MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
Temperature RMSD @ 10-30m Analysis & 3rd Day Forecast 
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MED-PHY 1/24 AN -—— MED-PHY 1/24 FC> 
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„igure 2: Timeseries of temperature Root Mean Square Difference (RMSD) between model and observations in a 10 to 30 meters layer fo! 
model analysis (solid line) and 3'“ day of forecast (dashed line). Red lines: 1/16° model; blue lines: 1/24° model resolution. Dashed areas 
represent the number of observations. 
An example is shown in Figure 2 presenting a timeseries 
of temperature Root Mean Square Difference (RMSD) 
between model and in situ observations averaged between 
10-30 meters. The skill in this layer is dominated by a 
seasonal cycle characterized by a larger error in the 
summer period due to the temperature stratification and 
a shallow thermocline. Both temperature model analysis 
and the 3 day forecast show a reducing error thanks to 
system improvements. 
The Physical Reanalysis system upgrades since 2015 were 
integrated in the new reanalysis timeseries delivered in 
2020 (Escudier et al., 2020). The main differences between 
the reanalysis produced since the beginning of the 
Copernicus Marine Service (Simoncelli et al., 2019) and the 
new one consist of: 
- increase of system resolution to 1/24° (ca 3.5 km) and 
141 vertical levels and improved bathymetry, 
- update of the hydrodynamic model to NEMO v3.6, 
increase of the river inputs (from 7 to 39), 
daily lateral open boundary conditions in the Atlantic 
derived from a global reanalysis (instead of monthly 
climatologies), 
use of ERA5 (instead of ERA-Interim) atmospheric 
forcing, 
update of the assimilation scheme and assimilation of 
a larger number of observations. 
The Physical Reanalysis presents an overall increased skill 
and a reduced RMSD for all variables and at all depths 
when compared to observations. Also, the representation 
of the mixed layer depth and deep convection events in 
areas of water mass formation is Improved compared to 
state-of-the-art climatology and literature (more details in 
(he product QUID). 
1.2 Med-MFC Biogeochemical Systems 
ı he Biogeochemical analysis and Forecast modelling system 
(MedBFM) features the coupled transport-biogeochemical 
model (0GSTM-BFM, Lazzari et al., 2010) and the 3DVarBio 
assimilation scheme (Teruzzi et al., 2014). The MedBFM is 
off-line coupled with MedFS over the whole Mediterranean 
Sea. The OGSTM transport model resolves advection, 
vertical diffusion and sinking terms of biogeochemica 
variables. The BFM model describes biogeochemical cycles 
af 4 chemical compounds (carbon, nitrogen, phosphorus 
and silicon) through the dissolved inorganic, living organic 
and non-living organic compartments. 
Irganic compartments include four phytoplankton 
Jroups (diatoms, flagellates, picophytoplankton and 
dinoflagellates), four heterotrophic zooplankton groups 
(carnivorous and omnivorous mesozooplankton, 
heterotrophic nanoflagellates and microzooplankton), one 
heterotrophic bacteria and four non-living compartments 
(labile, semilabile and refractory dissolved matter anc 
particulate matter). 
The 3DVarBio is a variational scheme that decomposes 
the background error covariance matrix using a sequence 
of operators (Dobricic and Pinardi, 2008). The covariance 
operators account separately for vertical, horizontal and 
biogeochemical covariance (Teruzzi et al., 2014). In 2015, 
the system assimilated surface Chlorophyll from satellite 
sensors for the open-sea area.