Modeling Studies Related to Carbon Dioxide Phase Change on Mars

• Main Author: Guo, Xin (Vincent)
• Format: Others
• Published: 2009
• Online Access: https://thesis.library.caltech.edu/1683/1/thesis_1.0_2009_04_dbl.pdf; Guo, Xin (Vincent) (2009) Modeling Studies Related to Carbon Dioxide Phase Change on Mars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/E2R4-SS65. https://resolver.caltech.edu/CaltechETD:etd-05082009-120748 <https://resolver.caltech.edu/CaltechETD:etd-05082009-120748>

<p>Carbon dioxide (CO₂) is the most abundant gaseous species in the atmosphere of Mars. Phase change of CO₂, predominantly between gas and solid, is the most eminent feature in the current Martian atmosphere. Correct and thorough understanding of the CO₂ cycle on Mars is crucial to the scientific research of Mars, including (but not limited to) climatology, meteorology, paleo-climatology, geomorphology, geology, and astrobiology.</p> <p>This dissertation focuses on modeling the CO₂ phase change and coupling the process with a Mars General Circulation Model (GCM) ― the Mars Weather Forecast and Research (MarsWRF) model to study the climate of Mars. Two major forms of the CO₂ phase change are included: direct deposition/sublimation to/from the surface (exchange with surface frost) and atmospheric condensation/evaporation (exchange with "snow", which later will either precipitate to the ground and become a part of the surface reservoir, or evaporate before it reaches the surface).</p> <p>The first component has been historically simulated by a surface energy balance model. The energy balance calculations in MarsWRF, especially the physics module associated with subsurface heat conduction, are improved. The GCM is fine-tuned by changing the values of the seasonal ice cap albedos and emissivities and the total CO₂ mass in the system (later the heat conductivity of the polar soil). Resulted surface pressure cycle, which is a good indicator of the atmospheric reservoir of CO₂, matches the in situ measurements made by the Viking Landers extremely well. This fitting algorithm can be used for tuning of GCMs and for exploration of more complicated physical processes.</p> <p>The second component can be solved by a simple energy balance model in the atmosphere as well. However, it is widely accepted that sophisticated microphysics models may be required for more accurate simulations. A complete microphysics model, which calculates the nucleation process and ice particle growth process, is incorporated to MarsWRF. Preliminary simulation results show promising agreement with spacecraft observations.</p> <p>When an insolation-dependent frost albedo is included, MarsWRF is able to produce a perennial CO₂ cap near the south pole of Mars. This is the first time that any GCM has successfully predicted a residual cap. This mechanism is necessary for a simple energy balance model to reproduce the perennial ice cap, and may shed some light on the ages and the cycles of the perennial caps.</p> <p>A mass balance model is developed to simulate the non-condensable gas mass mixing ratio variation during the CO₂ phase change. When coupled with MarsWRF, the non-condensable gas cycle agrees qualitatively with the Gamma Ray Spectrometer data and other GCM results. It provides a benchmark check to the GCM itself and an independent way to study the dynamics of the Martian atmosphere.</p>