MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
The need to understand and validate the impact of the 
ıncreased resolution has required an update of validation 
and verification techniques. High-resolution observations 
like gliders and high frequency (HF) radar have been 
Jsed for assessing this new product. The NWS-MFC has 
pulled through the neighbourhood techniques developed 
by the Copernicus Marine Service SE Phase 2 HiVE project 
(Crocker et al., 2020) to assess the impact of the resolution 
on forecast fields. This methodology has also been used 
very recently to compare NWS products with other 
Copernicus Marine Service’s models, for regions where 
they overlap. 
In December 2020, the PHY and WAV forecast models have 
been coupled, thanks to the work done during CMEMS SE 
Dhase 1 projects Nemo2wave and OWAIRS (Lewis et al., 
2019). The PHY-WAV coupled system is coupled at hourly 
frequency and has three wave-currents interactions: 
- modification of surface stress by wave growth and 
dissipation, 
- Stokes-Coriolis forcing, 
wave-height-dependent ocean surface roughness. 
A study investigated the impact of the coupling on the 
sub-surface dynamics during storm events, assessing 
the accuracy of the currents against drifters (Bruciaferri 
et al., 2021). It demonstrated that the coupling improves 
the accuracy of the surface dynamics, with larger 
improvementson shelf (8%) than in the deep part of the NWS 
Forecast and Reanalysis number of users 
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domain (4%). Figure 5 shows an example of Lagrangian 
particles forced by the coupled and uncoupled version of 
the model, compared with drifter trajectories. The choice to 
focus on the horizontal current validation was user driven, 
since the most downloaded forecast variable is the hourly 
currents at 1.5 km resolution. Validation of ocean currents 
is challenging due to lack of high-resolution observations 
in this area. This R&D work was undertaken using drifters 
and HF Radar and will lead the way for future validation 
and verification processes for ocean currents. 
“he tidal variation In the shoreline is appreciable in some 
regions with a model resolution of 1.5 km. A significant 
part of the coastal shelf area is very shallow and tidally 
jdominated. NEMO version 3.6 does not allow grid cells to wet 
and dry so a minimum depth (10 m) was imposed for wet 
zells in shelf areas, where the tidal range is several metres. 
This choice decreases the reliability of the model in very 
shallow coastal areas. The processes of wetting and drying 
have been implemented on NEMO version 4 and tested in 
the NWS configuration (0’Dea et al., 2020). Including these 
processes in the PHY model will improve the tidal signa 
and the quality of the product in coastal area. NWS systems 
will be updated to NEMO version 4 with wetting and drying 
ın a future version, removing the imposition of a minimum 
depth of 10 m. For the coupled PHY-WAV system this will 
also Iinvolve running WAVEWATCH Ill with time-varying 
water levels provided from the PHY model. 
Forecast products users 
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ıure &: Users statistics for groups of NWS products. The number of distinect users for each class of product are plotted.