Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 175-181. / by Ellen Dunning Brown. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, September 2011. / "September 2011." Cataloged from PDF version of thesis. / Includes bibliographical references. / The five geologic studies presented in this thesis document how the recycling of tectonic plates at subduction zones has a profound effect on the melting behavior of the Earth's mantle. Two experimental studies (Chapters 1 and 2) of the melting behavior of mantle peridotite demonstrate that the forefathers of arc magmas are formed at extremely low temperatures in the mantle wedge at convergent plate margins in the presence of excess H²O or following the breakdown of the hydrous mineral chlorite. A new petrologic model that simulates anhydrous melting of variably metasomatized upper mantle is developed to investigate the petrogenesis of primitive basaltic lavas erupted in continental back-arc and ocean island settings (Chapter 3). This model suggests that <10.5 Ma anhydrous basaltic lavas erupted east of the Cascades arc were formed by mantle upwelling near the lithosphere-asthenosphere boundary caused by plate subduction, not by a mantle plume (Chapter 4). A geodynamic and petrologic study (Chapter 5) of asthenospheric flow at the margins of thick continental lithosphere reveals small degree melts of the mantle may be responsible for the large negative gradient in seismic wave speed observed at the lithosphere-asthenosphere boundary below eastern North America. These studies together advance our knowledge of how the recycling of tectonics plates on Earth affects melt generation in the Earth's mantle and subsequently the unique differentiation of our planet. / by Christy Berna Till. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003. / Includes bibliographical references (leaves 75-77). / An analytic study was performed to examine the effect of the stratosphere on the surface of the earth. The method of piecewise potential vorticity inversion was employed in the diagnosis of the magnitude of and dynamics behind the stratosphere-surface link in both the transient and stationary cases. The potential vorticity inversion results in both the transient and stationary models indicated that the stratosphere possesses a significant effect at the surface of the earth. It was determined that, compared to the stratosphere as a whole, it was primarily the lower stratosphere that had the most significant impact at the surface of the earth. The results of this analytic study therefore indicate that in modeling the surface of the earth, the dynamics detailed here between the lower stratosphere and surface must be included for the modeled surface weather or climate simulations to be accurate. / by Irene W. Lee. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986. / Microfiche copy available in Archives and Science / Bibliography: leaves 53-54. / by Ernest L. Hardin III. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1988. / Includes bibliographical references. / by Anne Victoria Judge. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Title as it appears in the M.I.T. Graduate List, Feb. 1992: Diurnal cycle of deep cloud cover in tropics. / Includes bibliographical references (leaf 53). / by Sewon Park. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and Woods Hole Oceanographic Institution, 1986. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN / Vita. / Includes bibliographies. / by Arthur J. Spivack. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. / Includes bibliographical references (leaves 60-61). / Numerical solutions of the unstable, growing modes are found for the two-layer inviscid quasigeostrophic equations in a meridional channel. A steady mean flow in the N-S direction is imposed in the upper layer, and it is assumed that changes in planetary vorticity following this mean flow are balanced by the input of vorticity from an imposed wind stress curl. Thus in the two-layer system, the vertical shear, in thermal wind balance, is associated with an interface slope which provides a gradient of potential vorticity (PV) in the x-direction, of equal magnitude and opposite sign in the two layers. In the y-direction the PV gradient has the value of planetary beta, [beta], in both layers. The unstable modes of this system exhibit a boundary-layer structure across the channel. They are intensified in the west. The growth rates of the unstable modes are of the same order as the zonal case, however the range of wavenumber and shear for which instability is possible is larger. Established cutoff criteria for the equal-layer zonal case are not applicable, and no analogous criteria has yet been found. Growing modes are found even for very weakly sheared flows, and this suggests that baroclinic instability may represent a more significant source of mid-ocean eddy energy than previously believed. / by Alison Walker. / S.M.

