A fully coupled Mediterranean regional climate system model: design and evaluation of the ocean component for the 1980–2012 period

Abstract

A fully coupled regional climate system model (CNRM-RCSM4) dedicated to the Mediterranean region is described and evaluated using a multidecadal hindcast simulation (1980–2012) driven by global atmosphere and ocean reanalysis. CNRM-RCSM4 includes the regional representation of the atmosphere (ALADIN-Climate model), land surface (ISBA model), rivers (TRIP model) and the ocean (NEMOMED8 model), with a daily coupling by the OASIS coupler. This model aims to reproduce the regional climate system with as few constraints as possible: there is no surface salinity, temperature relaxation, or flux correction; the Black Sea budget is parameterised and river runoffs (except for the Nile) are fully coupled. The atmospheric component of CNRM-RCSM4 is evaluated in a companion paper; here, we focus on the air–sea fluxes, river discharges, surface ocean characteristics, deep water formation phenomena and the Mediterranean thermohaline circulation. Long-term stability, mean seasonal cycle, interannual variability and decadal trends are evaluated using basin-scale climatologies and in-situ measurements when available. We demonstrate that the simulation shows overall good behaviour in agreement with state-of-the-art Mediterranean RCSMs. An overestimation of the shortwave radiation and latent heat loss as well as a cold Sea Surface Temperature (SST) bias and a slight trend in the bottom layers are the primary current deficiencies. Further, CNRM-RCSM4 shows high skill in reproducing the interannual to decadal variability for air–sea fluxes, river runoffs, sea surface temperature and salinity as well as open-sea deep convection, including a realistic simulation of the Eastern Mediterranean Transient. We conclude that CNRM-RCSM4 is a mature modelling tool allowing the climate variability of the Mediterranean regional climate system to be studied and understood. It is used in hindcast and scenario modes in the HyMeX and Med-CORDEX programs.

• Mediterranean Sea
• regional climate system model
• air-sea fluxes
• hindcast simulation
• interannual variability

Acknowledgements

This work is a contribution to the HyMeX program (HYdrological cycle in the Mediterranean EXperiment) through INSU-MISTRALS support and the Med-CORDEX initiative (COordinated Regional climate Downscaling EXperiment – Mediterranean region). This research has received funding from the French National Research Agency (ANR) project REMEMBER (contract ANR-12-SENV-001) and from the European Commission as part of its 7 ^th Framework Program (CLIM-RUN, contract FP7-ENV-2010-265192).

The model version presented here is used in the projects FP7 IMPACT2C (grant 282746) and ANR ASICS-MED (contract ANR-12-BS06-0003). The outputs of the simulation described in this work can be downloaded from the Med-CORDEX database (www.medcordex.eu). The NEMOVAR-COMBINE reanalysis was produced under the FP7 COMBINE project (Grant Agreement number 226520).

We thank Marie-Noëlle Bouin and Sophie Belamari, who provided the LION and AZUR buoy datasets and participated in our discussions in this work of comparison, and Jonathan Beuvier for his corrections.

We thank W. Ludwig for the Mediterranean river datasets, E. Stanev for the Black Sea freshwater data, S. Marullo for his SST satellite products, M. Rixen for the 3D ocean climatology, B. Rossow and A. Romanou for the ISCCP data, P. Stackhouse for the SRB data, L. Yu for the OAFLUX data, S. Josey for the NOCS data and H. Kontoyiannis for the densities at the Antikithera, Kassos and Karpathos straits.

The altimeter products were produced by SSALTO/DUACS and distributed by Aviso, with support from CNES (http://www.aviso.oceanobs.com/duacs/).