EAM and SCREAM uses the HOMME dycore package which contains the EAM v1 hydrostatic dycore (PREQX) and the proposed v2 nonhydrostatic dycore (THETA). These dycores share much of the HOMME infrastructure and have several timesteps:
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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.
Recommended settings (THETA)
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Resolution | Timesteps | Namelist settings | Notes | Tested? |
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1 degree (NE30) | dtime=1800 1800 (ATM_NCPL=72) dt_remaptracer=6001800 | nu=1e15 se_tstep=300 | 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 F-EAMv1-AQP1: H and NH FAV1C-L: H and NH |
1/4 degree (NE120) | dtime=900 (ATM_NCPL=144) dt_remap=150 | nu=1.5e13 se_tstep=75 | 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=480? dt_remaptracer=80300 | nu=1.6e12 dt_tracer_factor=8 | nu_tom=4e4 is running at the code's estimate of the CFL limit with S=1.9dt=dt_dyn/ dt_remap/ dt_tracer / dt_phys | F-EAMv1-AQP1:
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6km (NE512) | dtime=300 (ATM_NCPL=288) dt_ remaptracer= 40150 remap= 12037. .1805 18.75 18.75 | 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:
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3km (NE1024) | dtime=150 (ATM_NCPL=576) dt_remaptracer=2075 | 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:
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PREQX Default Settings (for reference)
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