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

2. MOTIVATIONS test the fast  -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  m –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  -two stream radiation code with treatement of partial cloudiness –optical properties of clouds and gases parameterized over 8 wide spectral intervals from VIS (0.2  m) to FIR (104.5  m) based on AFGL ’84 database

5. COMPARISON SETTINGS Surface type: Lambertian Gaseous absorption: CO 2, H 2 O, O 3, N 2 O, O 2, CO, CH 4 for both models. RTX consider also trace gases as CFCs (F11, F12, CCl4), NO, NO 2, SO 2, N 2. Monocromatic RTX fluxes grouped in GRAALS bands. Spectroscopic database of RTX extend from FIR to 0.4  m. In solar region the comparison covers only 2 of the 3 GRAALS solar bands (i.e. the VIS range 0.2-0.7  m 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)

8. Solar spectrum in GRAALS is all distributed from 0.2 to 4.5  m CO 2 CO 2, H 2 O O3O3 H2OH2O

9. Sun zenith angle=60°

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

11. Contribute due to FIR H 2 O band (20-104  m) Contribute due to CO 2 band (12-20  m) Contribute due to O 3 band (9-10  m)

12. VIS and UV O 3 band: work in progress...

13. –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/m 3, r e =9.3  m medium-level water cloud –672-633 hPa (500m thick); LWC=0.129 g/m 3, r e =5.2  m high-level cloud –266-247 hPa (500m thick); LWC=0.013 g/m 3, r e =4.1  m SCENARIO-2: CLOUDY

14. Sun zenith angle=60°

21. 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)