Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005. / Includes bibliographical references. / The 6000-km long, age-progressive linear Hawaii-Emperor Chain is one of the best defined hotspot tracks. This hotspot track plays an important role in the plume hypothesis. In this research, geochemical data on the Hawaiian-Emperor lavas are used to evaluate the plume hypothesis. There are important geochemical similarities among lavas from the Hawaii-Emperor Chain, such as high Ba/Th (>100), high ³He/⁴He (>10 R/R-A) and enrichment in incompatible elements. These distinctive geochemical characteristics are not present in mid-ocean ridge basalt (MORB). Consequently, it is inferred that a common mantle source has been contributing to the Hawaiian-Emperor volcanism for over 80 My, which provides the strongest geochemical argument supporting the plume hypothesis. The distinctive geochemical characteristics of Makapuu-stage Koolau lavas, such as high SiO₂ content, ⁸⁷Sr/⁸⁶Sr, ²⁰⁸Pb*/²⁰⁶Pb*, [delta]¹⁸0, ¹⁸⁷Os/¹⁸⁸Os, La/Nb, Sr/Nb and low CaO content, ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, Th/La, require that recycled ancient oceanic crust including sediments is present in the Hawaiian plume. Some of these distinctive geochemical characteristics are also present in other Hawaiian shields. For example, Kahoolawe lavas also range to low ²⁰⁶Pb/²⁰⁴Pb. / (cont.) However, Kahoolawe lavas are not characterized by relatively high SiO₂ content, Sr/Nb and La/Nb and low CaO content that are characteristic of Makapuu-stage Koolau lavas, and they are offset from other Hawaiian shield lavas to high ⁸⁷Sr/⁸⁶Sr at a given ¹⁴³Nd/¹⁴⁴Nd. Since Hawaiian shield lavas have similar Sr/Nd (variation less than a factor of three), I speculate that the ⁸⁷Sr/⁸⁶Sr offset is a result of varying roles of recycled plagioclase-rich gabbro in Hawaiian shield lavas. Modem Hawaiian volcanoes form two offset trends, i.e., the Loa and Kea trends. Lavas from Loa and Kea trends have important geochemical differences. Specifically, Loa trend lavas have relatively higher ²⁰⁸Pb/²⁰⁴Pb at a given ²⁰⁶Pb/²⁰⁴Pb than Kea trend lavas, that is, Loa trend lavas have higher ²⁰⁸Pb*/²⁰⁶Pb than Kea trend lavas. Loa and Kea trend lavas form different trends in plots of ²⁰⁸Pb*/²⁰⁶Pb vs Sr-Nd-Hf-He isotopic ratios, and the Loihi component (high ³He/⁴He) is a common source component for Loa and Kea trend lavas. The Loa-Kea geochemical differences are inferred to reflect source differences; consequently, different models of plume structure have been proposed. However, I propose an alternative model in which Loa and Kea trend volcanoes sample a common geochemically heterogeneous source. / (cont.) The observed Loa-Kea geochemical differences is inferred as a result of temperature difference between Loa and Kea trend volcanoes which reflects their distances from the center of the hot plume core. / by Shichun Huang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 253-259. / by Wafik B. Beydoun. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 43-45). / In this thesis two separate projects are investigated, a stellar occultation by 2060 Chiron and rotationally resolved spectra of 1 Ceres. On 29 November 2011 UT, 2060 Chiron occulted a 14-mag star; data were successfully obtained at the 3-m IRTF on Mauna Kea and 2-m Faulkes North Telescope at Haleakala. The IRTF lightcurve shows a solid-body detection of Chiron's nucleus with a chord lasting 16.04 seconds, corresponding to a chord length of 158±14 km. Symmetric, dual extinction features in the Faulkes light curve indicate the presence of optically thick material roughly 300 km from the body midpoint. The duration of the features indicates a ~ 3 km feature separated by 10-14 km from a second - 7 km feature. The symmetry, optical thickness, and narrow size of these features allows for the intriguing possibility of a near-circular arc or shell of material. Rotationally resolved spectra of Ceres in the 0.43-0.85 micron range were observed using the DeVeny spectrograph on the Perkins 72-inch telescope at Lowell Observatory. Spectral differences as a function of phase were investigated. It is concluded that Ceres' surface is uniform at the 1% level at visible wavelengths. Additionally, the 0.6 and 0.67 pm features reported by Vilas and McFadden [1992] and Fornasier et al. [1999] are not seen at any phase at the 1% level. / by Jessica Dawn Ruprecht. / S.M.

