AnalyticBandRadiation.jl

Analytic-band atmospheric radiation for intermediate-complexity models.

This package bundles two per-column radiation schemes:

• Longwave — Williams (2026) Simple Spectral Model: a 41-wavenumber clear-sky two-stream Schwarzschild solver with analytic H₂O line, H₂O continuum and CO₂ absorption coefficients. Published in J. Adv. Model. Earth Syst., doi:10.1029/2025MS005405.
• Shortwave — a one-band scheme after SPEEDY (Kucharski, Molteni & Bracco, Quart. J. Roy. Meteor. Soc., 2006), with transparent, constant, or Kucharski-style background-transmissivity options and a diagnostic cloud/stratocumulus model.

The column solvers are pure scalar operations — no allocations, no host-side loops, GPU-safe — so the same code can be driven by SpeedyWeather.jl (which dispatches per column via parameterization!(ij, vars, scheme, model)) or by Breeze (which launches a KernelAbstractions kernel per column inside _update_radiation!).

Package extensions wire each host automatically when both packages are loaded.

Installation

using Pkg
Pkg.add(url="https://github.com/NumericalEarth/AnalyticBandRadiation.jl")

Standalone usage (single column)

Bundle the grid, profile, surface, schemes, constants, and pre-allocated buffers into a single RadiativeTransferColumn and call the solvers with one argument:

using AnalyticBandRadiation

nlayers = 8
σ_half  = collect(range(0.0, 1.0, length = nlayers + 1))
grid    = ColumnGrid(σ_half)

# Lapse-rate profile: top of atmosphere (k=1) cold, surface (k=nlayers) warm.
profile = AtmosphereProfile(
    temperature      = collect(range(220.0, 295.0, length = nlayers)),
    humidity         = fill(0.005, nlayers),
    geopotential     = zeros(nlayers),
    surface_pressure = 100_000.0,
    CO₂              = 280.0,
)

surface = SurfaceState(
    sea_surface_temperature  = 295.0,
    land_surface_temperature = 285.0,
    land_fraction            = 0.3,
    ocean_albedo             = 0.07,
    land_albedo              = 0.25,
    cos_zenith               = 0.5,
)

# Schemes, constants, and output buffers all wrap up here.
rtm = RadiativeTransferColumn(; grid, profile, surface)

solve_longwave!(rtm)
solve_shortwave!(rtm)

@show rtm.longwave_diagnostics.outgoing_longwave        # W m⁻²
@show rtm.longwave_diagnostics.surface_longwave_down    # W m⁻²
@show rtm.shortwave_diagnostics.surface_shortwave_down  # W m⁻²
@show rtm.temperature_tendency                           # K s⁻¹ per layer

For the low-level kernel form (what hosts like SpeedyWeather / Breeze extensions call internally), solve_longwave! and solve_shortwave! accept the flattened (dTdt, diagnostics, scheme, profile, grid, surface, constants, …) signature directly, and the constants argument is duck-typed — any struct or NamedTuple carrying gravity, heat_capacity, stefan_boltzmann, solar_constant properties works.

All floating-point types default to Float64. To run in Float32 (useful for GPU kernels), pass the type as a positional argument to the scheme constructors: AnalyticBandLongwave(Float32), OneBandShortwave(Float32), etc.

With SpeedyWeather.jl

The AnalyticBandRadiationSpeedyWeatherExt extension defines a SpeedyAnalyticBandLongwave scheme that subtypes SpeedyWeather.AbstractLongwave and can be passed directly to PrimitiveWetModel:

using SpeedyWeather, AnalyticBandRadiation
const SpeedyExt = Base.get_extension(AnalyticBandRadiation,
                                     :AnalyticBandRadiationSpeedyWeatherExt)

spectral_grid = SpectralGrid(trunc = 31, nlayers = 8)
longwave      = SpeedyExt.SpeedyAnalyticBandLongwave(spectral_grid)
model         = PrimitiveWetModel(spectral_grid; longwave_radiation = longwave)

With Breeze

The Breeze extension is a scaffold: it defines SpectralOptics, the RadiativeTransferModel(grid, ::SpectralOptics, constants; …) constructor, and the kernel skeleton. Full integration (ZFaceField flux allocation, reference-pressure plumbing, surface albedo handling) is tracked as a follow-up and will mirror the BreezeRRTMGPExt gray-radiation constructor.

Schemes at a glance

Scheme	Purpose	References
WilliamsLongwave	41-band clear-sky LW	Williams (2026); Armstrong (1968); Mlawer et al. (1997)
TransparentShortwave	Zero-atmosphere SW; surface-albedo only	—
OneBandShortwave	SPEEDY moist SW (diagnostic clouds + background transmissivity)	Kucharski, Molteni & Bracco (2006)
OneBandGreyShortwave	SPEEDY dry SW (no clouds, constant transmissivity)	Kucharski, Molteni & Bracco (2006)
DiagnosticClouds	Cloud cover from RH + precipitation; stratocumulus from DSE stability	SPEEDY §B4
BackgroundShortwaveTransmissivity	Dry-air + aerosol + WV + cloud absorptivities, pressure-weighted	SPEEDY §B4
ConstantShortwaveTransmissivity	Single-value column transmissivity	—

Tests

julia --project=. -e 'using Pkg; Pkg.test()'

License

MIT. See LICENSE.