CliMA · juliasloan25 · Oct 31, 2025
diff --git a/docs/src/fieldexchanger.md b/docs/src/fieldexchanger.md
@@ -39,6 +39,6 @@ the atmosphere and each surface model.
 
 ```@docs
     ClimaCoupler.FieldExchanger.combine_surfaces!
-    ClimaCoupler.FieldExchanger.resolve_ocean_ice_fractions!
+    ClimaCoupler.FieldExchanger.resolve_area_fractions!
     ClimaCoupler.FieldExchanger.import_atmos_fields!
 ```
diff --git a/experiments/ClimaEarth/components/ocean/oceananigans.jl b/experiments/ClimaEarth/components/ocean/oceananigans.jl
@@ -41,7 +41,7 @@ Specific details about the default model configuration
 can be found in the documentation for `ClimaOcean.ocean_simulation`.
 """
 function OceananigansSimulation(
-    area_fraction,
+    boundary_space,
     start_date,
     stop_date;
     output_dir,
@@ -138,7 +138,7 @@ function OceananigansSimulation(
     lat_cc = reshape(lat_cc, 1, length(lat_cc))
     target_points_cc = @. CC.Geometry.LatLongPoint(lat_cc, long_cc)
     # TODO: We can remove the `nothing` after CC > 0.14.33
-    remapper_cc = CC.Remapping.Remapper(axes(area_fraction), target_points_cc, nothing)
+    remapper_cc = CC.Remapping.Remapper(boundary_space, target_points_cc, nothing)
 
     # Construct two 2D Center/Center fields to use as scratch space while remapping
     scratch_cc1 = OC.Field{OC.Center, OC.Center, Nothing}(grid)
@@ -176,20 +176,23 @@ function OceananigansSimulation(
         ocean.output_writers[:diagnostics] = netcdf_writer
     end
 
+    # Create a dummy area fraction that will get overwritten in `update_surface_fractions!`
+    area_fraction = ones(boundary_space)
+
     sim = OceananigansSimulation(ocean, area_fraction, ocean_properties, remapping)
     return sim
 end
 
 """
-    FieldExchanger.resolve_ocean_ice_fractions!(ocean_sim, ice_sim, land_fraction)
+    FieldExchanger.resolve_area_fractions!(ocean_sim, ice_sim, land_fraction)
 
 Ensure the ocean and ice area fractions are consistent with each other.
 This matters in the case of a LatitudeLongitudeGrid, which is only
 defined between -80 and 80 degrees latitude. In this case, we want to
 set the ice fraction to `1 - land_fraction` on [-90, -80] and [80, 90]
 degrees latitude, and make sure the ocean fraction is 0 there.
 """
-function FieldExchanger.resolve_ocean_ice_fractions!(
+function FieldExchanger.resolve_area_fractions!(
     ocean_sim::OceananigansSimulation,
     ice_sim,
     land_fraction,
@@ -206,7 +209,8 @@ function FieldExchanger.resolve_ocean_ice_fractions!(
         polar_mask .= abs.(lat) .>= FT(80)
 
         # Set ice fraction to 1 - land_fraction and ocean fraction to 0 where polar_mask is 1
-        @. ice_fraction = ifelse.(polar_mask == FT(1), FT(1) - land_fraction, ice_fraction)
+        @. land_fraction = ifelse.(polar_mask == FT(1), FT(1), land_fraction)
+        @. ice_fraction = ifelse.(polar_mask == FT(1), FT(0), ice_fraction)
         @. ocean_fraction = ifelse.(polar_mask == FT(1), FT(0), ocean_fraction)
     end
     return nothing

diff --git a/experiments/ClimaEarth/components/ocean/prescr_ocean.jl b/experiments/ClimaEarth/components/ocean/prescr_ocean.jl
@@ -42,7 +42,7 @@ end
         ::Type{FT},
         space,
         start_date,
-        area_fraction,
+        t_start,
         thermo_params,
         comms_ctx;
         z0m = FT(5.8e-5),
@@ -65,7 +65,6 @@ function PrescribedOceanSimulation(
     space,
     start_date,
     t_start,
-    area_fraction,
     thermo_params,
     comms_ctx;
     z0m = FT(5.8e-5),

diff --git a/experiments/ClimaEarth/components/ocean/prescr_seaice.jl b/experiments/ClimaEarth/components/ocean/prescr_seaice.jl
@@ -119,12 +119,8 @@ function PrescribedIceSimulation(
     )
 
