Modeling Studies Related to Carbon Dioxide Phase Change on Mars
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 resea...
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| Format: | Thesis |
| Language: | English |
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California Institute of Technology
2009
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| Online Access: | https://dx.doi.org/10.7907/e2r4-ss65 https://resolver.caltech.edu/CaltechETD:etd-05082009-120748 |
| Summary: | 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. 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). 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. 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. 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. 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. |
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