Thesis: S.M. in Atmospheric Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / In title on title-page. double-underscored "x" appears as subscript. Cataloged from PDF version of thesis. / Includes bibliographical references (pages 42-49). / A 3-D chemical transport model with coupled oxidant-aerosol chemistry (GEOSChem) is used to analyze the influence of recent (2001 to 2010) growth in Asian NOx and Asian SO 2 emission on transpacific transport of Asian particulate matter, especially sulfate, by quantifying and analyzing the details of chemistry and its sequential influence on transpacific transport during spring and summer. From 2001 to 2010, the spring averaged Asian sulfate enhancement in the western US model surface layer increases by 0.01-0.03 [mu]g M-3 (about 4% of the surface sulfate concentration over the US at 2010 emission level). The net chemical production rate increases in the troposphere over Asia but decreases over the Pacific Ocean. The sulfate production pathway shifts toward gas phase production by OH (7-8% increase-China; 2-3% increase-Upper atmosphere Pacific Ocean) with corresponding reductions in aqueous phase production by H202 ; resulting in a switch of the most important production pathway from aqueous production by H202 to gas phase production by OH. Almost doubling the Asian NO. emission during the period has a negligible influence on Asian sulfate enhancement over the US; this change in Asian NOx emission causes the net chemical production rate to increase in the Asian boundary layer, but to decrease in the upper Asian atmosphere, and in the atmosphere over the Pacific Ocean and the US. This is because the Asian NOx emission growth strengthens the oxidizing power in the Asian boundary layer to more actively form sulfate (mostly removed by wet scavenging), reducing available SO2 for further production away from the source. The Asian NOx emission growth is the major driver in changing the sulfate production pathways toward the gas phase. The 20% increase in Asian SO 2 emission during the period is the primary driver in increasing Asian sulfate enhancement over the US; this change accelerates net sulfate production rate, and makes a minor contribution to shifting toward gas phase production by OH over the course of the transpacific transport. The calculated sulfate column burden shows a notable increase as a response to the changes in Asian emissions. However, the shifts in sulfate lifetime over China due to changes in Asian SO 2 and/or Asian NO, emission are almost negligible (generally 1-2%), and lifetimes over the upper level Pacific Ocean are generally reduced by 3-4%. / by Flora Min. / S.M. in Atmospheric Science

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (leaves 113-114). / by Cecelia DeLuca. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references. / This thesis explores the dependence of bedrock channel incision on coarse sediment supply through laboratory flume experiments and quantitative field observations of evolving channel morphology. Predictions of the saltation-abrasion model (Sklar and Dietrich, 2004) for sediment flux-dependent channel incision guide our efforts although the results are not model dependent. In channels where the dominant incision process is sediment abrasion, sediment transport and erosion are inherently coupled. Flume experiments support the form of sediment flux-dependent relations proposed in the saltation-abrasion model, but also suggest that the model is incomplete: channel bed morphology adjusts due to localized erosion, and bed morphology in turn influences local flow and sediment transport. The experiments document a positive feedback in which bedload is preferentially transported in local topographic lows due to lateral transport and abrasion in turn deepens those topographic lows. Under sediment-starved conditions this positive feedback results in the incision of narrow inner channels. In the Henry Mountains of southeast Utah, we monitored channel flow and resulting bedrock incision over 2.5 years in a human-perturbed bedrock channel where erosion had incised a narrow inner channel in which sediment transport and erosion were focused, similar to the flume experiments. In addition, the flow record shows that the maximum discharge flood was much less erosive than a lower but