Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (p. 185-195). / Midlevel ventilation, or the flux of low-entropy air into the inner core of a tropical cyclone (TC), is a hypothesized mechanism by which environmental vertical wind shear can constrain a TC's intensity. An idealized framework is developed to assess how ventilation affects TC intensity via two pathways: downdrafts outside the eyewall and eddy fluxes directly into the eyewall. Three key aspects are found: ventilation has a detrimental effect on TC intensity by decreasing the maximum steady state intensity, imposing a minimum intensity below which a TC will unconditionally decay, and providing an upper ventilation bound beyond which no steady TC can exist. Based on the idealized framework, a ventilation index is derived that is equal to the environmental vertical wind shear times the midlevel entropy deficit divided by the potential intensity. The ventilation index has a strong influence on the present-day climatology of tropical cyclogenesis and the distribution of TC intensification. Additionally, changes in the ventilation index are also examined in general circulation models (GCMs) between the late 20th century and the late 22nd century. Individual GCMs indicate potential regional shifts in preferred locations of tropical cyclogenesis and changes in TC intensity statistics due to shifts in the seasonal ventilation index, but a statistically significant projection cannot be given. The GCMs do show a robust increase in the midlevel entropy deficit and potential intensity nearly everywhere in the tropics. Lastly, an axisymmetric model with parameterized ventilation is used to examine the sensitivity of TC intensity to the strength and location of the ventilation and to examine the findings of the idealized framework. Increasing the strength of the ventilation and placing the ventilation at lower to middle levels results in a greater decrease in the quasi-steady intensity, whereas upper-level ventilation has little effect on the intensity. For strong ventilation, an oscillatory intensity regime materializes and is tied to transient convective bursts and strong downdrafts into the boundary layer. The sensitivity of TC intensity to ventilation can be viewed in the context of a modified thermal wind relation or the fractional Carnot efficiency of the inner-core. / by Brian Hong-An Tang. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 45-47). / Nitrous oxide (N2O) is a powerful greenhouse gas and ozone depleting substance, but its natural sources remain poorly constrained. Marine emissions are likely much higher than IPCC estimates predict, due to unusually high emissions from the oxygen minimum zones (OMZs) in the eastern tropical Pacific and Arabian Sea that are not accounted for in assessments. Measurements of atmospheric concentrations from a selection of AGAGE stations around the Pacific Ocean were combined with back-trajectories calculated using the HYSPLIT4 atmospheric model, in order to study the relative importance of OMZs on Pacific N2O emissions. Spatial and temporal variability in nitrous oxide concentrations were analyzed in order to determine potential regions of higher emissions, as well as the impacts of ENSO on biogeochemistry in the OMZs. Air parcels that passed over the oxygen minimum zone in the Eastern Tropical South Pacific were found to have N2O concentrations as much as 0.5 ppb higher than average. Average concentrations over the OMZ were modulated by an additional ~0.2 ppb higher during La Niia events and ~0.2 ppb lower during El Niio periods, a deviation of the same order of magnitude as N2O's seasonal cycle. Comparisons with CFC-12 and SF6 suggested strong influences on nitrous oxide concentrations in the Southern Hemisphere from stratosphere-troposphere exchange, but little influence from inter-hemispheric transport. / by Elisabeth L. Boles. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (p. 74-80). / by Mousumi Roy. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (leaves 302-311). / by David Anton Dinter. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995. / Includes bibliographical references (leaf 15). / by Janice A. Vatland. / B.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 78-79. / by Robert Paul d'Entremont. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references (p. 49-50). / Laboratory flume experiments are used to examine the role of suspended sediment abrasion in bedrock channel erosion. A range of topographies was used, from a planar bed to a sinuous and scalloped inner channel. Experiments were run separately with bedload (used to form topography) and suspended load at a variety of water flows and sediment fluxes. Sediment samples were collected to determine mass flux and concentration profiles. Erosion was measured between each timestep and erosion rate determined for a variety of conditions. Rouse, Froude, and Stokes numbers were calculated from measured data for various timesteps to determine mode of sediment transport and flow characteristics. Flow was supercritical, and sediment was in suspension. Erosion patterns around imposed topography perturbations (a rock protrusion and a drilled pothole) were briefly examined. A hydraulic jump was used in one timestep to see the effect of the transition from supercritical to subcritical flow. Suspended sediment causes erosion in all bed morphologies. The amount and pattern of erosion are coupled to topography, but are not constrained by it to the same degree as bedload. As in the case of bedload, suspended sediment erosion is strongly coupled to sediment flux. / by Katrina Muir Cornell. