Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Lora, Juan

Abstract

Titan, the largest moon of Saturn, is the only world apart from Earth known to have a thick nitrogen dominated atmosphere which supports stable liquid on its surface. High in Titan's atmosphere, the destruction of nitrogen and methane (Titan's second most abundant molecule) initiates an intricate web of chemical reactions that produce a suite of large hydrocarbon and nitrile species, and ultimately lead to Titan's characteristic orange haze. The aerosols in Titan's atmosphere strongly absorb solar shortwave radiation, which leads to the development of a stratopause (akin to the development of Earth's stratopause by the absorption of solar ultraviolet light by stratospheric ozone) which separates the two layers of Titan's middle atmosphere: the stratosphere from about 40 to 300 km above the surface, and the mesosphere from about 300 to 600 km above the surface. This dissertation seeks to identify the driving mechanisms that control the seasonal-scale evolution of Titan's middle atmospheric dynamics and composition. Chapter 1 reviews the history of Titan observations and atmospheric modeling. Chapter 2 discusses the development of the Seasonally Varying Radiative Species (SVRS) dataset and the impacts of including the observed seasonal-scale composition changes on Titan's middle atmospheric circulation. Chapter 3 quantifies the seasonal-scale drivers of Titan's heat and momentum budgets by mean flow and transient eddies. Chapter 4 presents a new passive tracer advection scheme and quantifies the mechanisms that transport trace molecules through Titan's atmosphere. Chapter 5 shows the first measurement of hydrogen isocyanide in Titan's stratosphere and discusses the implications of this measurement on our understanding of Titan's nitrile chemistry. Chapter 6 outlines outstanding questions in Titan's middle atmospheric dynamics and chemistry, and shows putative results on the strength of coupling between Titan's circulation and radiatively active tracers.

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