Atmospheric interactions affected both the mechanics of impact ejecta deposition and the environmental effects from the catastrophic Chicxulub impact at the Cretaceous-Paleogene (K-Pg) boundary. Hypervelocity reentry and subsequent sedimentation of Chicxulub impact spherules through the Earth's atmosphere was modeled using the KFIX-LPL two-phase flow code, which includes thermal radiation and operates at the necessary range of flow regimes and velocities. Spherules were injected into a model mesh approximating a two-dimensional slice of atmosphere at rates based on ballistic models of impact plume expansion. The spherules decelerate due to drag, compressing the upper atmosphere and reaching terminal velocity at ~70 km in altitude. A band of spherules accumulates at this altitude, below which is compressed cool air and above which is hot (>3000 K) relatively-empty atmosphere.Eventually the spherule-laden air becomes unstable and density currents form, transporting the spherules through the lower atmosphere collectively as plumes rather than individually at terminal velocity. This has implications for the depositional style and sedimentation rate of the global K-Pg boundary layer. Vertical density current formation in both incompressible (water) and compressible (air) fluids is evaluated numerically via KFIX-LPL simulations and analytically using new instability criteria. Models of density current formation due to particulate loading of water are compared to tephra fall experiments in order to validate the model instabilities.The impact spherules themselves obtain peak temperatures of 1300-1600 K and efficiently radiate that heat as thermal radiation. However, the downward thermal radiation emitted from decelerating spherules is increasingly blocked by previously-entered spherules settling lower in the atmosphere. This self-shielding effect strengthens with time as the settling spherule cloud thickens and becomes increasingly opaque, limiting both the magnitude and duration of the thermal pulse at the ground. For a nominal Chicxulub reentry model, the surface irradiance peaks at 6 kW/m <super>2 </super> and is above normal solar fluxes for ~25 minutes. Although biologic effects are still likely, self-shielding by spherules may have prevented the global wildfires previously postulated. However, submicron dust may act as a hot opaque cap in the upper atmosphere, potentially increasing the thermal pulse beyond the threshold for forest ignition.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17865号 / 工博第3774号 / 新制||工||1577(附属図書館) / 30685 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 牛島 省, 教授 角 哲也, 准教授 米山 望 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The Seattle District wants to better manage the Ballard Locks and structures along the Lake Washington Ship Canal (LWSC) in a way that will maintain the environmental sustainability and biodiversity in the area. Due to strict salt water intrusion regulations in the LWSC, the Seattle District is working on upgrading their management practices such that they will resolve two inter-related problems. First, to improve the fish passage conditions for migrating salmon; and second, to learn how to better manage the salt wedge that forms and intrudes upstream. Based on the hydrodynamic and water quality results that are produced by this research, the Engineer Research and Development Center (ERDC) Portland Office will use their Eulerian-Lagrangian-Agent-Model (ELAM) to analyze fish patterns, looking for the most beneficial management schemes that assist salmon in migrating upstream. This research implemented CFD engineering techniques to help better understand the effectiveness of the hydraulic structures in the area, as well as come up with management practices that both mitigate the salt water intrusion from Puget Sound, and improve the migrating passages for salmon.

Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...

Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...