Radiative transfer schemes

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

• the "legacy" (oldest) radiative scheme: always available. 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