MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
1.3 Med-MFC Waves Systems 
The evolution of the Med-MFC NRT wave component 
‚Med-waves) is shown in Figure 1. First released in 2017, 
it provided (short term) wave forecasts and simulations 
for the Mediterranean Sea on a daily basis (i.e., 5 days). It 
had a 1/24° horizontal resolution, 32 frequency bins and 
24 equally spaced directional bins for the discretization of 
the wave spectrum solved by the wave model (Ravdas et 
al., 2018). The Med-waves set-up included a coarse grid 
domain with a resolution of 1/6° covering the North Atlantic 
Ocean. It was developed and implemented using a state- 
of-the-art third-generation wave model, WAM Cycle 4.5.4. 
In March 2018, the system was upgraded by incorporating 
a data assimilation component to leverage available along- 
track Significant Wave Height (SWH) satellite observations 
gathered from Sentinel-3A and Jason-3 (Sea Level- 
TAC). The assimilation module was based on an optimal 
Interpolation of the total SWH retrieved by altimeters 
(Lionello et al., 1992). 
In 2019, the wave model upgraded to Cycle 4.6.2 and 
the forecast was extended up to 10 days. Additionally, 
modifications were introduced to the wave age parameter 
‚ZALP = 0.011) whitecapping dissipation coefficients, 
while a limitation at high frequencies matching the latest 
ECMWF wave forecasting system Cy43r1 (ECMWF, 2016) 
was applied in order to reduce the wave steepness at 
very high wind speeds. The same year, new along track 
ınter-calibrated SWH observations from Cryosat-2 and 
Saral/Altika satellite missions were added to the data 
assimilation module while Sentinel-3b observations were 
added in 2020. 
The quality of the Med-Waves analysis and forecast system 
ver the period April 2017 —- April 2021 (release in 2021) 
Was continuously assessed over yearly reference periods 
(2014 reference period until the version released in Feb 
2018, 2016 until the release of April 2019 and Jul 2019- 
Jul 2020 for the latest versions of the system). It enablec 
the comparison between in situ observations from moorea 
wave buoys (INS-TAC) and satellite altimeter observations 
(merged altimeter SWH database setup at CERSAT - 
IFREMER and Wave-TAC). 
The overall quality of the system then showed annua 
scatter indexes (SI) equal to 24% for in situ and 15% for 
satellites SWH observations. The quality evolution of SWE 
and Mean Wave Period (MWP) components is shown ir 
Figure 4 separately for in situ and satellite observations. 
Since April 2017, a continuous improvement of the SW 
satellite observations’ quality is visible. When comparing 
Med-waves SWH with in situ observations a drop in 
normalized RMSD is evident in April 2018 while the quality 
remains almost unchanged afterwards. As for the MWP the 
normalized RMSD with respect to buoy observations shows 
a decreasing trend from October 2017 release until 202” 
Until 2020, the multi-year wave product consisted of a 
*3-year wave hindcast (2006 - 2019) produced using the 
2017 Med wave NRT system, forced by 6-hours operational 
analysis 10 m ECMWF winds and daily surface currents 
from Copernicus Marine Service physical reanalysis. Since 
2021, the multi-year wave product is a 27-year wave 
reanalysis for the period 1993 - 2019 (described in the 
following section).