Radiative transfer schemes

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There are different radiative schemes that can be used in LMDZ:

  • the "legacy" (oldest) radiative scheme: available regardless of the makelmdz options used. May be selected using the iflag_rrtm=0 option in physiq.def. Note that this schemes also requires using 2 bands in the SW (Short Wave, i.e. visible wavelengths), i.e. setting NSW=2 in physiq.def
  • RRTM, selected with iflag_rrtm=1 (and requiring that NSW=6), which is available if the GCM has been compiled with the -rad rrtm option (see WhatIs: The makelmdz fcm script).
  • ECRAD (implementation is ongoing at the time of writing this) , selected with iflag_rrtm=2, which is available if the GCM has been compiled with the -rad ecrad option.

ECRad has three sub-options for the treatment of clouds:

  • McICA : Monte Carlo Independent Column Approximation. Assez rapide, comme si on faisait des sondages, on tire une dizaine de sous-colonnes.
  • triple cloud : trois colonnes par maille : ciel clair, nuageux compact, nuageux intermédiraire. Le plus proche de RRTM.
  • triple cloud avec Spartacus : effet 3D des nuages, multiplie par 5 le temps d'exécution du rayonnement.

ECRad also has two sub-options for the treatment of the gas phase:

  • RRTMG
  • ECCKD