shortwave radiation options in the wrf model
DESCRIPTION
Shortwave Radiation Options in the WRF Model. An oh-so fascinating study of the Dudhia , Goddard and RRTMG shortwave schemes. Radiation in the WRF. Current Schemes: All single column, 1-D schemes – each column treated independently - PowerPoint PPT PresentationTRANSCRIPT
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Shortwave Radiation Options in
the WRF ModelAn oh-so fascinating study of the Dudhia, Goddard and RRTMG shortwave schemes
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Radiation in the WRF
Current Schemes:All single column, 1-D schemes – each column treated independentlyGood approximation if vertical depth is much less than horizontal scale
Radiation schemes resolve atmospheric heating from:Radiative flux divergenceSurface downward longwave and shortwave radiation [for ground heat]
Shortwave radiation:Includes wavelengths of solar spectrumAccounts for absorption, reflection and scattering in atmosphere and on surfacesUpward flux dependent on albedoIn atmosphere, determined by vapor/cloud content, as well as carbon dioxide, ozone and trace gas concentrations
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Dudhia Scheme ra_sw_physics = 1
Based on Dudhia 1989, from MM5
Uses look-up tables for clouds from Stephens 1978
Version 3 has option to account for terrain slope and shadowing effects on the surface solar flux
Simple downward integration of solar flux, which accounts for:
Clear air scatteringWater vapor absorption [Lacis and Hansen, 1974]Cloud albedo and absorption
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Goddard Schemera_sw_physics = 2
Based on Chou and Suarez 1994
Includes 11 spectral bands
Different climatological profiles available for numerous ozone options
Considers both diffuse and direct solar radiation in 2-stream approach, accounts for scattering and reflection
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RRTMG Schemera_sw_physics = 4
Uses MCICA [Monte Carlo Independent Column Approximation] method of random cloud overlap – statistical method to resolve sub-grid scale cloud variability
Finer resolution runs usually associated with WRF model means that clouds will most likely take up the entire grid space [binary clouds], in which case MCICA will not work.
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Temperature
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Relative Humidity
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Zonal Winds
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Meridional Winds
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Vertical Winds
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Top of Atmosphere Radiation
Longwave Radiation Upward
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Top of Atmosphere Radiation
Longwave Radiation Upward Differences
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Surface RadiationLongwave
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Surface RadiationLongwave Differences
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Surface RadiationShortwave
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Surface RadiationShortwave Differences
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Surface RadiationLongwave Radiation Upward
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Surface RadiationLongwave Radiation Upward
Differences
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Surface RadiationLongwave Radiation Downward
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Surface RadiationLongwave Radiation Downward
Differences
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Surface Heat FluxGround Heat
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Surface Heat FluxGround Heat Differences
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Surface Heat FluxSensible Heat
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Surface Heat FluxSensible Heat Differences
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Surface Heat FluxLatent Heat
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Surface Heat FluxLatent Heat Differences
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Significant Variations and
ConclusionsGoddard Scheme (ra_sw_physics=2) initialized differently and gave the most extreme values
Most variations were insignificant, other than mid-level drying in RRTMG scheme.
Much larger flux differences arise if clouds are sparse or absent during peak diurnal heating
Surface fluxesClear sky conditions – algorithmic differences in handling gaseous absorption/emission of longwave radiation and extinction of shortwave radiationDifferences in initial concentrations of trace gasesDifferences in allowable cloud fractions
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Resources“Assessment of Radiation Options in the Advances Research WRF Weather Forecast Model”, Iacono and Nehrkorn
“A Description of the Advanced Research WRF Version 3”, Skamarock et al.