Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Includes bibliographical references (p. 225-234). / by Paul Edward Filmer. / Ph.D.

Thesis: Ph. D. in Atmospheric Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 173-189). / The influence of anthropogenic aerosol emissions on the optical properties of clouds and the radiative forcing arising from these interactions, known as the aerosol indirect effect on climate, constitutes a fundamental uncertainty in our understanding of 2 0 th century climate change. In this dissertation, we investigate the role of a keystone physical process, droplet activation, in contributing to this uncertainty. The first half of the ensuing work focuses on the parameterization of this process in global model, assessing both existing schemes and developing a novel one. The second half then quantifies the influence of activation by using a suite of aerosol-climate models which include a complete description of the physics which give rise to the indirect effect. Parameterizations of droplet activation perform well for idealized single-mode aerosol populations, but show systematic biases in high-pollution, weak-updraft regimes. These are exacerbated when the aerosol in question is a complex mixture. We show that estimates of droplet nucleation are highly sensitive to changes in the accumulation mode size and number concentration; this mode is itself sensitive to anthropogenic aerosol emissions, which potentially further biases modeled cloud droplet number. Using a model emulation technique, we develop a framework for building efficient metamodels of activation, which greatly reduce the mean error in droplet number predicted across regimes. The biases in these parameterizations raise questions the influence of activation on the indirect effect. Using different schemes, we calculate a spread of 1 W m- 2 in the indirect effect, which we show is equal to the spread computed from an independent suite of global models with different aerosol and physics modules. The estimated indirect effect scales more strongly with the baseline cloud droplet number concentration simulated by each model than by its change from pre-industrial to present day, indicating a strong saturation effect. While present-day estimates of aerosol-cloud interactions derived from satellite-based instruments are inadequate at constraining the pre-industrial cloud droplet burden, we show that process-based measurements could overcome this problem. / by Daniel Alexander Rothenberg. / Ph. D. in Atmospheric Science

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Includes bibliographical references (p. 82-86). / Ocean heat content change (ocean heat uptake) has an important role in variability of the Earth's heat balance. The understanding of which methods and physical processes control ocean heat uptake needs improvement in order to better understand variability in the Earth's heat balance, improve the simulation of present-day climate, and improve the understanding and projection of future climate. Wind stress can play a strong role in ocean heat uptake on all timescales, and short timescale wind stress effects have not been well studied in the literature. This study for the first time examines short timescale spatial and temporal patterns of global variable wind stress datasets in a coupled atmosphere-ocean climate model. NCEP wind stress dataset was characterized for years 1978 to 2007. NCEP monthly means and monthly standard deviations are of the same magnitude, and strong wind stress events (tropical cyclones) are observed. A variety of metrics cannot reliably identify significant timescales or spatial patterns of the variable wind stress. Model behavior with and without variable wind stress is studied. This study uses the MIT IGSM, a 4°x 11 vertical level zonal atmospheric model coupled at the four hour timestep to a 20x2.50x22 vertical level ocean model with the K profile parameterization. Ocean properties in a no forcing scenario are sensitive to variable wind stress. In a weak forcing scenario (observed forcing over the last century), ocean properties are sensitive to variable wind stress, and internal modes of variability (such as an equatorial Pacific oscillation) are observed. In a global warming scenario (1% CO2 rise per year or a business as usual emissions scenario), the strong forcing overwhelms the more subtle responses due to the differences in variable wind stress forcing. Regardless of forcing, the high frequency variable wind stress (monthly or less) variable wind stresses can force a low frequency response. Hence the major source of annual variability of the MOC in this coarse resolution model is surface wind variability. / by Kelly Klima. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Vita. / Bibliography: leaves 292-301. / by William R. Martin. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmosphere and Planetary Sciences, 1988. / Title as it appears in M.I.T. Graduate List, Sept. 1988: Comparison of model solar and infrared fluxes with aircraft-based radiometer measurements. / Includes bibliographical references. / by Ilana Rachel Stern. