Parameterizing Soil Albedo

We currently support two parameterizations for the soil albedo. These

options are defined using Julia types, using simplified code, as follows.

We first introduce the abstract type AbstractSoilAlbedoParameterization,

and then the two albedo parameterizations are concrete examples of that

abstract type:

ConstantTwoBandSoilAlbedo <: AbstractSoilAlbedoParameterization
CLMTwoBandSoilAlbedo <: AbstractSoilAlbedoParameterization

Each of these types define a method for update_albedo!, which is

called in the soils tendency functions, and each stores the

parameters required to compute the albedo for that parameterizations.

For example, the parameterization based off of CLM's approach requires

the wet and dry soil albedos in the PAR and NIR wavelength bands. For

each band, the actual albedo is a linear combination of the wet and dry

values, with a weight depending on the soil moisture. The method

of update_albedo! for this parameterization computes this linear

combination using a helper function albedo_from_moisture and ultimately

sets

@. p.soil.PAR_albedo =
    albedo_from_moisture(S_sfc, PAR_albedo_dry, PAR_albedo_wet)
@. p.soil.NIR_albedo =
    albedo_from_moisture(S_sfc, NIR_albedo_dry, NIR_albedo_wet)
````
where `S_sfc` is the effective saturation at the surface.

### Creating a new albedo parameterization

# Suppose you want to define a new parameterization which models albedo
# as a linear combination of the albedos of quartz, organic matter, minerals
# and water, treating NIR and PAR albedos the same.

# First, create the type:

julia struct SoilAlbedoFromComposition{FT <: AbstractFloat} <: AbstractSoilAlbedoParameterization αquartz::FT αminerals::FT αom::FT αwater::FT end

# And then create the method. For now, don't worry about the other arguments
# and their types:

julia function updatealbedo!( bc::AtmosDrivenFluxBC, albedo::SoilAlbedoFromComposition, p, soildomain, modelparameters, ) # unpack parameters of the albedo model (; αquartz, αminerals, αom, αwater) = albedo # unpack composition parameters from the soil parameters (; νssom, νssquartz) = modelparameters # Extract the values at the top level νssomsfc = ClimaLand.Domains.topcentertosurface(νssom) νssquartzsfc = ClimaLand.Domains.topcentertosurface(νssquartz) # Extract the top layer's volumetric water content θlsfc = ClimaLand.Domains.topcentertosurface(p.soil.θl)

# Compute the linear combination
@. p.soil.PAR_albedo = α_water * θ_l_sfc + (1-θ_l_sfc)* (α_quartz * ν_ss_quartz_sfc + α_om * ν_ss_om_sfc + α_minerals * (1-ν_ss_om - ν_ss_quartz))
p.soil.NIR_albedo .= p.soil.PAR_albedo

end ```