RTE+RRTMGP Shortwave/Longwave Radiation Scheme

Description

RTE+RRTMGP is a set of codes for computing radiative fluxes in planetary atmospheres.

RRTMGP uses a k-distribution to provide an optical description (absorption and possibly Rayleigh optical depth) of the gaseous atmosphere, along with the relevant source functions, on a pre-determined spectral grid given temperatures, pressures, and gas concentration. The k-distribution currently distributed with this package is applicable to the Earth's atmosphere under present-day, pre-industrial, and 4xCO2 conditions.

RTE computes fluxes given spectrally-resolved optical descriptions and source functions. The fluxes are normally summarized or reduced via a user extensible class.

Clear-sky Optical Properties

The RRTMGP LW algorithm contains 128 unevenly distributed g-points (quadrature points) in 16 broad spectral bands, while the SW algorithm includes 112 g-points in 14 bands. In addition to the major atmospheric absorbing gases of ozone, water vapor, and carbon dioxide, the algorithm also includes various minor absorbing species such as methane, nitrous oxide, oxygen, and in the longwave up to four types of halocarbons (CFCs).

Aerosol Optical Properties

Aerosol optical properties for the RRTMGP bands are computed externally and provided to the radiation and incremented onto the gaseous optics. This is identical to how the aerosol optics are included within RRTMG. There are no internal assumptions on aerosol properties within the radiation scheme.

Cloud Optical Properties

Cloud optical properties are computed as a function of effective radius for the RRTMGP bands. Based on Mie calculations for liquid and results from Yang et al. 2013 [204] for ice with variable surface roughness.

To represent statistically the unresolved subgrid cloud variability when dealing multi layered clouds, a Monte-Carlo Independent Column Approximation (McICA) method is used prior to calling the RTE. Several cloud overlap methods, including maximum-random, exponential, and exponential-random are available in both LW and SW radiation calculations. (Unlike RRTMG, in RRTMGP the subgrid sampling step is not within the spectral loop, but rather happens outside of the RTE.)

fields from model outputs ( \(W m^{-2}\))

• At surface total sky
  • DLWRFsfc: Downward LW
  • DSWRFsfc: Downward SW
  • ULWRFsfc: Upward LW
  • USWRFsfc: Upward SW
  • NBDSFsfc: Near IR beam downward
  • NDDSFsfc: Near IR diffuse downward
  • VBDSFsfc: UV+Visible beam downward
  • VDDSFsfc: UV+Visible diffuse downward
  • DUVBsfc: UV-B downward flux
• At surface clear sky
  • CSDLFsfc: Downward LW
  • CSDSFsfc: Downward SW
  • CSULFsfc: Upward LW
  • CSDLFsfc: Downward LW
  • CSUSFsfc: Upward sw
  • CDUVBsfc: UV-B downward flux
• At TOA total sky
  • DSWRFtoa: Downward SW
  • ULWRFtoa: Upward LW
  • USWRFtoa: Upward SW
• At TOA clear sky:
  • CSULFtoa: Upward LW
  • CSUSFtoa: Upward SW

Intraphysics Communication

• GFS RRTMGP pre-processing used, for both Longwave and Shortwave: arg_table_GFS_rrtmgp_pre_run
• GFS surface-to-RRTMGP interface: arg_table_GFS_radiation_surface_run
• GFS RRTMGP cloud microphysics interface: arg_table_GFS_rrtmgp_cloud_mp_run
• GFS RRTMGP cloud overlap interface: arg_table_GFS_rrtmgp_cloud_overlap_run
• GFS cloud diagnostics: arg_table_GFS_cloud_diagnostics_run
• GFS RRTMGP aerosol interface: Argument Table
• GFS RRTMGP-Longwave radiation driver: Argument Table
• GFS RRTMGP-Shortwave radiation driver: Argument Table
• GFS RRTMGP post-processing, for both Longwave and Shortwave: arg_table_GFS_rrtmgp_post_run