Page Comparison

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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, 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 option with control over sponge layer thickness:

  • To address the instabilities seen at high resolution, we propose to add EAM v3 includes a new sponge layer option controlled by namelist variable tom_sponge_start, specified in mb

  • tom_sponge_start>0 will replace the default with a simplified version of the above formula that makes it easy to control the sponge layer thickness:

    https://github.com/mt5555/E3SM/tree/

    • p_ratio = (tom_sponge_start/100) / eta(k)

    • nu_top_scale = .15 * p_ratio^2

    git branch:

    • tom_sponge_start=1.0 reproduces the E3SMv2 72L sponger layer. tom_sponge_start=20 reproduces the SCREAM 128L

Plots of the CAM-FV / EAMv2 sponge layer profile:

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