MPAS Dynamical Core

MPAS Technical Documentation (draft): https://www2.mmm.ucar.edu/projects/mpas/mpas_website_linked_files/MPAS-A_tech_note.pdf 

MPAS Users' Guide (namelist options):  https://www2.mmm.ucar.edu/projects/mpas/site/documentation/users_guide/appB_model_namelist.html 

Important namelist options for MPAS:

Transport:

• mpas_w_adv_order: Horizontal advection order for the vertical velocity, w. Default is 3.

• mpas_theta_adv_order: Horizontal advection order for the potential temperature, theta. Default is 3.

• mpas_scalar_adv_order: Horizontal advection order for scalars. Default is 3.

• mpas_u_vadv_order: Vertical advection order for horizontal velocities, u and v. Default is 3.

• mpas_w_vadv_order: Vertical advection order for the vertical velocity. Default is 3.

• mpas_theta_vadv_order: Vertical advection order for the potential temperature. Default is 3.

• mpas_scalar_vadv_order: Vertical advection order for scalars. Default is 3.

• mpas_positive_definite: Whether to ensure that the transport of tracers is positive-definite. Default is false.

• mpas_monotonic: Whether to ensure that the transport of tracers is monotonic. Default is true.

Timestepping

• mpas_time_integration_order: Order of RK timestepping scheme, 2 or 3. Default is 3.

• mpas_number_of_sub_steps: Number of acoustic substeps per full timestep. Default is 2.

• mpas_dynamics_split_steps: Number of transport substeps per full timestep. Default is 3.

• mpas_dt: Full timestep size. This needs to be appropriately scaled when using a small Earth.

Diffusion

• mpas_h_mom_eddy_visc2: Dimensional coefficient for Laplacian eddy diffusion of horizontal momentum. Default of 0 m^2/s.

• mpas_h_mom_eddy_visc4: Dimensional coefficient for fourth-order eddy hyperdiffusion of horizontal momentum. Default of 0 m^4/s.

• mpas_v_mom_eddy_visc2: Dimensional coefficient for Laplacian eddy diffusion of vertical momentum. Default of 0 m^2/s.

• mpas_h_theta_eddy_visc2: Dimensional coefficient for Laplacian eddy diffusion of potential temperature in the horizontal. Default of 0 m^2/s.

• mpas_h_theta_eddy_visc4: Dimensional coefficient for fourth-order eddy hyperdiffusion of potential temperature in the horizontal. Default of 0 m^4/s.

• mpas_v_theta_eddy_visc2: Dimensional coefficient for Laplacian eddy diffusion of potential temperature in the vertical. Default of 0 m^2/s.

• mpas_horiz_mixing: '2d_fixed' for constant coefficient horizontal diffusion or '2d_smagorinsky' for a coefficient that varies as a function of the flow tension and shear. Default is '2d_smagorinsky'. 

• mpas_len_disp: Horizontal length scale (in meters) for the diffusion. Set this equal to the horizontal resolution (in km) times 1000, e.g. mpasa120 -> mpas_len_disp=120000.  IMPORTANT: This value needs to be scaled when using a small Earth. E.g. mpasa120 with X=20 -> mpas_len_disp = 6000.

• mpas_visc4_2dsmag: Dimensionless scaling coefficient of (dx)^3 to obtain the 4th-order hyperdiffusion coefficient. Default is 0.05.

• mpas_smagorinsky_coef: Dimensionless coefficient relating the strain tensor and eddy viscosity for Smagorinsky diffusion. This value should be between 0.1 and 0.4. Default is 0.125.

• mpas_del4u_div_factor: Scaling factor for fourth-order hyperdiffusion, acting only on the divergent component of horizontal velocity. Default is 10.

• mpas_smdiv: 3-d divergence damping coefficient (dimensionless). Default is 0.1.

• mpas_epssm: Off-centering parameter for the vertically implicit acoustic integration (dimensionless). Default is 0.1.

• mpas_zd: Height above main sea level (in meters) which to damp the vertical velocity. Default is 22000.

• mpas_xnutr: Maximum w-damping coefficient at model top. Value is between 0 and 1. Default 0.2

• mpas_number_cam_damping_levels: Number of layers in which to apply cam 2nd-order horizontal filter near the top of model; viscosity linearly ramps to zero by layer number from the top. Default is 4.

Should this read mpas_cam_damping_levels instead of mpas_number_cam_damping_levels

• mpas_cam_coef: multiplier for the diffusion coefficient of the second-order Laplacian sponge-layer diffusion in the uppermost leyers, determined by mpas_cam_damping_levels, default is 0.2

• mpas_rayleigh_damp_u: Whether to apply Rayleigh damping on horizontal velocity in the top-most model levels (.true. or .false., default is .true.). The number of levels is specified by the mpas_number_rayleigh_damp_u_levels option, and the damping timescale is specified by the mpas_rayleigh_damp_u_timescale_days option

• mpas_rayleigh_damp_u_timescale_days: Timescale, in days, for the Rayleigh damping on horizontal velocity in the top-most model levels (if using it). Default is 5.

• mpas_number_rayleigh_damp_u_levels: Number of layers in which to apply Rayleigh damping on horizontal velocity at top of model; damping linearly ramps to zero by layer number from the top. Default is 6.

Physics-dynamics coupling