MERCATOR OCEAN JOURNA:
SEPTEMBER 2021
1. The IBI-MFC ocean physical analysis/forecast/
reanalysis component:
The IBI NRT PHY forecast system (Sotillo et al., 2020)
is based on a 1/36° (-2.5 km) NEMO model application
continuously upgraded, since its first implementation
during MyOcean era (Maraldi et al., 2013). The IBI model
set-up was coded (at the start of Copernicus 1) in NEMO3.4
and it has then been upgraded to NEMO3.6. A more recent
NEMO4.x release code will be implemented (within the
H2020 IMMERSE Project [2021], where a future IBI product
demonstrator at 1/108° resolution is under development).
The atmospheric forcing has been progressively upgraded
from ECMWF 1/8° 3-hourly data to ECMWFIFS 1/12° hourly
data. Tidal forcing was also updated, including the loading
tide effect. Freshwater contribution from land is considered
in the model set-up, including river discharges from 33
main rivers and an extra coastal runoff contribution.
The IBI-MFC is working on enhancing this river freshwater
forcing; evaluating impacts of new river databases (such as
the one generated in the framework of the Copernicus Marine
Service Evolution [SE] Project Lambda) and testing the model
sensitivity with the IBI model operational set up (Sotillo et
al, 2021). In the last Copernicus Marine Service release (Dec
2020), an offline wave-current coupling (including effects
of Stokes drift & surface stress modification by waves) was
first Implemented in the IB! daily forecast cycle runs. The IB|
ocean circulation forecast system downscales the Copernicus
Marine Service Global solution (today, the IBI-PHY-NRT system
ıs nested into the GLO 1/12° daily updated physical solution).
Further details of downscaling effectiveness performed from
the Global solution through the IBI regional application are
available in Lorente et al., (2019).
The performance of different models, in terms of their eddy
properties and three-dimensional composite structures
was evaluated over the western Mediterranean Sea. See
the Copernicus Marine Service SE Project MEDSUB (2019).
It focused on assessing the mesoscale and sub-mesoscale
information iInclusion in different Copernicus Marine
Servic solutions. Mason et al., (2019) pointed out how
models that include data assimilation (GLO and MED, not
IBl at that time) approximate more precisely eddy property
distributions observed with contemporaneous altimetry
observations in the study area. One of the main IBI-MFC
objectives for Copernicus 1 was to include a DA scheme
in its physical component. An application of the MOI SAM2,
relying on a reduced order Kalman filter and based on SEEK
formulation (see Amo et al., 2020) was implemented. Since
April 2018, the IBI-MFC delivers regional physical analysis.
Before this data assimilation release, the IBI solution was
spectrally nudged to the Copernicus Marine Service global
system as a temporary solution to substitute the periodic
sequential forecast re-initialization. Figure 1 illustrates
the IBI performance improvement (gained in terms of
SST simulation) achieved along this path to include data
3ssimilation in the IBI-PHY-NRT system.
With respect to the IBI PHY MY products, the first 1/12°
reanalysis was run in 2015, covering the 2002-2011 period.
This first reanalysis was forced with ECMWF ERA-interim
and assimilated along-track SLA, maps of SST and in-situ
profiles (mostly from ARGO floats). In the last 6 years, two
major upgrades have been performed in this reanalysis
system, resulting in two new IBl long runs (and the related
:omplete IBI-PHY-MY product update in the Copernicus
Marine Service catalogue in 2018 and in December 2020).
Through these 2 IBI reanalyses releases, both the modeı
and the data assimilation scheme were upgraded along
with assimilated observations (i.e., including new altimetric
and SST observational products).
Likewise, the atmospheric forcing was updated, using the
new ECMWF ERAS5 in the last IBI reanalysis run. All these
-esulted in a continuous enhancement of IBI MY product
Juality (further details on the Copernicus Marine Service
Quality information document; Levier et al., 2021). Note that
the IBI reanalysis temporal coverage was extended back
to 1993, to cover the whole altimetric era. Finally, to point
aut that some efforts were done to evaluate differences
between the IBINRT and MY products delivered through the
zatalogue. Thus, periodic intercomparison with IB! physicaı
ocean products along the overlapping time periods have
been performed (see as example the analysis provided
by Aznar et al., 2017). The IBI-MFC aims to enhance its
product consistency, in particular between the NRT and MY
products, and to produce IBI reanalysis on a same mode
grid than IBI NRT forecast services
