Ph.D. Dissertation Defense

Understanding ocean iron dynamics and impacts on marine ecosystems

 Iron (Fe) is one of most the important nutrients for phytoplankton growth in the ocean, making it a crucial element in the regulation of the ocean carbon balance and biogeochemical cycles. Atmospheric deposition of Fe to the ocean has been increased due to human activities, which can significantly alter the marine ecosystem. These necessitate a comprehensive understanding of how the ocean Fe cycling operates and how it will respond to human perturbations.

Dynamics, Variability, and Model Representations of U.S. Hydrological Extremes

Hydrological extremes, including both extreme precipitation events and droughts, have profound impacts on human life, health, and socioeconomic well-being. U.S. hydrological extremes are dynamically connected to large-scale meteorological patterns (LMPs) (e.g., atmospheric blocking events, cutoff-low systems, and cyclones/anticyclones) and planetary-scale climate modes (PCMs) (e.g., El Niño Southern Oscillation and Pacific Decadal Oscillation).

Atlantic Meridional Overturning Circulation Variability Since the Last Glaciation: Insights from a Novel Multiproxy Approach

The Atlantic Meridional Overturning Circulation (AMOC) transports warm surface water northward across the equator, carrying heat from the Southern to the Northern Hemisphere. AMOC plays a central role in the global redistribution of heat and precipitation during both abrupt and longerterm climate shifts. Over the next century, AMOC is projected to weaken due to greenhouse gas warming, though the skill of these projections is dependent on a better understanding of how AMOC changes are forced, including the evolving states of its constituent water masses.

Multiphase Reactive Transport in Planetary Ices

The goal of this work has been to create a comprehensive picture of planetary ice shells given the fact that ocean derived ices behave as multiphase reactive porous media. Furthermore, it seeks to assess the implications this has on the geophysics and habitability of ice-ocean worlds such that testable predictions can be made that relate observable features to interior properties and processes.

Anthropogenic and Natural NOx Emissions over the United States: Comprehensive Evaluations and Implications for Surface Ozone Prediction

Nitrogen oxides (NOx = NO + NO2) play crucial roles in the formation of ozone, aerosol, and acid rain which are unfavorable to human health, climate, and ecosystem stabilities. NOx is emitted by both anthropogenic and natural sources, such as fossil fuel combustion, soil bacteria, lightning, etc. Accurate knowledge of NOx emissions is essential for relevant scientific research and air pollution control policies.

Postseismic Response Following the 2012 Mw 7.6 Nicoya, Costa Rica Earthquake

Characterization of the surface deformation related to the 2012
moment magnitude (Mw) 7.6 Nicoya earthquake was undertaken using
continuous and campaign Global Positioning System (GPS) observations. This
location is uniquely situated to monitor megathrust conditions as the peninsula
extends to within 60 km of the trench. The entirety of the postseismic and
relocking period were considered, totaling 5 years. Seismic observations were
also included, to cumulatively elucidate the timing and spatial extent of

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.

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