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, the model use an “asynchronous coupling” between the slow ice and water reservoirs models and the GCM. In practice the Planetary evolution model use a horizontal grid identical to that of the PCM, and include the same representation of the microclimate on slopes. In our case, we run the Planetary Evolution Model with an adaptative time step, 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) is obtained through a multi-annual run of the Global Climate model using the outcome of the Mars Evolution Model as initial state.

The PEM works in the following way:

Physical processes modelled

✅ Ice accumulation (Improvement possibles like changes of topography, watercaptag etc)

❌ Lag deposit, stratification (See Simon Neviere, Futur intern of Lucas)

∼ Glacier flow (CO2) , ✅ subgrid-scale slope phenomena

∼ Subsurface Ground Ice (In validation)

❌ Hydrology: lake, river, ocean, etc. (Alexandre Gauvain)

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 first typical year run by the GCM
• data_GCM_Y2.nc A netcdf file containing information about the second typical year run by the GCM

Naming convention of variables

TO DO:

• Rename variables
• Tendencies from the GCM : qsurf_GCM_tend

• Remove _slope

• ini_qsurf

• min_qsurf

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.