Martian CO2, Water and Dust Cycles in GISS ROCKE-3D GCM: Latest Development

We present a Mars General Circulation Model (GCM) based on ROCKE-3D [1] (Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics) planetary GCM. ROCKE-3D was developed as a generalization of its parent Earth GCM, GISS ModelE2 [2], by coupling it to the SOCRATES [3,4] (Suite of Community Radiative Transfer codes based on Edwards and Slingo), an extremely flexible radiative transfer model, and by implementing a flexible algorithm for specifying the orbital parameters of the planet amongst other modifications. It inherited all standard Earth GCM functionality, such as a complete hydrological cycle (including ground hydrology) and the ability to model atmospheric tracers (including dust). It is also able to condense the major atmospheric component (CO2 in Mars' case) at the surface, though CO2 clouds have not yet been implemented. Recent development included the implementation of radiatively active dust, separate treatment of CO2 and H2O snow and ground hydrology tuning for conditions below the triple point of water.

In our experiments the model uses a 4ox5o horizontal resolution and 40 layers vertically, with the upper boundary at ~0.7 microbar. We use MOLA and TES observations for the topography and the ground albedo respectively. The ground is dry (initially) sand, but to account for the presence of H2O ice in the Northern polar cap we initialize the model with a H2O snow layer to the north of 80o N (4 m thick water equivalent layer). We investigate the ability of our model to reproduce the seasonal cycle of observed quantities such as the atmospheric temperature, the surface pressure, the atmospheric water, and the optical depth of the dust. We compare the results of our simulations to observations provided by the Mars Climate Sounder for the atmospheric temperature and the dust optical depth, SPICAM on Mars Express for the atmospheric water, and Viking 2 measurements for the surface pressure. We find that with proper tuning of snow albedo, hydrological properties of the surface and the efficiency of dust emission we get a good agreement with the observations.

References: [1]Way M. J. et al. (2017) ApJS, 231, 12. [2] Kelley, M. et al. (2020) J. Adv. Model. Earth Syst., 12, no. 8, e2019MS002025. [3] Edwards, J. M. (1996), JAtS, 53, 1921. [4] Edwards, J. M., & Slingo, A. (1996), QJRMS, 122, 689.