Changes in the global upper ocean with new NEMOv4 features

New and updated physics and parameterizations implemented in the NEMO ocean model from version 4 onwards are tested in a global eddying ocean/sea ice configuration, specifically the GLOB16 system. Such configuration is at the base of the operational short-term Global Ocean Forecast System (GOFS) adopted at the Euro-Mediterranean Center on Climate Change (CMCC) and uses a nonuniform tripolar grid with 1/16° horizontal resolution (corresponding to 6.9 km at the Equator) and 98 vertical levels. We performed a set of short-term simulations forced by the ECMWF operational atmospheric fields at 1/10° spatial resolution.

Among all the recent functionalities of the NEMO model, this work focuses on the new features that could impact the ocean energy budget. The new formulation of tides, the parameterization of the mixing induced by breaking internal waves and the formulation of the surface wave-induced mixing are selected. Test simulations are compared against a control run employing a set of metrics computed on the global domain and regional ocean sectors. Additionally, model results are evaluated against available satellite estimates to provide a first validation of the variability of upper ocean energy budget.

In the simulation in which the surface wave-induced mixing is included, external input forcings are needed to provide an accurate representation of the surface wave processes. Here, integrated wave parameters from WAVEWATCH III model feed the NEMO ocean model, in the forced mode.

Our analysis shows that all new ocean implementations impact global and regional patterns of sea surface salinity and sea surface height; conversely, only enhanced surface mixing affects the sea surface temperature and the mixed layer depth. However, all experiments showed the tendency to reduce the surface and basin-averaged ocean energy with updated mixing processes.