Ph.D. Dissertation Defense

Diurnal and Seasonal Variability of Uranus’ Magnetosphere under Different IMF

The magnetosphere of Uranus is far from well known since there was only one fly-by measurement in history. In order to study the magnetosphere and its coupling mechanism with the solar wind, we used our multifluid magnetohydrodynamics (MHD) model [Cao and Paty, 2017] to successfully simulate the variation of the global magnetosphere of Uranus and have predicted potential favorable reconnection locations.

Examining the spatiotemporal variability and direct radiative impacts of mineral dust in Central Asia using a coupled regional modeling system and satellite-based sensors

The airborne dust has been well recognized to have a significant impact on the climate system at varying spatial scales (through direct, indirect, and semi-direct effects), on biochemistry (providing marine phytoplankton with iron nutrient), and on human health (causing severe disease) during the past decades. However, current estimations of these effects are still very uncertain because the dust cycle involves many complex physical and chemical processes in the atmosphere at different spatial and temporal scales, as well as the state of surfaces prone to the dust emission.

Callisto: Signatures of Plasma Interaction, Induction, and Energetic Particle Dynamics at the Galilean Moon

We present results from a three‐dimensional simulation model of the complex plasma environment near the Jovian moon Callisto. Beneath Callisto’s icy crust possibly lies a liquid saltwater ocean, properties of which can be constrained through magnetic induction signatures generated by Jupiter’s time‐varying magnetospheric field.

Role of Thiols in Microbial Metal Reduction and Importance of Organic-Fe(III) Complexes on the Benthic Flux of Iron from Continental Margin Sediments

Iron and manganese transformation reactions greatly impact a variety of environmental and biogeochemical processes in the environment, including the transport and degradation of inorganic and organic contaminants, the cycling of organic carbon, and the transformation a variety of other biogeochemically important chemical species. In addition, as essential nutrient, iron exerts a substantial control on ocean productivity and export of organic matter to the deep ocean.

The impacts of atmospheric radiation on studies of planetary habitability

The conditions required for Earth-like life to emerge on a planetary body are thought to include the presence of liquid water, the availability of energy and the existence of organic material. There are situations when determining whether the above conditions exist on a planetary body is not possible without a detailed understanding of the radiative processes occurring in a planet's atmosphere. In this work, studies of the radiative flux and transfer within planetary atmospheres are carried out in order to elucidate whether certain planetary bodies may be habitable.

Understanding earthquake triggering and fault slip behavior based on complete earthquake catalogs

Large mainshocks can alter stress field on subsurface asperities across broad spatial and temporal windows, which would promote or inhibit fault motion. Beyond rapid rupture during earthquakes, fault can also slip at a steady rate without seismic radiation. In between these two end members, slow slip events have been documented within the conditionally stable transition zone.

Wildfires in Earth System: The Driver, Transport, and Feedback

Wildfires release large amounts of greenhouse gases, carbonaceous aerosols, and other pollutants, therefore having complex impacts on the earth climate, local weather, and air quality. To study the transport of the wildfire emissions, a plume height dataset has been developed. The resulting dataset from 2002 to 2010 captured well the observed MISR plume height distribution. By adding the plume height dataset in the climate model, the plume-rise enhanced AOD downstream of the wildfire spots by 20 to 50%.

Effects of metal impurity on the structure and reactivity of manganese oxides

Mn oxides are among the most ubiquitous and reactive mineral phases in natural environments and significantly influence the cycles of essential elements such as C and N, as well as the transport and fate of a wide range of metals. The structure and reactivity of Mn oxides were extensively studied but most of these studies used pure Mn oxide minerals, which are barely found in real geological or engineering settings.

Geochemical controls of the microbially mediated redox cycling of uranium and iron

Mining and processing of uranium ore, followed by improper disposal and aging nuclear waste infrastructure, have left behind a legacy of uranium contamination across the United States. Uranium bioreduction, an in situ bioremediation strategy which promotes microbial reduction of aqueous U(VI) to insoluble U(IV) solids, has proven successful at decreasing groundwater uranium concentrations below regulatory limits. However, iron 

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