Browsing by Subject "Plume"
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Item Investigation of the upper mantle beneath the Hawaiian Island chain using PP-precursors(2013-08) Rogers, Kenneth D.; Gurrola, Harold; Nagihara, Seiichi; Karlsson, Haraldur R.The Hawaiian hotspot is of great geological significance, but data collection in the area can be challenging due to the water depth around these islands. By using PP bounce point data, with receivers in mainland United States, we analyze the area with a greater wealth of data than possible using data collected locally. The increased amount of data, in addition to new beamforming and iterative deconvolution techniques, has increased the frequency content in PP precursor data, from around the traditional 0.01 Hz to above 5 Hz, enabling us to image to shallower depths and thinner layers than previously possible. Profiles of stacked PP precursors across the island chain were produced along perpendicular lines. Data were stacked in bins 1˚ along the profiles and 4˚ perpendicular to the profile (parallel to the island chain). An additional profile was produced some 10˚ away from the island chain as a control group. The control group shows pairs of high- and low-velocity horizons in the mantle. These may be the base and top of shear zones. These horizons are strongly disrupted near the Hawaiian Island chain. In the lithosphere, low velocity zones are more abundant to the south of the island chain but are less common on the north side. If these indicate melt, the low velocity zones may be blocked by the Islands, which are sinking into the lithosphere. As this study and other recent work imply the hot spot is more active to the southwest of the island chain than to the north, the island chain itself may be causing the crust to warp downward into the mantle and could act as a dam to melt migrating to the north. Furthermore, we believe that the island’s weight downwarping the lithosphere causes a crack to propagate out past the youngest island, which also acts as a dam that keeps most of the melt to the southwest of the island chain.Item Parametric study of LCROSS impact plume(2013-12) Lamb, Justin Meredith; Goldstein, David Benjamin, doctor of aeronauticsIn 2009, NASA's LCROSS mission impacted Cabeus Crater near the Lunar South Pole with the spent Centaur upper stage rocket. The impact was observed by the trailing sheperding spacecraft (S-S/C) that impacted the moon 250 seconds after the Centaur impact. The main objective of the LCROSS mission was to verify the existence of water ice in the lunar regolith---the subsequent analysis of the data confirmed water ice present in the crater. The analysis of the S-S/C instrument data suggested that the plume consisted of two components: a central "spike" component and a thin, outward "cone" component. A model has been developed at The University of Texas at Austin improve the analysis of the data obtained by the S-S/C. This model is created with a free-molecular ballistic grain code that involves simulating individual regolith grains in the debris plume through grain-heating and grain-movement models and then modeling the spectral radiance properties of the grains as observed by the S-S/C. Mie scattering theory is used to model scattering and absorption of incoming solar radiation by the particles in the plume assuming they are perfect spheres. The UT LCROSS code was utilized in a parametric study that evaluated the effect of variations in assumed model plume parameters on the modeling of S-S/C UV-VIS instrument observations. The plume parameters were chosen based on the assumption that the dust plume was split into two components: a central spike and a surrounding high angle cone. The following parameters were varied: the spike and cone angles, the spike and cone grain radius distributions, and the spike mass fraction. The following parameters could be varied but were given fixed values: ice fraction between plume components, ice grain purity, albedo, and ice fraction in plume. The impact of these plume parameters upon plume brightness and blue/red color ratio was determined. Two grain models were used. In the initial grain species model all grains have a soil core surrounded by a thin ice shell. In the second, two species model two grain types were utilized: a pure ice grain component and a pure soil grain component.Item Simulating water vapor plumes on Europa(2015-12) Berg, Jared James; Goldstein, David Benjamin, doctor of aeronautics; Varghese, PhilipA computational investigation of water vapor plumes on the Jovian moon Europa was performed with a focus on characteristics relevant to observation and spacecraft mission operations. The Direct Simulation Monte Carlo (DSMC) method was implemented to model the plume expansion. The structure of the plume, including the number density, temperature, and velocity fields was determined. Integrated line of sight column densities of ~1018 H2O molecules/m2 were calculated and compared to observations. The possibility of grain condensation above the vent was considered, but determined to be negligible for the postulated vent size. However, preexisting grains of three diameters (0.1, 1, 50 μm) were included in the simulation and their trajectories examined. A preliminary study of photodissociation of H2O into OH was performed to demonstrate the behavior of daughter species. Different vent parameters were evaluated to determine their effects on the plume, including vent Mach number (Mach 2, 3, 5) and a reduced temperature “Cold” case that was a proxy for energy loss to the region surrounding the vent. Future research pathways are discussed, including higher mass flow cases, unsteady plumes, and accurate modeling of internal energy modes in photodissociation products.