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COMPARISON OF RITTER-GELEYN RADIATON CODE TO LBL MODEL RTX

7th COSMO General Meeting 20-23 september 2005, Zurich (CH). COMPARISON OF RITTER-GELEYN RADIATON CODE TO LBL MODEL RTX. PRELIMINARY RESULTS. Alessio Bozzo – ADGB Phys. dep. Univ. of Bologna ARPA-SIM. MOTIVATIONS.

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COMPARISON OF RITTER-GELEYN RADIATON CODE TO LBL MODEL RTX

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  1. 7th COSMO General Meeting 20-23 september 2005, Zurich (CH) COMPARISON OF RITTER-GELEYN RADIATON CODE TO LBL MODEL RTX PRELIMINARY RESULTS Alessio Bozzo – ADGB Phys. dep. Univ. of Bologna ARPA-SIM

  2. MOTIVATIONS • test the fast d-two stream radiation code GRAALS with the LbL-multiple scattering model RTX • particolar attention is paid to the comparison between the treatement of gases, clouds and aerosols optical properties

  3. MODELS OVERVIEW: RTX • Benchmark model: RTX • LbL radiation code. • Spectroscopic database based on HITRAN2000 from FIR to 0.4 mm • cirrus cloud single scattering optical properties for spherical, hexagonal and aggregate crystals • “exact” multiple scattering computation of cloud and Rayleigh layers via adding-and-doubling method

  4. MODELS OVERVIEW:GRAALS • GRAALS (General Radiative Algorithm Adapted to Linear-type Solutions, Ritter/Geleyn 1991) • fast d-two stream radiation code with treatement of partial cloudiness • optical properties of clouds and gases parameterized over 8 wide spectral intervals from VIS (0.2mm) to FIR (104.5mm) based on AFGL ’84 database

  5. COMPARISON SETTINGS • Surface type: Lambertian • Gaseous absorption: CO2, H2O, O3, N2O, O2, CO, CH4 for both models. RTX consider also trace gases as CFCs (F11, F12, CCl4), NO, NO2, SO2, N2. • Monocromatic RTX fluxes grouped in GRAALS bands. Spectroscopic database of RTX extend from FIR to 0.4mm. In solar region the comparison covers only 2 of the 3 GRAALS solar bands (i.e. the VIS range 0.2-0.7mm is not taken into account for now)

  6. SCENARIO-1: CLEAR standard tropical profile solar zenith angles: 0°, 45°, 60° H2O mixing ratio (g/kg) O3 mixing ratio (g/kg)

  7. Solar spectrum in GRAALS is all distributed from 0.2 to 4.5mm O3 H2O CO2 CO2,H2O

  8. Sun zenith angle=60°

  9. TOA and SURFACE NET Fluxes RTX-GRAALS (%)

  10. Contribute due to O3 band (9-10mm) Contribute due to FIR H2O band (20-104mm) Contribute due to CO2 band (12-20mm)

  11. VIS and UV O3 band: work in progress...

  12. SCENARIO-2: CLOUDY • standard tropical profile with different cloud types at various heights (overcast homogeneus layers) • solar zenith angle 0°, 45°, 60° • low-level thick water cloud • 850-715hPa (1500m thick); LWC=0.5 g/m3, re=9.3mm • medium-level water cloud • 672-633 hPa (500m thick); LWC=0.129 g/m3, re=5.2mm • high-level cloud • 266-247 hPa (500m thick); LWC=0.013 g/m3, re=4.1mm

  13. Sun zenith angle=60°

  14. FURTHER WORK • Improve the parameterization of ice clouds with the most advanced particle shapes (aggregate, columns, hex. plates) (collaboration with UK Met Office) • Re-compute the gaseous optical properties using the last HITRAN2004 spectroscopic database (work in progress by F.Geleyn) • Compare the treatement of aerosol in GRAALS with the latest OPAC database in RTX (Hess, Koepke, and Schult, 1998)

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