CIRC: Continual Intercomparison of Radiation Codes

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The output (reference results) consists of the following:

  1. Pressure at atmospheric levels
  2. Upward broadband LW flux at atmospheric levels from LBLRTM
  3. Downward broadband LW flux at atmospheric levels from LBLRTM
  4. Broadband LW heating (cooling) rate of atmospheric layers from LBLRTM
  5. Central wavenumbers of 1 cm-1 bins (boxcar) for which LW spectral output from LBLRTM is provided
  6. Downward spectral LW flux at surface within 1 cm-1 bins (boxcar) from LBLRTM
  7. Upward spectral LW flux at TOA within 1 cm-1 bins (boxcar) from LBLRTM
  8. Downward broadband total SW flux at surface from CHARTS
  9. Downward broadband diffuse SW flux at surface from CHARTS
  10. Upward broadband SW flux at TOA from CHARTS
  11. Central wavenumbers of SW spectral output from CHARTS
  12. Downward total spectral (1cm-1) SW flux at surface from CHARTS calculated using delta-M scaling
  13. Downward true direct (no contributions from forward scattered radiation) horizontal spectral (1cm-1) SW flux at surface from CHARTS
  14. Upward spectral (1cm-1) SW flux at TOA from CHARTS

Tips and instructions on reading and using the output files

The output for each CIRC case consists of 3 files:

  1. LW_lblrtm_1cm-1_caseX.txt: Contains fluxes at the boundaries of the atmospheric column (downwelling surface and upwelling TOA) at 1 cm-1 resolution from LBLRTM.
  2. LW_lblrtm_bb_caseX.txt: Contains broadband flux and heating rate profiles from LBLRTM
  3. SW_charts_1cm-1_caseX.txt: Contains fluxes at the boundaries of the atmospheric column (downwelling surface and upwelling TOA) at 1 cm-1 resolution from CHARTS

The SW broadband fluxes are given at the beginning of the CHARTS 1 cm-1 output files. Note that the LW flux and heating rate profiles are inverted (values start at TOA and proceed to surface) in contrast to the input profiles where surface values are placed first.

Here is a sample FORTRAN code to read the contents of these files. The output files themselves can be downloaded from this page.

Description of reference observations and calculations

The longwave and shortwave surface irradiance measurements utilized for the CIRC SGP and NSA cases are 5-minute averages of the irradiance values provided by ARM Best Estimate Radiative Flux VAP. The 5-minute averaging window is centered at the time provided for each case.  The observed TOA irradiance values are from the temporally closest CERES measurement for Case 4 (NSA) and the temporally closest GOES broadband fluxes inferred from a radiance to flux and narrowband to broadband conversion algorithm, for cases 3 (SGP) and 7 (PYE). For the remaining SGP cases the weighted average of the two GOES-inferred fluxes bracketing the nominal BBHRP calculation time were used. The observed broadband irradiances can be found in the SW and LW summary tables.

Reference calculations
The reference radiative transfer calculations are performed with CHARTS v. 4.04 and LBLRTM v. 11.1 for the SW and LW part of the spectrum, respectively. The continuum model used was MT_CKD_2.0 and the line parameter file was AER_V_2.0. LBLRTM is run using 3 streams (i.e, 3 angles) while CHARTS is run using 16 streams with delta-M scaling and in our configuration provides fluxes only at the top and bottom boundary of the atmospheric column. The surface albedo is resolved at 1 cm-1 (the same as the one provided to the participants) and is linearly interpolated to the wavenumber of the calculation. The cloud optical properties (extinction coefficient, single-scattering albedo and asymmetry parameter) for the two cloudy cases are calculated from the retrieved layer water contents and effective radii using Mie theory and an assumed gamma droplet size distribution. Aerosols are treated similarly to BBHRP, i.e., the spectral aerosol optical thickness is obtained from the Angstrom relationship while g and SSA are spectrally invariant; a Henyey-Greenstein phase function is assumed. Output is averaged at 1 cm-1 intervals. In LBLRTM the cloud absorption optical thickness is also obtained from Mie calculations and cloud scattering is not accounted for (if your model accounts for LW scattering you may want to turn it off, if possible, for a more consistent comparison), as is any aerosol effect. The surface emissivity is set to unity across the LW spectrum .


For questions or problems reading/interpreting the output dataset please contact Lazaros Oreopoulos.

Last updated:
May 18, 2009
Web site contact: Lazaros Oreopoulos
Project contact: Lazaros Oreopoulos
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