Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995. / Includes bibliographical references (leaves 316-326). / by Alison Marguerite Macdonald. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2003. / Cataloged from PDF version of thesis. Page 21 missing from original thesis. / Includes bibliographical references (pages 27-28). / We investigate the shape of Pluto's atmosphere using data from the occultation of the V=15.7 star P131.1 by Pluto on 2002 Aug 21 (UT). We find that Pluto's atmosphere, as projected onto the sky, is noticeably non-circular. This implies an overall ellipsoidal shape, which could be an indication of high winds and/or latitudinal stratification. We decide to compare our results to those obtained from datasets of the occultation of P8 by Pluto on 1988 June 9 (UT). Previous analyses of these datasets by Millis et al. (1993) had led to the conclusion that Pluto's atmospheric shape did not deviate from that of a sphere. However, we find that the 1988 datasets do not conclusively demonstrate that this is the case. We conclude that Pluto's atmosphere is currently non-spherical and could have been non-spherical at the time of the 1988 occultation. Implications for high winds and/or latitudinal stratification present exciting possibilities to be investigated by the upcoming New Horizons mission to Pluto. / by Colette Salyk. / S.B.

Thesis (Sc. D. in Climate Physics and Chemistry)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004. / Includes bibliographical references (p. 229-245). / This thesis revolves about the relationship between orbital forcing and climate variability. To place paleo and modern climate variability in context, the spectrum of temperature variability is estimated from time-scales of months to hundreds of thou- sands of years using a patchwork of proxy and instrumental records. There is an energetic background continuum and rich spatial structure associated with temperature variability which both scale according to simple spectral power-laws. To complement the spatial and temporal analysis of temperature variability, a description of the full insolation forcing is also developed using Legendre polynomials to represent the spatial modes of variability and singular vectors to represent seasonal and long-term changes. The leading four spatial and temporal modes describe over 99% of the insolation variability making this a relatively simple and compact description of the full insolation forcing. Particular attention is paid to the insolation variations resulting from the precession of the equinoxes. There is no mean annual insolation variability associated with precession - precession only modulates the seasonal cycle. Nonlinear rectification of the seasonal cycle generates precession-period variability, and such rectification naturally occurs in the climate system but also results from the seasonality inherent to many climate proxies. One must distinguish this latter instrumental effect from true climate responses. Another potential source of spurious low-frequency variability results from the stretching and squeezing of an age-model so that noise in a record is made to align with an orbital signal. / (cont.) Furthermore, and contrary to assertions made elsewhere, such orbital-tuning can also generate an eccentricity-like amplitude modulation in records that have been narrow-band-pass filtered over the precession bands. An accurate age-model is the linchpin required to connect insolation forcing with any resulting climatic responses, and to avoid circular reasoning, this age-model should make no orbital assumptions. A new chronology of glaciation, spanning the last 780 kilo-years, is estimated from 21 marine sediment cores using a compaction corrected depth scale as a proxy for time. Age-model uncertainty estimates are made using a stochastic model of marine sediment accumulation. The depth-derived ages are estimated to be accurate to within L9, 000 years, and within this uncertainty are consistent with the orbitally-tuned age estimates. Nonetheless, the remaining differences between the depth and orbitally derived chronologies produce important differences in the spectral domain. From the 6180 record, using the depth-derived ages, evidence is found for a nonlinear coupling involving the 100KY and obliquity frequency bands which generates interaction bands at sum and difference frequencies. If an orbitally-tuned age-model is instead applied, these interactions are suppressed, with the system appearing more nearly linear. A generalized phase synchronization analysis is used to further assess the nonlinear coupling between obliquity and the glacial cycles. Using a formal hypothesis testing procedure, it is shown that glacial terminations are associated with high obliquity states at the 95% significance level. The association of terminations with eccentricity or precession is indistinguishable from chance. / (cont.) A simple excitable system is introduced to explore potential mechanisms by which obliquity paces the glacial cycles. After tuning a small number of adjustable parameters, the excitable model repro- duces the correct timing for each termination as well as the linear and nonlinear features earlier identified in the 6180 record. Under a wide range of conditions the model exhibits a chaotic amplitude response to insolation forcing. One chaotic mode gives a train of small and nearly equal amplitude 40KY cycles. Another mode permits ice to accumulate over two (80KY) or three obliquity cycles (120KY) prior to rapidly ablating and thus, on average, generates 100KY variability. The model spontaneously switches between these 40 and 100KY chaotic modes, suggesting that the Mid-Pleistocene Transition may be independent of any major shifts in the background state of the climate system. / by Peter Huybers. / Sc.D.in Climate Physics and Chemistry

