A Future of Radiation Parameterizations in CAM

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(A) Future of Radiation Parameterizations in CAM

• Bill Collins
• National Center for Atmospheric Research
• www.cgd.ucar.edu/wcollins

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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 (?)

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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)

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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

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Magic Numbers
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The Radiative Transfer Equation

• The RTE for the radiance I is
• Solution requires
• A specification for intrinsic optical properties
• Single-scattering albedo ?
• Phase function P
• Specific extinction ? ke
• A method for integrating over wavelength
• A specification for the geometry

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Intrinsic Optical Properties (Gases)

• Radiative active gases and H2O vapor

Line by line model (e.g., GENLN3)
New data
Extinction ke(?)
New d?
Benchmark Heating Rates
Parameterization
Error Analysis
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Benchmark Calculations
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Intrinsic Optical Properties (Condensate)
Scaling and Mixing Rules
Bulk Optical Properties
Gas Optics
Online
Offline
Parameterization f(re, T, )
Size/Shape Parameter Sampling
Size Distribution
Mie Calculator
Discrete Dipole Approximation
Anomalous Diffraction Theory
Indices of Refraction
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Integration over Wavelength

• Correlated k
• Additional features
• Hierarchical spectral resolution
• Exposed methods for interpolating over vertical
  sub-grid variation

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