     # Get initial SIC values and use them to calculate ice fraction
-    SIC_init = CC.Fields.zeros(space)
-    evaluate!(SIC_init, SIC_timevaryinginput, tspan[1])
-
-    # Overwrite ice fraction with the static land area fraction anywhere we have nonzero land area
-    #  max needed to avoid Float32 errors (see issue #271; Heisenbug on HPC)
-    ice_fraction = @. max(min(SIC_init, FT(1) - land_fraction), FT(0))
+    ice_fraction = CC.Fields.zeros(space)
+    evaluate!(ice_fraction, SIC_timevaryinginput, tspan[1])
 
     params = IceSlabParameters{FT}()
 

diff --git a/experiments/ClimaEarth/components/ocean/slab_ocean.jl b/experiments/ClimaEarth/components/ocean/slab_ocean.jl
@@ -65,7 +65,6 @@ function SlabOceanSimulation(
     dt,
     saveat,
     space,
-    area_fraction,
     thermo_params,
     stepper = CTS.RK4(),
     evolving = true,
@@ -80,7 +79,7 @@ function SlabOceanSimulation(
         F_turb_energy = CC.Fields.zeros(space),
         SW_d = CC.Fields.zeros(space),
         LW_d = CC.Fields.zeros(space),
-        area_fraction = area_fraction,
+        area_fraction = ones(space),
         thermo_params = thermo_params,
         α_direct = CC.Fields.ones(space) .* params.α,
         α_diffuse = CC.Fields.ones(space) .* params.α,

diff --git a/experiments/ClimaEarth/setup_run.jl b/experiments/ClimaEarth/setup_run.jl
@@ -357,14 +357,11 @@ function CoupledSimulation(config_dict::AbstractDict)
             sic_path = subseasonal_sic,
         )
 
-        ## ocean model using prescribed data
-        ice_fraction = Interfacer.get_field(ice_sim, Val(:area_fraction))
-        ocean_fraction = FT(1) .- ice_fraction .- land_fraction
-
+        ## ocean model
         if sim_mode <: CMIPMode
             stop_date = date(tspan[end] - tspan[begin])
             ocean_sim = OceananigansSimulation(
-                ocean_fraction,
+                boundary_space,
                 start_date,
                 stop_date;
                 output_dir = dir_paths.ocean_output_dir,
@@ -376,7 +373,6 @@ function CoupledSimulation(config_dict::AbstractDict)
                 boundary_space,
                 start_date,
                 t_start,
-                ocean_fraction,
                 thermo_params,
                 comms_ctx;
                 sst_path = subseasonal_sst,
@@ -413,7 +409,6 @@ function CoupledSimulation(config_dict::AbstractDict)
             dt = component_dt_dict["dt_ocean"],
             space = boundary_space,
             saveat = saveat,
-            area_fraction = (FT(1) .- land_fraction), ## NB: this ocean fraction includes areas covered by sea ice (unlike the one contained in the cs)
             thermo_params = thermo_params,
             evolving = evolving_ocean,
         )
@@ -428,6 +423,7 @@ function CoupledSimulation(config_dict::AbstractDict)
     =#
 
     ## collect component model simulations that have been initialized
+    @assert (ocean_sim isa SlabOceanSimulation && isnothing(ice_sim)) "SlabOceanSimulation should not be used with sea ice, got $(ice_sim)"
     model_sims = (; atmos_sim, ice_sim, land_sim, ocean_sim)
     model_sims =
         NamedTuple{filter(key -> !isnothing(model_sims[key]), keys(model_sims))}(model_sims)
@@ -536,6 +532,7 @@ function CoupledSimulation(config_dict::AbstractDict)
         =#
 
         # 1. Make sure surface model area fractions sum to 1 everywhere.
+        #  Note that ocean and ice fractions are not accurate until after this call.
         FieldExchanger.update_surface_fractions!(cs)
 
         # 2. Import atmospheric and surface fields into the coupler fields,

diff --git a/experiments/ClimaEarth/test/component_model_tests/prescr_ocean_tests.jl b/experiments/ClimaEarth/test/component_model_tests/prescr_ocean_tests.jl
@@ -33,7 +33,6 @@ end
         space,
         start_date,
         t_start,
-        area_fraction,
         thermo_params,
         comms_ctx,
     )

diff --git a/src/FieldExchanger.jl b/src/FieldExchanger.jl
@@ -16,7 +16,7 @@ export update_sim!,
     exchange!,
     set_caches!,
     update_surface_fractions!,
-    resolve_ocean_ice_fractions!
+    resolve_area_fractions!
 
 """
     update_surface_fractions!(cs::Interfacer.CoupledSimulation)
@@ -71,7 +71,7 @@ function update_surface_fractions!(cs::Interfacer.CoupledSimulation)
 
         # ensure that ocean and ice fractions are consistent
         if haskey(cs.model_sims, :ice_sim)
-            resolve_ocean_ice_fractions!(ocean_sim, cs.model_sims.ice_sim, land_fraction)
+            resolve_area_fractions!(ocean_sim, cs.model_sims.ice_sim, land_fraction)
         end
     else
         cs.fields.scalar_temp1 .= 0
@@ -84,15 +84,15 @@ function update_surface_fractions!(cs::Interfacer.CoupledSimulation)
 end
 
 """
-    resolve_ocean_ice_fractions!(ocean_sim, ice_sim, land_fraction)
+    resolve_area_fractions!(ocean_sim, ice_sim, land_fraction)
 
 Ensure that the ocean and ice fractions are consistent with each other.
 For most ocean and ice models, this does nothing since the ocean fraction is
 defined as `1 - ice_fraction - land_fraction`. However, some models may have
 additional constraints on the ice and ocean fractions that need to be enforced.
 This function can be extended for such models.
 """
-function resolve_ocean_ice_fractions!(ocean_sim, ice_sim, land_fraction)
+function resolve_area_fractions!(ocean_sim, ice_sim, land_fraction)
     return nothing
 end