Thesis: Ph. D. in Climate Physics and Chemistry, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 113-119). / In this thesis we explore the role of the large-scale ocean circulation in the North Atlantic and the Southern Ocean (SO) in setting the regional and globally averaged sea surface temperature (SST) response to atmospheric forcing. We focus on the impact of anthropogenic greenhouse gases (AGHGs) and the Antarctic ozone hole and use output from general circulation models (GCMs) to estimate the corresponding climate response functions (CRFs). We show that the strength and the vertical extent of the time-mean Atlantic Meridional Overturning Circulation (AMOC) set the effective heat capacity of the World Ocean and affect the global CRF to greenhouse gas (GHG) forcing. A large fraction of the anomalous surface heat uptake induced by GHGs takes place over the North Atlantic. However, the SO also plays a significant role in removing excess heat from the atmosphere. Compared to the rest of the World Ocean, the SO warms at a much slower rate under GHG forcing. In this region the background Meridional Overturning Circulation (MOC) upwells unmodified deep water masses to the surface where they take up atmospheric heat. The modified water masses are then advected northward and subducted in the mid-latitudes. This geographical imprint of the MOC is reflected in the regional CRFs to GHGs, as seen in idealized numerical experiments with GCMs. However, GHGs are not the only major source of anthropogenic forcing on the SO. Stratospheric ozone depletion around Antarctica gives rise to an atmospheric pattern similar to the positive phase of the Southern Annular Mode (SAM): a strengthening and a southward shift of the westerlies. This poleward intensification of the winds changes the ocean circulation and gives rise to an SST response. We examine the SO CRF to a SAM pattern that arises either in the form of natural variability in unforced control experiments or as a result of imposed ozone perturbations. We analyze the SO SST response to SAM on multiple timescales and across an ensemble of GCMs from the Climate Modeling Intercomparison Project phase 5 (CMIP5). We show that the corresponding SO CRF is governed by the anomalous wind-driven MOC redistributing the background heat reservoir. The intermodel diversity in the fast and slow SST responses to SAM is partly explained by differences in the climatological thermal stratification across the ensemble of GCMs. Furthermore, we demonstrate that the sea ice response to SAM in models is very well correlated with the geographic pattern of the SST anomalies. Finally, we convolve our estimated CRFs with timeseries of historical forcing to recover the SO SST trends in numerical simulations and in observations. We contrast the multidecadal SO cooling trends against the SST warming rate in the Northern Hemisphere high latitudes. Our results imply that the recent cooling in the SO may be explained by the Antarctic ozone hole projecting on a positive SAM trend. We furthermore attempt to understand why CMIP5 models have been unable to reproduce the observed negative SST trends in the SO and instead predict regional warming. Many GCM simulations underestimate the historical SAM evolution. Another subset of CMIP5 models have biases in their climatological SO stratification, which affects their SO CRFs to SAM. The successful application of the CRF framework in the context of observed and simulated SST trends validates the results of our analysis. We are thus able to interpret the CRFs as inherent characteristics of the climate system and elucidate the importance of the high latitude oceans in transient climate change. / by Yavor Kostov. / Ph. D. in Climate Physics and Chemistry

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 245-254). / Atmospheric hydrogen (H₂ ), an indirect greenhouse gas, plays a notable role in the chemistry of the atmosphere and ozone layer. Current anthropogenic emissions of H₂ are substantial and may increase with its widespread use as a fuel. The H₂ budget is dominated by the microbe-mediated soil sink, and although its significance has long been recognized, our understanding is limited by the low temporal and spatial resolution of traditional field measurements. This thesis was designed to improve the process-based understanding of the H₂ soil sink with targeted field and lab measurements. In the field, ecosystem-scale flux measurements of atmospheric H₂ were made both above and below the forest canopy for over a year using a custom, automated instrument at the Harvard Forest. H₂ fluxes were derived using a flux-gradient technique from the H₂ concentration gradient and the turbulent eddy coefficient. A ten-fold improvement in precision was attained over traditional systems, which was critical for quantifying the whole ecosystem flux from small H2 concentration gradients above the turbulent forest canopy. Soil uptake of atmospheric H₂ was the dominant process in this forest ecosystem. Rates peaked in the summer and persisted at reduced levels in the winter season, even across a 70 cm snowpack. We present correlations of the H₂ flux with environmental variables (e.g., soil temperature and moisture). This work is the most comprehensive attempt to elucidate the processes controlling biosphere-atmosphere exchange of H₂ . Our results will help reduce uncertainty in the present-day H₂ budget and improve projections of the response of the H₂ soil sink to global change. In the lab, we isolated microbial strains of the genus Streptomyces from Harvard Forest and found that the genetic potential for atmospheric H₂ uptake predicted H₂ consumption activity. Furthermore, two soil Actinobacteria were found to utilize H₂ only during specific lifecycle stages. The lifecycle of soil microorganisms can be quite complex as an adaptation to variable environmental conditions. Our results indicate that H₂ may be an important energetic supplement to soil microorganisms under stress. These results add to the understanding of the connections between the environment, organismal life cycle, and soil H₂ uptake. / by Laura Kelsey Meredith. / Ph.D.