COMPARISON OF RITTER-GELEYN RADIATON CODE

TO LBL MODEL RTXPRELIMINARY RESULTS

Alessio Bozzo – ADGB Phys. dep. Univ. of Bologna

ARPA-SIM

7th COSMO General Meeting

20-23 september 2005, Zurich (CH)

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

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

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 (0.2m) to FIR (104.5m) based on AFGL ’84 database

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 0.4m. In solar region the comparison covers only 2 of the 3 GRAALS solar bands (i.e. the VIS range 0.2-0.7m is not taken into account for now)

SCENARIO-1: CLEAR

standard tropical profile

solar zenith angles: 0°, 45°, 60°

H2O mixing ratio (g/kg)

O3 mixing ratio (g/kg)

Solar spectrum in GRAALS is all

distributed from 0.2 to 4.5m

CO2

CO2,H2O

O3

H2O

Sun zenith angle=60°

TOA and SURFACE NET Fluxes RTX-GRAALS (%)

TOA FLUXES

SURFACE FLUXES

Solar spectrum (0.7-4.6um)

Thermal spectrum (4.6-104.5um)

UP- FLUX -12.3% -4.6%

DOWN - FLUX -4.4%

Solar spectrum (0.7-4.6um)

Thermal spectrum (4.6-104.5um)

UP - FLUX 12.9% -0.8%

DOWN - FLUX -8.8% 0.7%

Contribute due to FIR H2O band (20-104m)

Contribute due to CO2 band (12-20m)

Contribute due to O3 band (9-10m)

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

– 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=9.3m

• medium-level water cloud– 672-633 hPa (500m thick); LWC=0.129 g/m3,

re=5.2m

• high-level cloud– 266-247 hPa (500m thick); LWC=0.013 g/m3,

re=4.1m

SCENARIO-2: CLOUDY

Sun zenith angle=60°

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)