PEM (Planetary Evolution Model)

Overview of the PEM (Planetary Evolution Model)

The objective of the “Planetary Evolution Model” is to develop numerical climate models to simulate the past environments of Mars, explain the observed landforms, and, on this basis, better understand the past environment on Mars and its evolution.

PEM schematic view ; credit: Francois Forget

To accurately simulate the climate and the fate of volatiles for thousands to millions of years we must couple physical processes with very different timescale, ranging from clouds microphysics and atmospheric dynamics (represented in the GCM) to the evolution of lakes, glacier accumulation, and subsurface ice evolution.

Given the diversity and the complexity of the Martian paleoclimates, I choose to use use an ambitious “asynchronous coupling” between the slow ice and water reservoirs models and the GCM. In practice our innovative Mars evolution model will use a horizontal grid identical to that of the GCM, and include the same representation of the microclimate on slopes. In our case, we will run the Mars Evolution Model with a timestep of 50 to ~5000 years, depending upon the dynamics of the modeled system (smaller timesteps must first be used so that the different volatile reservoirs reach a quasi-equilibrium, then the timestep will depends on the evolution of the forcing, which is slow in the case of obliquity, for instance) . At each timestep, the inputs from the atmosphere (e.g. mean precipitation, sublimation and evaporation, temperatures, dust deposition) will be obtained through a multi-annual run of the Global Climate model using the outcome of the Mars Evolution Model as initial state.

PEM inputs and outputs

• start_evol.nc A Dynamical GCM start file
• startfi_evol.nc A physic GCM start file
• startfi_PEM.nc A start file specific to the PEM
• run.def and run_PEM.def A txt file specifying run parameters
• ob_ex_lsp.asc A txt files specifying orbit parameters
• data_GCM_Y1.nc A netcdf file containing information about the typical year run by the GCM

Choices of parameters (run_PEM.def)

• evol_orbit_pem: Boolean. Do you want to follow an orbital forcing predefined (read in ob_ex_lsp.asc for example)? (default=false)
• year_bp_ini: Integer. Number of year before present to start the pem run if evol_orbit_pem=.true. , default=0
• Max_iter_pem: Integer. Maximal number of iteration if none of the stopping criterion is reached and if evol_orbit_pem=.false., default=99999999
• dt_pem: Integer. Time step of the PEM in year, default=1
• alpha_criterion: Real. Acceptance rate of sublimating ice surface change, default=0.2
• soil_pem: Boolean. Do you want to run with subsurface physical processes in the PEM? default=.true.