Development of an SwRI Mars Atmosphere Model, 15-9312

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Principal Investigator
Geoffrey Crowley
Christopher Freitas
Mark Bullock
D. Boice
Leslie Young
C. Hackert
S. Chocron
G. Wene, UTSA
M. Westerhoff, UTSA
David Grinspoon
R. Link
W. Huebner

Inclusive Dates: 05/1/02 - Current

Background - The exploration of Mars is currently the centerpiece of NASA planetary research. This importance has been driven in recent times by the possibility that this planet was once more Earth-like than it is today. This possibility raises questions as to what processes and forces have modified the Martian environment and created the planet we observe today. In addition, the possibility of biological life on Mars, at sometime in its history, based on fossil records in meteorites has also spurred plans for significant planetary missions to Mars and the funding of supporting scientific research. The early exploration phase of Mars is somewhat complete, and over the short term (of a few years), a focus will be on the detailed interpretation of existing data and its use in the performance of modeling activities to support scientific understanding. These activities will be necessary and essential to support the design of future missions to Mars.

There are two primary questions that scientists wish to answer in the context of Mars. First, what processes and forces shaped the development of the present-day atmosphere and resulted in the presumed loss of water? And, second, did biological life develop on Mars? In this proposed effort, the team plans on initiating the development of a computational tool, a General Circulation Model (GCM), which will support research designed to answer the first question. The second question is presently outside the scope of this effort. However, it is likely that the answer to the second question will depend on the history of water on Mars. Several key issues are not addressed by existing models of the Martian atmosphere, and thus modeling of the Mars atmosphere remains a rich subject for investigation and funding. Of major scientific interest to NASA is the understanding of diurnal, seasonal, and epochal water transport and volatile loss. Volatile loss is a cornerstone of a number of important science questions because it must be understood to help explain the current atmospheric state and the relative lack of water on the planet. A complete GCM model that considers volatile loss processes must include explicit ground interaction with the lower atmosphere, vertical transport of H2O, and enough chemistry to reasonably represent the loss of H and H2 (and heavier species) from the upper atmosphere and exosphere. Including these regions in a Mars GCM allows for the estimation of global escape fluxes for the present time, which can then be extrapolated backward in time to post-cast the atmospheric state at significantly earlier time periods with different orbital elements.

Approach - The new Mars GCM will extend from the planetary surface to altitudes of approximately 500 kilometers, thus explicitly coupling the lower and upper atmospheres of Mars and overcoming deficiencies of existing models. It will include interactions between the ground and the atmosphere: specifically gas phase and dust particle exchange between the two regions and the effect of topography. The Planetary Boundary Layer (PBL) is essential to the dynamics of the lower atmosphere of any solid body with a sufficiently dense atmospheric mixture. It is at the ground surface where the fluid atmosphere interfaces to important sources and repositories of energy (thermal and viscous) and mass (chemical species and particles). The model will thus predict volatile loss, including the effect of ground interaction. The volatile transport will be simulated over both short (daily) and geological timescales to study the water distribution and to predict the D/H ratio of the present day atmosphere, thereby helping to constrain the history of water on the planet. The Mars ionosphere will be simulated with better chemistry than previous models. An embedded ionospheric module will provide improved ionospheric specifications needed to accurately simulate the D/H response.

Conceptually the project devolves into the following areas.

a) Basics (radius, rotation rate, gravity) d) Radiative Transport
b) Ground-atmosphere interaction  e) D/H Ratio
c) Boundary layer/dust transportation  f) Ionosphere

The new model proposed for development at SwRI will solve the momentum and thermodynamic equations to predict temperature and wind fields from the surface (~6-mb pressure) to 10-10 mb pressure levels, which would include the entire Martian atmosphere. The model will use a sigma-coordinate system to account for topography. The model includes composition and chemistry modules, and solves for radiative transfer and a coupled ionosphere. One key aspect to modeling the Mars atmosphere is the inclusion of PBL processes, and the lifting of dust into the atmosphere. The model will be fully parallelized running on the SwRI Beowulf system.

Accomplishments - The model development is underway, and the team has generated a preliminary model of the Mars atmosphere down to the peak of Olympus Mons, including radiative effects and chemistry. The next step is to extend the model to the ground, and include the surface boundary conditions.

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