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namelist parameter: nu_top
Laplacian smoothing applied at the model top with coefficient nu_top*nu_top_scale(k)
preqx dycore (EAM v0,v1). Sponge layer modeled after that used by CAM-EUL
nu_top=2.5e5
nu_top_scale(1:nlev)=4,2,1,0,0,0….. (applied in top 3 model layers)
Laplacian term added to RHS of hyperviscosity operator
Theta dycore (EAM v2, v3, SCREAM). Sponge layer modeled after CAM-FV ( Lauritzen et al., https://doi.org/10.1177/1094342011410088 )
nu_top = Resolution dependent. See https://acme-climate.atlassian.net/wiki/spaces/DOC/pages/1044644202/EAM+s+HOMME+dycore
Laplacian term applied independently from hyperviscosity, and with it’s own timestep controlled by hypervis_subcycle_tom. Default 1.
nu_top_scale(:) uses reference pressure based formula
Formula in terms of reference pressure computed from “eta” coordinate:
p_ratio = eta(1)/eta(k)
nu_top_scale = 16*( 1 ./ ( 1 + (p_ratio)^-2)).(mathematically equivalent to the 8*(1+ tanh(log(p_ratio))) formula used in CAM-FV)where (nu_top_scale>8) nu_top_scale=8
where (nu_top_scale<0.15) nu_top_scale=0
This formula creates a sponge layer that is active from [ptop/10,ptop]. For EAM’s 72L and 80L configuration, ptop=0.1 mb (~60 km), meaning that the sponge layer starts at 1mb which might be too high. For SCREAM’s L128 configuration, ptop=2mb, so the sponge layer starts an 20mb, which might be too low. At NE256 and 72L, the model is unstable in the sponge layer.
Simplified New simplified option with namelist control over sponge layer thickness:
To address the instabilities seen at high resolution, EAM v3 includes a new sponge layer option controlled by namelist variable
tom_sponge_start, specified in mbtom_sponge_start>0will replace the default with a simplified version of the above formula that makes it easy to control the sponge layer thickness:p_ratio = (tom_sponge_start/100) / eta(k)
nu_top_scale = .15 * p_ratio^2tom_sponge_start=1.0 reproduces the E3SMv2 72L sponger layer. tom_sponge_start=20 reproduces the SCREAM 128L
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Some aqua planet experiments looking at zonal wind and EKE at model top: /wiki/spaces/NGDNA/pages/1060077843
At NE256 (and probably higher) with EAM’s 72L configuration, the model is unstable and the sponge layer needs to be larger (but not stronger):
atm.log.* output:
EAM V3 80L configuration, Reference pressure for the first 12 levels:
1st column: interface pressure (mb)
2nd column: midpoint pressure (mb)
columns 3-6: A and B hybrid coordinate info
| Code Block |
|---|
Layer Locations (*1000)
1 0.1000 0.0000 0.1000
0.1236 0.0000 0.1236
2 0.1472 0.0000 0.1472
0.1819 0.0000 0.1819
3 0.2166 0.0000 0.2166
0.2674 0.0000 0.2674
4 0.3183 0.0000 0.3183
0.3924 0.0000 0.3924
5 0.4665 0.0000 0.4665
0.5740 0.0000 0.5740
6 0.6814 0.0000 0.6814
0.8358 0.0000 0.8358
7 0.9902 0.0000 0.9902
1.2093 0.0000 1.2093
8 1.4284 0.0000 1.4284
1.7344 0.0000 1.7344
9 2.0405 0.0000 2.0405
2.4590 0.0000 2.4590
10 2.8776 0.0000 2.8776
3.4356 0.0000 3.4356
11 3.9936 0.0000 3.9936
4.7150 0.0000 4.7150
12 5.4364 0.0000 5.4364
6.3372 0.0000 6.3372 |
V3 default sponge layer with EAM’s 80L configuration, as a function of model level k
| Code Block |
|---|
sponge layer nu_top viscosity scaling factor
nu_scale_top 1 6.32916693361379
nu_scale_top 2 3.71290112422668
nu_scale_top 3 1.96275667155077
nu_scale_top 4 0.975836740648787
nu_scale_top 5 0.471377418464948
nu_scale_top 6 0.225813746829097 |
EAM’s 72L configuration, Reference pressure for the first 6 levels:
1st column: interface pressure (Pa)
2nd column: midpoint pressure (Pa)
3rd column: layer thickness:
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| Code Block |
|---|
nu_scale_top 1 8.00000000000000 nu_scale_top 2 8.00000000000000 nu_scale_top 3 8.00000000000000 nu_scale_top 4 8.00000000000000 nu_scale_top 5 8.00000000000000 nu_scale_top 6 4.96653062623658 nu_scale_top 7 2.27814520652286 nu_scale_top 8 1.04498410914579 nu_scale_top 9 0.479333707632238 nu_scale_top 10 0.21987014085820321987014085820 |
SCREAM;'s 128L configuration:
V2 sponge layer with SCREAM’s 128L configuration, as a function of model level k
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