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmosphere and Planetary Sciences, 1988. / Includes bibliographical references. / by M. Ross Vennell. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. / Includes bibliographical references (p. 108-120). / By virtue of their landing on Earth, meteorites reside in near-Earth object (NEO) orbits prior to their arrival. Thus the population of observable NEOs, in principle, give the best representation of meteorite source bodies. By linking meteorites to NEOs, and linking NOEs to their most likely main-belt source locations, we seek to gain insight into the original solar system formation locations for different meteorite classes. To forge the first link between meteorites and NEOs, we have developed a three dimensional method for quantitative comparisons between laboratory measurements of meteorites and telescopic measurements of near-Earth objects. We utilize meteorite spectra from the Reflectance Experiment Laboratory (RELAB) database and the NEO data from the SpeX instrument on the NASA Infrared Facility (IRTF). Using the Modified Gaussian Model (MGM) as a mathematical tool, we treat asteroid and meteorite spectra identically in the calculation of 1-micron and 2-micron geometric band centers and their band area ratios (BARs). Using these identical numerical parameters we quantitatively compare the spectral properties of S-, Sq-, Q- and V-type NEOs with the spectral properties of the meteorites in the H, L, LL and HED meteorite classes. For each NEO spectrum, we assign a set of probabilities for it being related to each of these meteorite classes. Our NEO-meteorite correlation probabilities are then convolved with NEO source region probabilities to yield a final set of meteorite-source region correlations. An apparent (significant at the 2.1-sigma level) source region signature is found for the H chondrites to be preferentially delivered to the inner solar system through the 3:1 mean motion resonance. A 3:1 resonance H chondrite source region is consistent with the short cosmic ray exposure ages known for H chondrites. The spectroscopy of asteroids is subject to several sources of inherent error. The source region model used a variety of S-type spectra without attempting to infer mineralogy. Yet work by Gaffey et al. (1993) describes the S-asteroid class as home to a wide variety of mineralogies. Using data from the Small Main-belt Asteroid Spectroscopic Survey (SMASS), the 24-color asteroid survey and the 52-color asteroid survey, the spectral parameters of subclass members are investigated to predict possible errors to our model. While spectra are a diagnostic tool, there are factors inherent to the environment of near-Earth asteroids that pose ambiguities, such as grain size, temperature and space weathering.These factors are difficult to deconvolve from the compositional signal and are addressed here by simulated effects on meteorites from RELAB, Moroz et al. (2000) and Strazzulla et al (2005). A long-standing puzzle in asteroid science is the space weathering process and its implications for the relationship between S-type asteroids and ordinary chondrites. While Q-type asteroids are most spectrally similar to ordinary chondrites, these meteorites share certain diagnostic similarities with S-type asteroids. / (cont.) Binzel et al. (2004) statistically demonstrated a trend in spectral slope in near-Earth objects from 0.1 to 5 km. This analysis provided a missing link between the Q- and S-type by showing a reddening of spectral slope with larger diameter that corresponds to a transition from Q-type asteroid spectra to S-type asteroid spectra. This reddening of spectral slope is attributed to the effects of space weathering on the observable surface composition. This work shows preliminary results of a photometric survey of small Koronis family members. Observations of these objects were obtained in visible and near-infrared Harris and Sloan filters. Due to their common origin, Koronis family members have shown similar S-type spectroscopic signatures. We assume this consistency applies to the small-unclassified bodies. This provides a unique opportunity to compare the effects of the space weathering process on potentially ordinary chondrite-like bodies within a population of identical initial conditions. By examining a size range similar to the Binzel et al. work we hope to compare the slope reddening transition sizes within the near-Earth population and the main-belt. This data set should prove crucial to our understanding of the space weathering process and its relevant timescales. / by Cristina Ana Thomas. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Includes bibliographies. / by Robert L. Nowack. / Ph.D.