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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 coefficients need to be slightly reduced.  




Recommended settings (THETA)   

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  • theta_hydrostatic_mode=.false., tstep_type=9
ResolutionTimestepsNamelist settingsNotesTested?
1 degree (NE30)

dtime=1800  (ATM_NCPL=72)

dt_remap=600
dt_tracer=1800
dt_dyn=dt_vis=dt_vis_q=300
dt_vis_tom=300



nu=1e15
nu_top = 2.5e5    

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
dt_tracer=450
dt_dyn=dt_vis=dt_vis_q=75
dt_vis_tom=75

nu=1.5e13
nu_top=1e5

se_tstep=75



CFL estimates suggest:

dt_vis_tom*nu_top <= 31*2.5e5

nu_top=2.5e5 would need
hypervis_subcycle_tom=3


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?
ATM_NCPL=180

dt_remap=80
dt_tracer=240
dt_dyn=dt_vis=dt_vis_q=40
dt_vis_tom = 40

nu=1.6e12
nu_top=4e4
se_tstep=40





nu_tom=4e4 is running at the code's estimate of the CFL limit with S=1.9

dt=dt_dyn/ dt_remap/ dt_tracer / dt_phys

F-EAMv1-AQP1:
H-128L running with default timesteps. (1 month)  

NH-128L:

some issues with tstep=40, crashes
  • tstep_type=9:  Runs with dt=37.5/75/300/600.  crashes with dt=40/40/240/480 after 6d, dp3d<0 around layer 30.   
Best stable settings as of (ran 1 month):  se_tstep=30, dt_remap_factor=8
  • with tstep_type=10:  


6km (NE512)dt_remap=40
dt_tracer=120  
dt_dyn=dt_vis=dt_vis_q=20
dt_vis_tom=20

nu=2e11
nu_top=2e4
se_tstep=20



CFL estimates suggest:

dt_vis_tom*nu_top <= 1.7*2.5e5,

nu_top=2.5e5 needs hypervis_subcycle_tom=13 

F-EAMv1-AQP1:
NH-128L: testing with default settings

3km (NE1024)

dt_remap=20
dt_tracer=60 
dt_dyn=dt_vis=dt_vis_q=10
dt_vis_tom=10

nu=2.5e10
nu_top=1e4
se_tstep=10


CFL estimates suggest:

dt_vis_tom*nu_top <= 0.43*2.5e5

with nu_top=2.5e5, 
hypervis_subcycle_tom=24







PREQX Default Settings (for reference)

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