COMPARISON OF RITTER-GELEYN RADIATON CODE TO LBL MODEL RTX

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COMPARISON OF RITTER-GELEYN RADIATON CODE TO LBL
MODEL RTX
7th COSMO General Meeting 20-23 september 2005,
Zurich (CH)

• PRELIMINARY RESULTS

Alessio Bozzo ADGB Phys. dep. Univ. of Bologna
ARPA-SIM
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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

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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

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MODELS OVERVIEWGRAALS

• 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

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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)

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SCENARIO-1 CLEAR

• standard tropical profile
• solar zenith angles 0, 45, 60

H2O mixing ratio (g/kg)
O3 mixing ratio (g/kg)
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Solar spectrum in GRAALS is all distributed from
0.2 to 4.5mm
O3
H2O
CO2
CO2,H2O
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Sun zenith angle60
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TOA and SURFACE NET Fluxes RTX-GRAALS ()
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Contribute due to O3 band (9-10mm)
Contribute due to FIR H2O band (20-104mm)
Contribute due to CO2 band (12-20mm)
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VIS and UV O3 band work in progress...
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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) LWC0.5 g/m3, re9.3mm
• medium-level water cloud
• 672-633 hPa (500m thick) LWC0.129 g/m3,
  re5.2mm
• high-level cloud
• 266-247 hPa (500m thick) LWC0.013 g/m3, re4.1mm

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Sun zenith angle60
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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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