MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
Tests with different turbulent schemes and albedo values 
were performed to eliminate a cold surface temperature 
bias. Some numerical schemes (e.g., using higher order 
numerics) and parameterizations were optimized to 
improve inflow and sea ice. Thereafter, vertical resolution 
sensitivity on salt inflows was studied. This investigation 
resulted in keeping the b6 vertical layers for the time being, 
and an increase in resolution in the top layer. 
Yalidation results from the final Nemo-Nordic 2.0 setup are 
seen in Figure 1, 2 and 3 for sea level variations assessed by 
tide gauge observations, the Baltic total ice extent estimated 
by ice charts, and salinity observations from moorings, 
respectively. Comparison of results between the old HBM and 
new NEMO systems shows improvements in stratification 
and the distribution of salinity in favour of the Nemo-Nordic 
2.0 setup. Additional validation results are avallable on 
the Copernicus Marine Service website. This new Nemo- 
Nordic 2.0 based system (Kärnä et al., 2021) has provided 
the operational forecast product since December 2020, and 
will further be used for a new reanalysis production to be 
started during 2021, planned to be released end of 2021 to 
Copernicus Marine Service users. 
The Baltic MFC wave analysis and forecast system is based 
on the WAM wave model (Komen et al., 1994). The first 
Baltic wave product, introduced into the CMEMS catalogue 
in 2017, used WAM cycle 4.5.4 and an upgrade to cycle 
4.6.2 was done in 2019 to enable coupling with the physicaı 
forecast system. The model domain covers the Baltic Sea 
with 1 nautical mile horizontal resolution with an oper 
boundary in the Skagerrak area. At the open boundary 
spectral-data from ECMWF'’s deterministic wave forecast 
are used. 
During the ice season, the ice conditions are accounted for 
by excluding grid points in the calculations that have an ice 
zoncentration over 30%. Ice concentrations at each model 
grid point have been evaluated based on FMI's ice charts 
‘available in the Copernicus Marine Service catalogue) 
until December 2020. Subsequently, the wave production 
system was updated to use hourly ice concentration from 
the Baltic MFC NEMO based physical forecast. Using the ice 
concentration forecast enables accounting for changing ice 
conditions during the 5 days forecast (Tuomi et al., 2019). 
Yowever, the accuracy of the ice forecast does not match 
-he ice charts. 
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= =\V201804 
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igure z: Computed total ice extent from the HBM (V201804) and the NEMO (V202012) systems based on ice chart observations for a 2 year 
period. 
Northern Baltic Sea shorelines display an iIrregular 
structure and, in places, covered with islands and islets 
Much smaller than the model grid size. To account for 
the effect this archipelago has on the attenuation of 
wave energy, a method to handle unresolved islands 
(e.g., Tolman, 2003) was implemented in the Baltic MFC 
WAM model code. This method reduces the wave energy 
propagated from one grid cell to the next one, according 
to the shadowing effect caused by unresolved islands 
The method improves the forecast quality and usability ir 
zoastal areas such as the Archipelago Sea, between the 
Baltic Proper and Gulf of Bothnia. For more information 
see description in Le Traon et al., (2017)