Chris, Geoff and others: make sure the final printed version has apostrophes (they’re lost in my version) and that Rick’s equations print ok




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SwIM Proposal

Development of Mars Atmosphere Model

Crowley et al.

Chris, Geoff and others: make sure the final printed version has apostrophes (they’re lost in my version) and that Rick’s equations print OK.




Development of an SwRI Mars Atmosphere Model




Principal Investigator: Geoff Crowley (15)

Co-Investigators:

Christopher J. Freitas (18), Mark Bullock (15), Leslie Young (15), Walter Huebner (15), Dan Boice (15), Randy Gladstone (15), David Grinspoon (15), Richard Link (15).



External Unfunded Collaborators:



Steve Bougher (U.Arizona) - Mars upper atmosphere

Steven Clifford (LPI, Houston) - Mars hydrology, volatiles

James Brad Dalton (NASA-Ames) - Mars balloon missions




1. Introduction


The exploration of Mars is currently the centerpiece of NASA planetary research. This 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, we plan 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, the GCM code proposed here, may some day be used in support of missions that address answering this second question.

There are several key issues that 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 interest to NASA, from the scientific context, are understanding diurnal, seasonal and epoch water exchange and volatile loss throughout Martian history. 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 apparent lack of water on the planet. A complete GCM model including volatile loss processes will require explicit ground interaction, with varying composition such as upward fluxes of H2O that are required for a study of hydrogen (a photodissociation product of water) chemistry in the upper atmosphere. The volatile loss problem also requires a GCM model to include the thermosphere and ionosphere, in order to obtain better background information on the O/H corona around Mars. Including these regions in a Mars GCM allows for the estimation of 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.

There are several existing three-dimensional GCM codes, but they have tended to be focused on the description of different, discrete layers of the Mars atmosphere. These models are:

  1. NCAR/UArizona model – this model describes the Mars ionosphere and thermosphere, which extend from 70-300 km altitudes. It specifically excludes any dust interactions, which are assumed to be less important above 50 km. It has been used to predict aerobraking maneuvers for NASA’s Mars Global Surveyor and other missions (Bougher, private communication, December 2001).

  2. NASA/Ames model – this model extends from the ground to 120 km, and includes the effects of varying topography, albedo and convective adjustment. There is an effort underway at NCAR to couple the AMES and NCAR/UArizona models. In it current state, the coupled model passes information upward, but not downward. In addition, there are difficulties in the model coupling procedure due to the fact that the winds near 70 km, at the boundary between the models, are non-zero. Further, the crossover level from local thermodynamic equilibrium (LTE) to non-LTE occurs near 80 km, which has make the artificial boundary condition specification at the model’s interface to be difficult to formulate.

  3. French model - this model extends from the ground surface to 120 km and has similar capabilities to the NASA/Ames model.

  4. British model – this model appears to have lost favor and its development has languished.

As demonstrated above, no existing GCM model resolves the physics of the Martian atmosphere from the ground surface through the ionosphere in a single set of equations and boundary conditions. The NCAR/Ames coupled model attempts to resolve this region (ground surface through ionosphere), but may be limited in application due to the artificial boundary condition that must be applied at the interface between the models. We believe that there is a need for an alternative approach to the development of a Mars GCM. It is proposed here to begin the development of such a Mars GCM. One that is capable of directly modeling ground surface processes, escape flux processes at the top of the atmosphere, and all intervening processes that occur in the region bounded by these two extremes of ground plane and top of the atmosphere.

The new model proposed for development at SwRI will be based on the SwRI Advanced SPace ENvironment (ASPEN) model of the Earth’s middle and upper atmosphere. The ASPEN code was developed by Crowley and Freitas (2002) under IR projects (15-XXXXX and 15-XXXXX) and with external funding. This is a fully parallelized model running on the Div 18/15 Beowulf system. ASPEN solves the momentum and thermodynamic equations to predict temperature and wind fields from 10.0 mb to 0.01 mb pressure levels. On the Earth, these pressures correspond to an altitude range of 30 km to 500 km, CHECK THIS UPPER ALTITUDE -- RECTIFY WITH PRESSURE OF UPPER BOUNDARY while for Mars, these pressure levels would include the entire Martian atmosphere. The model includes major and minor composition modules, and solves for radiative transfer and a fully coupled ionosphere-thermosphere with electrodynamics.

Figure 1 displays the complete vision of the project team for the development of this new Mars GCM. As stated, this Mars GCM will be based on the ASPEN model of Earth's atmosphere, developed at SwRI by PI Crowley and Co-I Freitas (see Section 2.1), The Mars model will include ionospheric chemistry, using the Mars ionosphere model developed at SwRI by Co-I Rick Link (see Section 2.5); radiative transfer, including scattering by gases and aerosols, using code developed at SwRI by Co-Is Bullock and Grinspoon (see Section 2.3); transport of mass, energy, and momentum through the planetary boundary layer, including interaction with volatile surfaces, using models developed at SwRI by Co-Is Freitas, Boice, Heubner, and Young (see Section 2.2); hydrology, initially using models developed by external collaborator Clifford, but eventually incorporating models developed at SwRI in Division 20 (see Section 5); and the evolution of the Deuterium to Hydrogen (D/H) ratio, using models developed at SwRI by Co-I Grinspoon (see Section 2.4).



Figure 1. Scientific Vision (Mars's temperature as a function of altitude is shown in dark green for context).
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