Radiative transfer schemes

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

• The "legacy" (oldest) radiative scheme is 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. This is the radiative code that was used in LMDZ4. It was written by Foucart and Morcrette at ECMWF. The description of the solar part of the spectrum, in particular, is not satisfying.
• RRTM, selected with iflag_rrtm=1 (and requiring that NSW=6), which is available if makelmdz has been run 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 makelmdz has been run 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.
• Tripleclouds : trois colonnes par maille : ciel clair, nuageux compact, nuageux intermédiaire. Le plus proche de RRTM.
• Tripleclouds 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 (Rapid Radiative Transfer Model for GCMs). 16 longwave bands and 14 shortwave bands.
• ECCKD (ECMWF correlated k-distribution scheme)