The entire atmosphere of Mars is modeled from the surface to 300 km. The integrated approach establishes the coupled energetics, dynamics, and chemistry of the atmosphere from the ground to the exosphere. Quantification of the physical processes that couple the lower Martian atmosphere to the upper Martian atmosphere permits quantification of the impact of seasonal and solar-cycle variations of atmospheric dust-loading on the identified coupling processes, and consequently an examination of the of dust storm evolution and impact throughout the Martian atmosphere. The "Whole Atmosphere Climate Model" (WACM) general circulation code currently in use for modeling of the Earth atmosphere is adapted to the upper Martian atmosphere, and is joined to a new finite difference dynamical core originally designed for fine-mesh gridding in the earth's lower atmosphere. That lower atmosphere methodology is adapted to permit a terrain-following vertical coordinate system to accommodate the significant variations of Martian topology. Model verification and tuning is provided by Mars Global Surveyor and Mars Odyssey neutral and ion atmospheric density profiles, altitude profiles of neutral temperature, and inferred winds - so that a predictive capability of future Martian conditions is established. The adaptation of circulation models developed for the Earth atmosphere to the Martian atmosphere permits a new examination and evaluation test bed for improved physics-based model development on both planets.
The detailed characterization of the structure and dynamics of the Mars lower (0-80 km) and upper (~80-300 km) atmospheres is important for future Mars aerobraking, aerocapture, descent, and landed activities, and to understand the fundamental processes that maintain and drive variations in the present Mars climate. Strong coupling processes linking the Mars lower and upper atmospheres are crucial to quantify in order to predict upper atmosphere densities, temperatures, winds, and waves in preparation for these spacecraft operations. It is recognized that the entire Mars atmosphere is an integrated system that must be treated as a whole from the ground to the exobase. Modeling efforts must be tailored to address this integrated Mars system in order to reliably simulate the state and variations of the Mars lower and upper atmospheres over various timescales (e.g. solar cycle, inter-annual, seasonal, diurnal). The primary goal of this NSF research has been to develop and validate a Mars Whole Atmosphere Climate Model (MWACM) that extends from the ground to the exosphere of Mars. This University of Michigan effort combines the existing terrestrial Global Ionosphere-Thermosphere Model (GITM) framework [e.g. Ridley et al., 2006] with Mars fundamental physical parameters, ion-neutral chemistry, and key radiative processes in order to capture the basic observed features of the thermal, compositional, and dynamical structure of the Mars atmosphere from the ground to ~250 km. The MWACM three-dimensional code presently simulates the following neutral and plasma fields around the planet. Neutral temperatures are solved for self-consistently, but ion and electron temperatures are presently prescribed based upon Viking measurements. Key neutral species include: CO2, CO, O, N2, O2, and Ar. Key ion species (above ~80 km) include: O+, O2+, CO2+, N2+ and NO+. Three component neutral winds are calculated globally. Plasma velocities (zonal and meridional ion velocities) are not calculated, but await the coupling with a solar wind interaction (plasma) code. The MWACM code can be run for various horizontal and vertical resolutions. Typically, production runs are conducted for a 5x5 degree regular horizontal grid, with a constant 2.5 km vertical resolution (~0.25 scale height) above the lowest ~80 km. A "stretched" vertical grid is used at lower altitudes to accommodate the variable Mars terrain. The MWACM code can be run for various seasonal and solar cycle conditions (i.e periodic forcing), as well as solar flare and dust events (i.e. transient forcing). For example, Figure 1 shows model outputs for extreme solar cycle plus seasonal conditions for the Mars upper atmosphere. Neutral exosphere temperatures are illustrated near ~200 km (latitude versus local time). The noontime dayside temperature variation calculated is ~160 K (from ~180 to 340 K). This is similar to that observed from various Mars spacecraft measurements and recently calculated by other Mars upper atmosphere models [e.g. Bougher et al., 2009]. This temperature variation, and the underlying neutral and ion density structure, is important to quantify because it regulates the upper atmospheric reservoir available for neutral and ion escape from the planet. Such atmospheric loss may be partially responsible for atmospheric climate change on Mars. This MWACM code has also been used to investigate thermosphere-ionosphere responses to transient forcing events (i.e. dust storms and solar flares). For example, Figure 2 shows MWACM ionosphere responses to the April 15, 2001 solar flare also observed on Earth. These MWACM electron density results compare favorably with Mars Global Surveyor measurements made corresponding to the same solar flare event [Mendillo et al., 2006]. The electron densities (Figure 2) are modified significantly, much more so than on Earth. In short, these project simulations are very promising, and demonstrate that the MWACM code can be used for both steady-state and time-variable forcing to investigate observed (or to predict) thermosphere-ionosphere global features. The MWACM code is scheduled for numerical integration with the Michigan MHD (magneto-hydrodynamic: plasma) and the DSMC (Direct Simulation Monte Carlo: exosphere) codes for the self-consistent simulation of the Mars thermosphere-ionosphere-exosphere regions and the solar wind interaction with the planet. Detailed numerical integration will enable these three independent models to exchange fields with one another. The ultimate goal is to address volatile escape processes and the self-consistent neutral and ion loss rates from Mars for comparison with anticipated MAVEN spacecraft mission datasets (2014-2016).
