Dissertation/Thesis Abstract

Chemical Transport in the Atmospheres of Brown Dwarfs and Gas Giant Planets
by Bordwell, J. H., Ph.D., University of Colorado at Boulder, 2020, 166; 27735481
Abstract (Summary)

In the past thirty years, a wealth of new non-stellar objects similar in size to Jupiter has been found. These discoveries have opened up the field for a new kind of study of the atmospheric dynamics of brown dwarfs and gas giants, that exploits the spread in atmospheric conditions hosted by this large population. To connect the results of our simulations and models to observations, it is necessary to understand the interplay between chemistry and dynamical transport which imprints itself upon the observed global spectra from theses objects. In this thesis, we study local models of simplified atmospheric dynamics using the Dedalus pseudospectral simulation code, and explore the effects of these dynamics upon chemical transport using abstract chemical reactions. As part of this work, we derive numerically-motivated, improved parameterizations for the inclusion of chemical transport in chemical kinetics models where possible, and we evaluate the accuracy of the eddy diffusion approximation for different dynamical modes of transport.

We find through work in three separate projects that the most common method of including atmospheric transport in chemical models is not justified. In the case of convective dynamics, as detailed in Chapter 4, we find that the eddy diffusion approximation itself may be valid, but it is necessary to work with eddy diffusion coefficients that are a function of both height and the chemical reaction that is expected to quench. After an update to our background atmosphere model to enable work in coupled radiative-convective atmospheres, we have shown that when the radiative-convective boundary is deep within the atmosphere, waves that are convectively-generated may be damped, while waves that do not see this damping do not act diffusively based on chemical transport experiments (Chapters 5 and 6). Further work on elucidating the modes of gravity wave generation, in order to derive parameterizations that can be used to extend exploration of transport in larger stable regions, has shown that the problem is complex in a compressible atmosphere (Chapter 5).

Indexing (document details)
Advisor: Brown, Benjamin P
Commitee: Oishi, Jeffrey S, Rast, Mark P, Berta-Thompson, Zachory, Grooms, Ian
School: University of Colorado at Boulder
Department: Astrophysical and Planetary Sciences
School Location: United States -- Colorado
Source: DAI 81/11(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Astrophysics, Atmospheric sciences, Fluid mechanics
Keywords: Atmospheres, Brown dwarf, Disequilibrium chemistry, Exoplanet, Hot Jupiter, Jupiter
Publication Number: 27735481
ISBN: 9798645453121
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