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The goal of this thesis is to understand how the functional traits of species, biotic interactions, and the environment jointly regulate the community ecology of phytoplankton. In Chapter 2, I examined Continuous Plankton Recorder observations of diatom and dinoflagellate abundance in the North Atlantic Ocean and interpreted their community ecology in terms of functional traits, as inferred from laboratory- and field-based data. A spring-to-summer ecological succession from larger to smaller cell sizes and from photoautotrophic to mixotrophic and ieterotrophic phytoplankton was apparent. No relationship between maximum net growth rate and cell size or taxonomy was found, suggesting that growth and loss processes nearly balance across a range of cell sizes and between diatoms and dinoflagellates. In Chapter 3, I examined a global ocean circulation, biogeochemistry, and ecosystem model that indicated a decrease in) phytoplankton diversity with increasing latitude, consistent with observations of many marine and terrestrial taxa. Ii the modeled subpolar oceans, seasonal variability of the environment led to the competitive exclusion of phytoplankton with slower growth rates and to lower diversity. The relatively weak seasonality of the stable subtropical and tropical oceans in the global model enabled long exclusion timescales and prolonged coexistence of multiple phytoplankton with comparable fitness. Superimposed on this meridional diversity decrease were "hot spots" of enhanced diversity in soc regions of energetic ocean circulation which reflected a strong influence of lateral dispersal. In Chapter 4, I investigated how small-scale fluid turbulence affects phytoplankton nutrient uptake rates and community structure in an idealized resource competition model. The flux of nutrients to the cell and nutrient uptake are enhanced by turbulence, particularly for big cells in turbulent conditions. Yet with a linear loss form of grazing, turbulence played little role in regulating model community structure and the smallest cell size outcompeted all others because of its significantly lower R* (the minimum nutrient requirement at equilibrium). With a quadratic loss form of grazing, however, the coexistence of many phytoplankton sizes was possible and turbulence played a role in selecting the number of coexisting size classes and the dominant size class. The impact of turbulence on community structure in the ocean may be greatest in relatively nutrient-deplete regions that experience episodic inputs of turbulence kinetic energy. / by Andrew David Barton. / 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 (p. 163-175). / Mesoscale eddies mix and transport tracers such as heat and potential vorticity laterally in the ocean. While this transport plays an important role in the climate system, especially in the Southern Ocean, we lack a, comprehensive understanding of what sets mixing rates. This thesis seeks to advance this understanding through three related studies. First, mixing rates are diagnosed from an eddy-resolving state estimate of the Southern Ocean, revealing a meridional cross-section of effective diffusivity shaped by the interplay between eddy propagation and mean flow. Effective diffusivity diagnostics are then applied to quantify surface mixing rates globally, using a, kinematic model with velocities derived from satellite observations; the diagnosed mixing rates show a rich spatial structure, with especially strong mixing in the tropics and western-boundary-current regions. Finally, an idealized numerical model of the Southern Ocean is analyzed, focusing on the response to changes in win( stress. The sensitivity of the meridional overturning circulation to the wind changes demonstrates the importance of properly capturing eddy mixing rates for large-scale climate problems. / by Ryan Abernathey. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 64-68). / The REgolith X-ray Imaging Spectrometer (REXIS), a Charge-Coupled Device (CCD)-based coded aperture soft X-ray (0.3-7.5 keV) telescope for remote geochemical X-ray Fluorescence (XRF) spectrometry, will be flying on board the Origins Spectral Interpretations Resource Identification Security Regolith Explorer (OSIRIS-REx) asteroid sample return mission that will be visiting the asteroid 1999 RQ36 and sending a sample back to Earth. REXIS will detect elemental XRF lines and produce a histogram of results as the spacecraft orbits the asteroid as well as produce a global map of elemental abundance ratios. The accuracy requirement for measuring the global ratios of elements and the spectral resolution requirement for discriminating unique XRF lines from each other have been set in place. The correct interpretation of X-ray measurements from the surface of 1999 RQ36 is limited by properties that are intrinsic to the CCD detector, CCID-41, that has been chosen for REXIS. This thesis study outlines student experimentation and results that were conducted on the CCID-41 detector to gauge the intrinsic detector noise as a function of detector temperature. Further, the widening of spectral lines on the resultant histogram was also equated as a function of detector temperature. Members of the REXIS Team built a spectral resolution model to investigate both the widening of spectral lines as a function of detector temperature and the accuracy of the measurement of elemental abundance line ratios as a function of detector temperature. Data from the student laboratory experimentation suggested that the detector temperature remain at or below -75°C to minimize intrinsic noise properties. Data from the computational analyses of the spectral resolution model suggest consistent results that the detector temperature remains at or below -55°C to remain within the established REXIS requirements. The combination of these three results leads to the author's recommendation that a detector temperature requirement be set that the temperature of the CCD detector onboard REXIS shall not exceed -55°C and that a detector temperature goal be set that the temperature of the CCD detector shall not exceed -75°C. / by Suzanna Megyery. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 283-306. / by Jennifer Lynn Hall. / 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 42-44. / by Michael H. Mellen. / M.S.