall are often the source of major TC hazards, such as inland flooding, mudslides, and tornadoes. Since the advent of radar technology, numerous ideas have been proposed to explain the existence of TC spiral bands. Previous hypotheses include the manifestation of atmospheric waves emanating from the TC inner core, boundary layer instabilities, and the interaction between surface cold pools and low-level vertical wind shear. Despite much effort, no consensus has yet been reached on the underlying physical mechanism responsible for TC bands. We approach this problem by examining the formation of TC spiral bands in a set of idealized three-dimensional simulations from the System for Atmospheric Modeling. / The simulations are run with doubly-periodic horizontal boundaries, fixed sea surface temperature (300-301K), interactive surface fluxes, and a constant rotation rate corresponding to latitude 15N. No background mean flow is imposed on the TC runs. We find that, in simulations with full moist physics and interactive radiative fluxes, spiral bands are consistently collocated with surface cold pools and aligned normal to the low-level wind shear, similar to tropical squall-lines. However, convection still organizes into spiral bands in simulations in which surface cold pools are supressed. Non-rotating experiments with imposed background wind shear taken from a TC simulation suggest that, in the absence of surface cold pools, vortex dynamics are necessary for convection to align into spiral bands. Finally, we examine numerical simulations of TC-like vortices that develop over a completely dry surface. / We find that these dry TCs also exhibit many spiral bands in the wind and temperature fields extending far away from the inner core. Initially, these perturbations are nearly stationary and exhibit overturning circulations consistent with boundary layer instabilities. Barotropic-baroclinic instability dominates the TC structure later in the simulation, reducing the outer region to just a few spiral bands. / by Diamilet Perez-Betancourt. / Ph. D. in Atmospheric Science / Ph.D.inAtmosphericScience Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 227-251). / The spatiotemporal variability of water vapor near the Equator remains poorly understood because convective organization simultaneously spans the cloud scale (~ 10km) and the planetary scale (~ 10, 000km). Spatiotemporal variability of tropical water vapor may result from internal instabilities of the atmosphere, arising from the interaction between water vapor, radiation and convection. The present work leverages the instability of radiative-convective equilibrium, the most fundamental state of the tropical atmosphere, to connect convective organization in cloud-permitting models with the observed variability of water vapor through common physical mechanisms. First, we propose a simple theory that explains when instability of radiative-convective equilibrium may occur: If the total atmospheric cooling decreases with column water vapor, then radiative-convective equilibrium may be unstable to the growth of moist and dry perturbations. / Secondly, we combine a linear response framework with the weak temperature gradient approximation to analyze the interaction between convection, radiation and water vapor at each level of the atmosphere. We find that convection may interact with radiation to trigger the growth of mid-tropospheric water vapor anomalies by transporting water vapor to the upper troposphere, where it can prevent lower-tropospheric water vapor from radiatively cooling to space. Thirdly, we turn to the spatial organization of water vapor anomalies and relate the evolution of the size of moist and dry regions to diabatic fluxes in twenty cloud-permitting simulations on large domains. Longwave radiation from ice clouds aggregates convection at larger scales, shortwave radiation aggregates convection at smaller scales, and surface enthalpy fluxes smooth out water vapor anomalies through their enthalpy disequilibrium component. / Finally, we relate the transient zonal variability of precipitable water to convective-aggregation mechanisms in realistic models and observations of the atmosphere. Radiative fluxes generate transient water vapor structures of planetary scales, while surface enthalpy fluxes and horizontal energy transport act to smooth out these structures, suggesting parallels between observations and idealized simulations of aggregated convection. / by Tom Beucler. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: Ph. D. in Geology, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis presents a multidisciplinary investigation of the processes and timescales for the construction of arc crust, with a focus on the exposed crustal section in the southernmost Sierra Nevada Batholith, California. This section exposes plutons that were emplaced at pressures ranging from 3-10 kbars, as well as metamorphic wall rocks. Chapters 1 and 2 represent focused studies of the Bear Valley Intrusive Suite (BVIS), the dominant igneous component of the crustal section. Chapter 1 presents new magmatic structural data and whole rock geochemical data that highlight a discontinuity in the BVIS between a lower crust dominated by originally shallowly lying mafic cumulates and an upper crust dominated by steeply oriented felsic intrusives. These observations are used to constrain the thermal state of the arc during the emplacement of the BVIS. Chapter 2 is a high-precision CA-ID-TIMS U/Pb zircon geochronology study of the BVIS. / This study shows that the entire BVIS was emplaced within 1.1 million years, and thus represents the highest documented (intrusive) subduction zone magmatic flux. Chapter 3 focuses on the contribution of the metamorphic wall-rocks to the observed crustal section. Using detrital zircon geochronology, I argue that these wall-rocks preserve an inverted stratigraphy that is most easily explained if these sediments were first subducted and subsequently returned as relaminated material, which would make these materials the first in situ example of relaminated sediments. Chapters 4 and 5 present broader studies of subduction zone processes in space and time. In Chapter 4, I present a study based on a global compilation of modern arc lavas. / This study develops new proxies that use distinctive major element trends produced by fractionating magmas to qualitatively constrain the hydration state and initial fractionation pressure of differentiating magmas, and finds that magmas in continental arcs typically evolve at wetter and higher-pressure conditions compared to island arcs. Finally, Chapter 5 investigates the dynamics of subducted slabs through Earth's history and finds that, based on anticipated higher mantle temperatures and concomitant thicker, more mafic oceanic crust, subducted slabs in the Archean are unlikely to have stagnated within or immediately below the mantle transition zone. / by Benjamin Zachary Klein. / Ph. D. in Geology / Ph.D.inGeology Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmosphere and Planetary Sciences, 1987. / Bibliography: leaves 88-89. / by Elizabeth Burch Welsh. / M.S.

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