prolonged flood due to snowmelt flow. Large flash floods can be net depositors of coarse sediment in the channel, mantling the channel bed with coarse sediment and inhibiting erosion. / (cont.) Finally, a quantitative comparison of tributaries in a Henry Mountains river network shows that channels with higher coarse sediment loads maintain steeper channel slopes and are less incised than smaller drainage area tributaries with less coarse sediment but more exposed bedrock. These field observations validate the idea that sediment cover can inhibit channel incision into bedrock, and also suggest that the slope of incising bedrock channels can adjust to transport the sediment load of the channel rather than to incise bedrock. We found in the flume experiments that erosion adjusts the morphology of bedrock channels until a state is reached where channel flow just transports the imposed sediment load, suggesting that the equilibrium state of bedrock channels is a transport-limited condition. Together, the chapters demonstrate how incising channels respond to changes in coarse sediment load, emphasizing the effects of sediment cover in inhibiting incision and morphological adjustments of channel bed topography. / by Joel Peterson Johnson. / 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. 171-178). / Timing and system parameters were measured for seven transiting exoplanets: OGLETR- 56b (11 transits), OGLE-TR-132b (7), OGLE-TR-111b (6), OGLE-TR-113b (6), CoRoT-2b (3), OGLE-TR-10b (3), and XO-2b (2). Ground-based observations of 38 transits were made using three new frame-transfer instruments: POETS and MagICe2v on the 6.5m Magellan telescopes, and MORIS on the 3m IRTF. For each planet, all transit light curves including available literature data were jointly fit using a Monte Carlo Markov Chain method, providing accurate new values for the planetary radius and other parameters. Transit ephemerides have been updated and transit midtimes have been investigated for potential transit timing variations (TTVs) caused by other planets or moons. Our transit midtime analysis contradicts a claimed TTV for OGLE-TR-111b (Diaz et al., 2008), finding no evidence in data from 2005-2009. The radius, 1.019 + 0.026 Rj, is intermediate to previous values (Winn et al., 2007; Diaz et al., 2008). We confirm the radius of OGLE-TR-56b, which previously had only one light curve (Pont et al., 2007), as 1.332 ± 0.063 Rj, but find a longer duration by 15 minutes, while the orbital period, 1.2119094 ± 0.0000024, is unchanged. Times for OGLE-TR-10b are consistent with the ephemeris of Holman et al. (2007), though two literature transits show large deviations (586 ± 86 s; Pont et al., 2007) and (-612 ± 26 s; Bentley et al., 2009). Times for four planets (OGLE-TR-113b, OGLE-TR-132b, CoRoT-2b, and XO-2b), with midtime errors as small as 9 s, agree with published ephemerides and show no signs of TTVs. The orbital period of OGLE-TR-113b derived from new data from 2007-2009, however, is shorter by 0.24 ± 0.12 s compared to the period calculated for literature data from 2002 and 2005. If confirmed, this would be the first detection of a change in the orbital period of an exoplanet, which could be caused by orbital decay as the planet falls onto its star. / by Elisabeth Rose Adams. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Two maps in pocket following text. / Includes bibliographical references (p. 231-234). / by James David Robert Applegate. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / 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. 17-18). / We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u', g', and i' (358, 487, and 758 nm, respectively). The occultation probed latitudes 2°S and 1°N during immersion and emersion, respectively. A prominent central flash was present in only the i' filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i' profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396 ± 7 km and 401 ± 20 km (u' immersion and emersion); 354 ± 7 km and 387 ± 7 km (g' immersion and emersion); and 336 ± 5 km and 318 ± 4 km (i' immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3 ± 0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541-563]. / by Angela M. Zalucha. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references. / by Robert M. Sherrell. / Ph.D.