Ilicak, Mehmet

The Mediterranean and Black Sea operational forecasting systems are developed and continuously improved in the context of the Copernicus Marine Environment and Monitoring Service (CMEMS). The two systems operationally produce analyses and 10-days forecasts of the main physical parameters (Temperature, Salinity, Sea Level, Currents, Mixed Layer Depth) with a resolution of about 4.5km in the horizontal over 141 vertical levels in the Mediterranean Sea, and about 3km in the horizontal over 31 vertical levels in the Black Sea. The hydrodynamic numerical solutions are based on the NEMO (Nucleus for European Modelling of the Ocean) model coupled to a 3D variational data assimilation method (3DVAR) able to assimilate in-situ temperature and salinity profiles, satellite along-track sea level anomaly and sea surface temperature (in the Mediterranean Sea a nudging to satellite SST-L4 dataset is provided). The Mediterranean system is also 2-way online coupled with the WW3 (WaveWatch3) wave model to better represent the surface drag coefficient. The two systems are forced by 1/8o degree ECMWF (European Centre for Medium-range Weather Forecasts) atmospheric fields. The systems are validated in near real time and the quality of the products is monitored through regional websites (http://medfs.cmcc.it/ and http://bsfs.cmcc.it/) showing the analysis and forecast field maps at different depths (in case of 3D variables) as well as a weekly validation of model analysis compared with available observations. The focus of this work is to present the latest modelling system upgrades and the related improvements achieved by showing the model skill assessment including comparison with in-situ and satellite observational datasets.

We present an analysis of annual and seasonal mean characteristics of the Indian Ocean circulation and water masses from 16 global ocean-sea-ice model simulations that follow the Coordinated Ocean-ice Reference Experiments (CORE) interannual protocol (CORE-II). All simulations show a similar large-scale tropical current system, but with differences in the Equatorial Undercurrent. Most CORE-II models simulate the structure of the Cross Equatorial Cell (CEC) in the Indian Ocean. We uncover a previously unidentified secondary pathway of northward cross-equatorial transport along 75 °E, thus complementing the pathway near the Somali Coast. This secondary pathway is most prominent in the models which represent topography realistically, thus suggesting a need for realistic bathymetry in climate models. When probing the water mass structure in the upper ocean, we find that the salinity profiles are closer to observations in geopotential (level) models than in isopycnal models. More generally, we find that biases are model dependent, thus suggesting a grouping into model lineage, formulation of the surface boundary, vertical coordinate and surface salinity restoring. Refinement in model horizontal resolution (one degree versus ¼ degree) does not significantly improve simulations, though there are some marginal improvements in the salinity and barrier layer results. The results in turn suggest that a focus on improving physical parameterizations (e.g. boundary layer processes) may offer more near-term advances in Indian Ocean simulations than refined grid resolution.

We present a new surface-atmospheric dataset for driving ocean–sea-ice models based on Japanese 55-year atmospheric reanalysis (JRA-55), referred to here as JRA55-do. The JRA55-do dataset aims to replace the CORE interannual forcing version 2 (hereafter called the CORE dataset), which is currently used in the framework of the Coordinated Ocean-ice Reference Experiments (COREs) and the Ocean Model Intercomparison Project (OMIP). A major improvement in JRA55-do is the refined horizontal grid spacing (∼ 55 km) and temporal interval (3 hr). The data production method for JRA55-do essentially follows that of the CORE dataset, whereby the surface fields from an atmospheric reanalysis are adjusted relative to reference datasets. To improve the adjustment method, we use high-quality products derived from satellites and from several other atmospheric reanalysis projects, as well as feedback on the CORE dataset from the ocean modelling community. Notably, the surface air temperature and specific humidity are adjusted using multi-reanalysis ensemble means. In JRA55-do, the downwelling radiative fluxes and precipitation, which are affected by an ambiguous cloud parameterisation employed in the atmospheric model used for the reanalysis, are based on the reanalysis products. This approach represents a notable change from the CORE dataset, which imported independent observational products. Consequently, the JRA55-do dataset is more self-contained than the CORE dataset, and thus can be continually updated in near real-time. The JRA55-do dataset extends from 1958 to the present, with updates expected at least annually. This paper details the adjustments to the original JRA-55 fields, the scientific rationale for these adjustments, and the evaluation of JRA55-do. The adjustments successfully corrected the biases in the original JRA-55 fields. The globally averaged features are similar between the JRA55-do and CORE datasets, implying that JRA55-do can suitably replace the CORE dataset for use in driving global ocean–sea-ice models.