Address bug in specification of organic matter fraction - #8629
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…ared formulation, following CLM5.0 and Lawrence and Slater (2008). Also ensure om_frac does not exceed 1.
Add squareomfrac namelist option with default value true to allow selection between squared and unsquared organic matter fraction calculations in soil physics. When true (default), uses (organic3d/organic_max)**2 for backward compatibility. When false, uses min(organic3d/organic_max, 1.0) following CLM5.0 and Lawrence and Slater (2008).
When squareomfrac is false, change om_frac calculation to use max(0.0_r8, min(organic3d/organic_max, 1.0_r8)) to ensure the value is bounded between 0 and 1, preventing potential negative values.
…ement Add squareomfrac to namelist_defaults.xml with default value .true., and add it to the elm_varctl use statement in controlMod.F90. Also add logging output for the squareomfrac value.
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There appears to be a bug in
SoilHydrologyType.F90andSoilStateType.F90during initialization that squares the organic matter fraction whenmore_vertlayers .eq. falsebut not whenmore_vertlayers .eq. truethat came over when E3SM was initialized. This appears to be applied only to places whereom_fracmodifies thermal_conductivity, meaning thatom_fraccan be different in different places in the code. (h/t @gretamiller for finding this issue and working on the solution)The
more_vertlayers .eq. truebranch is the correct one based on the Slater and Lawrence (2008) implementation of this feature, and the bug has been fixed in upstream CLM.However, by default,
more_vertlayers .eq. falseand so the default configuration will underestimate the organic matter fraction except at 0 and 1, and therefore likely be too conductive. @gretamiller reached out to David Lawrence and confirmed that this was essentially a tuning knob to compensate for other issues in the soil when it was implemented.This fix allows turning off this "squared" relationship with a namelist option, and as a result, the e3sm_land_developer suite is BFB on pm-cpu.