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Fix for RRTMGP errors caused by high surface temperatures. #3643

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Fix for RRTMGP errors caused by high surface temperatures. #3643

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Fix for RRTMGP errors caused by high surface temperatures.
olyson Dec 2, 2025
bb86640
Human readability.
olyson Dec 3, 2025
a33f75f
Add min_lai parameter
olyson Dec 3, 2025
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Clarify comment
olyson Dec 3, 2025
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olyson Dec 3, 2025
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21 changes: 18 additions & 3 deletions src/biogeophys/CanopyFluxesMod.F90
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Original file line number Diff line number Diff line change
Expand Up @@ -437,6 +437,8 @@ subroutine CanopyFluxes(bounds, num_exposedvegp, filter_exposedvegp,
real(r8), parameter :: k_cyl_area = 1.0_r8 !departure from cylindrical area
real(r8), parameter :: k_internal = 0.0_r8 !self-absorbtion of leaf/stem longwave
real(r8), parameter :: min_stem_diameter = 0.05_r8 !minimum stem diameter for which to calculate stem interactions
real(r8), parameter :: min_lai = 0.1_r8 !minimum elai threshold to add esai to sa_leaf calculation
!value is arbitrary but has been effective in avoiding RRTMGP errors in CESM3 development simulations

integer :: dummy_to_make_pgi_happy
!------------------------------------------------------------------------------
Expand Down Expand Up @@ -745,15 +747,28 @@ subroutine CanopyFluxes(bounds, num_exposedvegp, filter_exposedvegp,
! adjust for departure of cylindrical stem model
sa_stem(p) = k_cyl_area * sa_stem(p)

!
! only calculate separate leaf/stem heat capacity for trees
! and shrubs if dbh is greater than some minimum value
! (set surface area for stem, and fraction absorbed by stem to zero)
! and shrubs if dbh is greater than some minimum value.
! otherwise, set surface area for stem and fraction absorbed by stem to zero,
! and add esai to sa_leaf.
if(.not.(is_tree(patch%itype(p)) .or. is_shrub(patch%itype(p))) &
.or. dbh(p) < min_stem_diameter) then
frac_rad_abs_by_stem(p) = 0.0_r8
sa_stem(p) = 0.0_r8
sa_leaf(p) = sa_leaf(p) + esai(p)
else
! Add esai to sa_leaf if elai is less than threshold.
! Intended to avoid small sa_leaf which leads to small leaf conductance
! and high leaf temperature. This in turn can lead to unrealistically
! high surface temperatures passed to the atmospheric model (The RRTMGP
! component in particular, which returns an error and stops the model
! if the surface temperature is greater than 355K).
! See https://github.com/ESCOMP/CTSM/issues/3589 for more info.
! The 0.1_r8 value is arbitrary but has been effective in
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@ekluzek ekluzek Dec 3, 2025

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Since this part of the comment is above, you could remove these two lines.

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@olyson olyson Dec 3, 2025

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Good point, thanks. Done.

! avoiding RRTMGP errors in CESM3 development simulations.
if(elai(p) < min_lai) then
sa_leaf(p) = sa_leaf(p) + esai(p)
endif
endif

! if using Satellite Phenology mode, calculate leaf and stem biomass
Expand Down