Presentation on theme: "Shortwave Radiation Options in the WRF Model"— Presentation transcript:
1 Shortwave Radiation Options in the WRF Model An oh-so fascinating study of the Dudhia, Goddard and RRTMG shortwave schemes
2 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 scaleRadiation 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
3 Dudhia Scheme ra_sw_physics = 1 Based on Dudhia 1989, from MM5Uses look-up tables for clouds from Stephens 1978Version 3 has option to account for terrain slope and shadowing effects on the surface solar fluxSimple downward integration of solar flux, which accounts for:Clear air scatteringWater vapor absorption [Lacis and Hansen, 1974]Cloud albedo and absorption
4 Goddard Scheme ra_sw_physics = 2 Based on Chou and Suarez 1994Includes 11 spectral bandsDifferent climatological profiles available for numerous ozone optionsConsiders both diffuse and direct solar radiation in 2- stream approach, accounts for scattering and reflection
5 RRTMG Scheme ra_sw_physics = 4 Uses MCICA [Monte Carlo Independent Column Approximation] method of random cloud overlap – statistical method to resolve sub-grid scale cloud variabilityFiner 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.
6 Temperature ----- Meeting Notes (11/29/10 10:20) ----- No significant differences, perhaps some reducting in warm layer near surface in schemes 1 and 2 around sunrise-ish.
7 Relative Humidity ----- Meeting Notes (11/29/10 10:20) ----- Some drying at mid levels in Option 4 near the end of the run.
8 Zonal Winds ----- Meeting Notes (11/29/10 10:27) ----- Odd - weak winds thoughout the plot, especially aloft.
27 Significant Variations and Conclusions Goddard Scheme (ra_sw_physics=2) initialized differently and gave the most extreme valuesMost 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 heatingSurface 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
28 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.