CNRM-RCSM6 : A regional climate system model, high-resolution, multi-component and fully-coupled.

Introduction and scientific choices

– Improve the CNRM-RCSM4 coupled model formerly used (Sevault et al. 2014) ;
– Follow the last version of the CNRM-CERFACS GCM, used for the CMIP6 intercomparison (Description, references) ;
– Follow the MedCORDEX recommendations for the inter-comparison ;
– Use up-to-date components as lateral boundary conditions (LBC), initial conditions and forcing.

Model components

ALADIN_Climate V6 (Daniel et al., 2019) : 12 km resolution, 91 levels, with interactive aerosols with TACTIC (Michou et al., 2015), SURFEX v8.0 externalised surface system (Voldoire et al., 2017), in which the ISBA-CTRIP land surface system and the FLake lake scheme (Le Moigne et al., 2016) are embedded ;
ISBA-CTRIP (Decharme et al., 2019) : floodplains, groundwater diffusive scheme, variable velocity, 50 km resolution ;
NEMOMED12 (Beuvier et al., 2012 for v3.2) : regional version of NEMOv3.6 (Madec et al., 2008), 6-8 km resolution ;
OASIS3-MCT (Craig et al., 2017) : 1-hr coupling frequency.

Domain

ALADIN-Climate land-sea mask and orography (in m) for the AAD12 domain, and NEMOMED12 bathymetry (in m). The drainage areas of the Black Sea (in black) and the Mediterranean Sea (in red) are contoured.

Set-up explanations:

The river runoffs computed by SURFEX are sent to the CTRIP model, while the river discharges at the river mouths are sent by CTRIP to the ocean model. Only the CTRIP cells within the Mediterranean and Black Sea drainage areas are considered ; for the Nile river basin, the runoff is prescribed using a 12-month climatology, as for CNRM-RCSM4. The NEMOMED12 ocean model does not include the Black Sea in its domain. The Black Sea is instead treated as a river, inducing a difference of salinity between the Aegean Sea and the Marmara Sea. In the coupled system, the river discharges from the Black Sea drainage area (58 river mouths in the CTRIP 0.5° grid) are summed with the Evaporation minus Precipitation (E-P) budget from SURFEX over the Black Sea. The 0.5° resolution of the CTRIP grid is coarser than those of atmosphere and ocean, and will be modified as soon as a finer resolution is available. Outside the NEMOMED12 domain in the Atlantic Ocean, the Baltic Sea and the Black Sea, an SST field must also be provided to the atmospheric model ; it usually comes from the same dataset as the lateral boundary conditions supplied to the regional atmospheric model.

References