(A) Future of Radiation Parameterizations in CAM Bill Collins National Center for Atmospheric Research

Required Output Fields Broadband fluxes Broadband heating rates  Spectral actinic fluxes  Photosynthetically active radiation (PAR)  Spectral radiances and fluxes  Comparison against radiative observations  Non-LTE radiation fields above 60 km (?)  Adjoint of RTE or equivalent (?)

Required Features Accurate relative to accepted benchmarks Correct asymptotic behavior: –Vertical resolution   –Spectral resolution   Correct limiting behavior for ideal cases: –Conservatively scattering atmospheres –Strong and weak line limits –Single scattering and optically thick limits Correct answers for extreme (paleo) conditions “Fast” (e.g., linear in spatial resolution) “Light weight” (small memory footprint)

Desirable Features Flexible: –Add new radiative species –Enhance or degrade spectral resolution –Solve for complex condensate geometries –Test alternate solution methods Traceable: –Line & continuum absorption by gases/vapor –Intrinsic optical properties of condensates Testable: –Benchmarks provided for each component –Components can be easily tested in isolation Very Modular

Magic Numbers

The RTE for the radiance I is: Solution requires: –A specification for intrinsic optical properties: Single-scattering albedo  Phase function P Specific extinction  k e –A method for integrating over wavelength –A specification for the geometry The Radiative Transfer Equation

Intrinsic Optical Properties (Gases) Radiative active gases and H 2 O vapor: Line by line model (e.g., GENLN3) Benchmark Heating Rates Extinction k e ( ) Parameterization Error Analysis New data New d

Benchmark Calculations

Intrinsic Optical Properties (Condensate) Size Distribution Indices of Refraction Mie Calculator Discrete Dipole Approximation Size/Shape Parameter Sampling Parameterization f(r e, T, …) Scaling and Mixing Rules Anomalous Diffraction Theory Gas Optics Bulk Optical Properties Offline Online

Integration over Wavelength Correlated k: Additional features: –Hierarchical spectral resolution –Exposed methods for interpolating over vertical sub-grid variation CAM Bands

Angular Integration and Geometry Bulk Optical Properties Spatial Solver Spectral Integration Two-Stream Methods Discrete Ordinates Solver Monte Carlo… Geometry from Cloud Parameterization Lateral Boundary Conditions