Spectral Element (SE) Dynamical Core

Important namelist options for SE:

Transport:

• se_limiter_option: Limiting of the tracer transport. 0 for no limiter, 4 for sign-preserving, 8 for monotonic. Default is 8.

Timestepping

• se_tstep_type: The timestepping scheme.1 is RK2 with leapfrog, 2 is a three-stage SSP-RK2, 3 is classic RK3, 4 is a five-stage third-order SSPRK scheme. Default of 4.

• se_nsplit: The number of dynamics substeps within each physics timestep. Default is 2.

• se_qsplit: The number of tracer transport substeps within each dynamics timestep. Default is 1.

• se_rsplit: The number of vertical Lagrangian remappings per tracer transport timestep. Default is 3.

• se_hypervis_subcycle: The number of hyperviscosity substeps per dynamics timestep. 

• se_hypervis_subcycle_sponge: The number of hyperviscosity substeps in the sponge layer per dynamics timestep.  

• se_hypervis_subcycle_q: The number of hyperviscosity substeps for tracer transport per dynamics timestep.  

Diffusion

 Note that these are dimensional and so should change with horizontal resolution, such as moving from ne30 to ne60 or using a small Earth.

• se_nu: Coefficient of fourth-order hyperviscosity for horizontal velocities and temperature. 

• se_nu_div: Coefficient of fourth-order hyperviscosity for horizontal divergence

• se_nu_p: Coefficient of fourth-order hyperviscosity for pressure-level thickness

• se_nu_top: Coefficient of Laplacian diffusion for the sponge layer in the upper region of the domain

• se_hypervis_scaling: Determines the power of scaling for the hyperviscosity coefficients. If 0, hyperviscosity coefficients are constant coefficients with units of m^4/s and must be properly scaled according to resolution and time step. A value of 3.0 is tensor hyperviscosity and is scale-aware. If tensor hyperviscosity is used then hyperviscosity coefficients are in units of 1/s, and only require a 1/X scaling for reduced Earth models, where X is the reduce Earth scale factor. See Guba et. al 2014 (doi:10.5194/gmd-7-2803-2014) for more details. Default is 0 (const. coeff) in hydrostatic SE. Default is 3 (tensor) in StormSPEED.

Physics-dynamics coupling

• se_ftype: The option for physics-dynamics coupling. 0 is tendencies, where the full physics timestep forcing is split into equal chunks and applied at each vertical remapping timestep. 1 is 'adjustments', where the full physics forcing is applied all-at-once. 2 is a hybrid of both, using the tendency approach for tracers (mixing ratios) and adjustments for all other variables.

StormSPEED only:

StormSPEED has a different approach to setting the time steps that replaces the nsplit, rsplit, qsplit namelist variables used in the normal SE time splitting namelists.

• se_tstep: The dynamic time step in seconds. Replaces nsplit, qsplit, rsplit.

• se_dt_remap_factor: The tracer advection timestep is dt_tracer_factor*se_tstep. dt_tracer_factor*se_tstep must divide the physics time, and one of dt_remap_factor and dt_tracer_factor must divide the other. Replaces qsplit, rsplit. Default is 2.

• se_dt_tracer_factor: The vertically Lagrangian remap timestep is dt_remap_factor*se_tstep. dt_remap_factor*se_tstep must divide dtime, and one of dt_remap_factor and dt_tracer_factor must divide the other. Replaces qsplit, rsplit. Default is 6.

• se_tom_sponge_start: While this variable is in the namelist definitions, it currently is not implemented. To control the size of the sponge layer in SE StormSPEED, a SourceMod of model_init_mod.F90 is required. For the squall line test case it is implemented so that the sponge starts at approximately 150 hPa.