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 97-100. / by Rosamond Joyce Kinzler. / M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 49-52). / The Arctic atmosphere is especially sensitive to changes in climate forcing; however, Arctic processes and feedbacks are not understood well enough to accurately predict how the Arctic environment might change under anthropogenic forcing. Further study of the basic atmospheric processes is needed, especially due to uncertainties in modeling cloud feedbacks. August and September are the months when the Arctic sea surfaces begin to freeze; clouds play an important role in determining when this process begins. In this study, the radiative properties of Arctic stratocumulus are studied by comparing measurements for two days in August 2008 during the Arctic Surface Cloud Ocean Study (ASCOS) with simulations using the Rapid Radiative Transfer Model (RRTM). Cloud radiative forcing for both days is examined, and the modeled radiative fluxes were found to compare well to observations. Sensitivity studies are conducted on single and multi-level stratocumulus clouds to study their radiative interactions with each other. Cloud-top cooling in upper clouds is found to radiatively turn off cloud-top cooling in clouds below it. The RRTM and the surface radiative observations are used together to constrain estimates of liquid droplet radius; constraining these radii shows the sensitivity of shortwave cloud radiative forcing and the insensitivity of long wave cloud forcing to changes in drop size. / by Elizabeth A. Maroon. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Includes bibliographical references (leaves 16-17). / The Hellenides of Greece have undergone a series of extensional deformation events from early Miocene to present time. Two of the fault systems that accommodate this deformation in central Greece are the Itea-Amfissa detachment and the Parnassos detachment. The Itea-Amfissa detachment is known to have been active during Middle Miocene (Langhian and Serravallian time) from dating of marine sediments within the syn-tectonic hanging wall basin. The Parnassos detachment is probably younger, based on the Lower Pliocene sediments deposited in the hanging wall, but stratigraphically lower sediments are undated. The North Giona fault extends east-west from near the northern end of the Itea-Amfissa detachment to near the northern end of the Parnassos detachment. This steeply north-dipping normal fault probably truncates the Itea-Amfissa detachment, and approaches the Parnassos detachment in an area where the topography is low and highly irregular, suggesting that it may connect to and absorb some of the motion along the Parnassos detachment. Structural mapping in this area between the North Giona fault and the Parnassos detachment demonstrates that the limestone and flysch of the Parnassos nappe are folded without significant faulting. Folds occur in two orientations; the northwest-oriented structures are older and are probably related to nappe emplacement; the younger, east-west trending folds are probably related to Late Cenozoic extension. The lack of through-going faults indicates that the North Giona fault and the Parnassos detachment do not connect. Structural relations also show that the Parnassos detachment is younger than the east-west trending fold structures within the field area, and also probably younger than the North Giona fault. / by Erika Swanson. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993. / GRSN 640468 / Includes bibliographical references (leaves 204-214). / by Carl Takeo Friedrichs. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 213-230). / This dissertation describes the most comprehensive study to date of the diurnal cycle of air pollution in the Kathmandu Valley, Nepal -- a bowl-shaped mountain valley of two million people with a growing air pollution problem but little past research. Field measurements and computer simulations were used to study the interplay of emissions and ventilation. From September 2004 through June 2005, CO (carbon monoxide), ozone, PM10 (particles smaller than 10 micrometers), wind speed and direction, solar radiation, temperature, and humidity were continuously measured east of Kathmandu. Sensors towers and mountains measured the diurnal cycle of the vertical temperature structure and stability. A sodar measured the mixed layer height and upper-level winds. Bag sampling provided the diurnal cycle of CO on mountains, passes and around the valley. Winds were measured on a mountain pass and ozone on a mountaintop. Patterns of air pollution and meteorology in the valley showed remarkable day-to-day similarity, with daily twin peaks of CO and PM10, a noon ozone maximum, afternoon westerly winds, and a stagnant cold pool at night. On mountaintops at night, ozone remained high, while CO dropped to regional background levels. / (cont.) The meso-scale meteorological model MM5 was adapted to the Kathmandu Valley for days in February and May 2005. It was able to capture the essential features of the valley's meteorology and was used to address three specific questions: The break-up of the valley's temperature inversion was found to be dominated in February by up-slope winds on the valley rim, plus subsidence over the valley center; in May surface heating of the valley bottom also played a major role. The pathways of pollutant transport out of the valley were found to be up the valley rim slopes in the morning, but out the eastern and southern passes in the afternoons. At night pollutants remained within the valley except near the river outlet. They were lifted off the ground at night and re-circulated in the morning. The eulerian chemistry transport model CAMx, was used in tracer mode, with MM5 meteorology to simulate the emission, transport and removal of CO from the Kathmandu Valley. The simulations were limited by the accuracy of Kathmandu's emissions inventory, especially the spatial distribution of emissions. / by Arnico K. Panday. / Sc.D.

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

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 77-78). / General relativity, though widely accepted in the weak-field limit, is difficult to test in the strong-field regime. Millimeter wavelength VLBI offers a unique opportunity to resolve the black hole structure on event-horizon scales. The ability of millimeter wavelength VLBI observations of Sgr A* to constrain black hole parameters such as mass, spin, and deviation from general relativity was considered. Realistic simulations of Sgr A* were performed using the MAPS software. Image reconstructions were made using MACIM and image-based parameter extraction using the Hough transform was considered. Non-imaging techniques using least-squares fitting of a simple ring and gaussian model to VLBI amplitudes and closure phases were considered. The Hough transform is not able to place strong constraints on black hole parameters. Least-squares fitting techniques indicate possible sensitivity to deviations from general relativity and prove able to extract the photon ring radius to within 5-7% of the expected value. It is concluded that VLBI observations of Sgr A* represent a promising opportunity for testing general relativity in the strong-field regime. / by Jessica Dawn Ruprecht. / S.B.