EAM and SCREAM uses the HOMME dycore package. HOMME has both Fortran and C++ versions with different options for the prognostic thermodynamic variable (preqx use temperaturee while theta-l uses potential temperature) and those in turn have some additional capabilities.
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An additional constraint is that either dt_remap must evenly divide dt_tracer or dt_tracer must evenly divide dt_remap.
Using the new or old namelist settings
When running in EAM, the CIME case control system will set the correct defaults based on CAM_TARGET, using the old namelist settings for preqx and the new namelist settings for theta-l. Cases using the theta-l dycore should then use the new namelist variables in user_nl_cam if changes are needed. Cases using the preqx dycore should use the old namelist variables in user_nl_cam.
To use the new namelist variables with the preqx dycore, (or in standalone HOMME), one should set nsplit=-1, rsplit=-1 and qsplit=-1
CFL Conditions
dt_dyn: The CFL condition for dt_dyn with uniform resolutions is well understood and depends on the horizontal resolution and the speed of the Lamb wave (~340m/s). This assumes the use of the KG5 RK method (tstep_type=5) for hydrostatic, and the related IMEX method (tstep_type=9 or 10) for NH.
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With RRM grids, the timesteps will be controlled by the highest resolution region. So with an RRM grid with refinement down to NE120, the timesteps should be close to what we run on a uniform cubed-sphere NE120 grid. The timesteps may need to be slightly smaller because of the deformed elements in the transition region. With a hiqh quality RRM mesh ( Max Dinv-based element distortion metric <= 4, see Generate the Grid Mesh (Exodus) File for a new Regionally-Refined Grid) we can usually run with the expected dt_dyn and dt_tracer values, and only the viscosity timesteps need to be slightly reduced.
Spreadsheet for looking at scaling with resolution of constant and tensor coefficient HV:
https://docs.google.com/spreadsheets/d/1LHTl2_A065pfdWC69OHmXvNL_v1484cXg7ZowhyEbPU/edit?usp=sharing
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| Resolution | Timesteps | Namelist settings | Notes | Tested? |
|---|---|---|---|---|
| 1 degree (NE30) | dtime=1800 (ATM_NCPL=48) dt_tracer=1800 | nu=1e15 se_tstep=300 dt_tracer_factor = 6 | With dt_remap=1800, we see occasional (every 2-3 years) dp3d limiter activation, meaning that the model levels are approaching zero. This appears to be due to strong divergence above tropical cyclones created by one of the parameterizations. | HS+topo(72L): H and NH (H can run at t 360s but not 400s with either tstep_type=4 or 5). dt_remap=600 runs with no limiter warnings, while dt_remap=900 crashes with dp3d<0 at surface. F-EAMv1-AQP1: H and NH FAV1C-L: H and NH |
| NE45 | dtime=1200. (ATM_NCPL=72) dt_tracer=1200 dt_vis_tom=200 | nu=3e14 se_tstep=200 | ||
| 1/4 degree (NE120) | dtime=900 (ATM_NCPL=96) dt_remap=150 | nu=1.5e13 se_tstep=75 dt_tracer_factor = 6 | CFL estimates suggest: dt_vis_tom*nu_top <= 31*2.5e5 nu_top=2.5e5 would need | HS+topo(72L): H and NH (with dt_remap=75 and theta limiter to handle unphysical boundary layer) F-EAMv1-AQP1: H and NH, both 72 and 128 levels (1+ years) FC5AV1C-H01B: NH 72L runs several years. |
12km (NE256) | dtime=600 (ATM_NCPL=144) dt_tracer=300 | nu=1.6e12 dt_tracer_factor=8 | nu_tom=4e4 is running at the code's estimate of the CFL limit with S=1.9 | F-EAMv1-AQP1:
FC5AV1C-H01B: NH 128L run for several months dt=37.5/75/300/600. Occasional problems near coastlines - considering ( ) reducing dtime, increasing HV, tunning CLUBB |
| 6km (NE512) | dtime=300 (ATM_NCPL=288) dt_tracer=150 | nu=2e11 dt_tracer_factor=8 | CFL estimates suggest: dt_vis_tom*nu_top <= 1.7*2.5e5, nu_top=2.5e5 needs hypervis_subcycle_tom=13 | F-EAMv1-AQP1:
FC5AV1C-H01B: NH 128L run for 1 day with dt=18.75/37.5/150/300, then NaNs in microphysics (not yet debugged) |
| 3km (NE1024) | dtime=150 (ATM_NCPL=576) dt_tracer=75 | nu=2.5e10 dt_tracer_factor=8 | CFL estimates suggest: dt_vis_tom*nu_top <= 0.43*2.5e5 with nu_top=2.5e5, | F-EAMv1-AQP1:
FC5AV1C-H01B: SCREAM physics: run for several days with dt=9.375/18.75/75/75. Frequent (daily) problems near coastlines - considering ( ) different topography, reducing dtime, increasing HV |
| RRM | dtime=? dycore timesteps should be set based on the finest region in the RRM. | hypervis_scaling=3.0 nu=3.4e-8 nu_top=Uncertain - needs more research. Should probably switch to tensor laplacian. For NE30→NE120 grids, start with NE120 constant coefficient value, 1e5. | RRM uses a tensor HV formulation which scales with resolution dx^3.0 (For preqx, we used a dx^3.2 scaling. ) To determine the effective HV coefficient at a given resolution "dx", use: nu_tensor = nu_const *( 2*rearth /((np-1)*dx))^{hv_scaling} * rearth^{-4.0}. i.e. tensor nu=3.4e-8 when used at 1 degree resolution (dx=110,000m, np=4, rearth=6.376e6) is equivalent to 1e15 m^4/s. |
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- SE Atmosphere Grid Overview (EAM & CAM)
- Plotting data on SE native grid
- KE Spectra - best practices
- Transition to TempestRemap for Atmosphere grids
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