MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
1.3 OMEGA3D 
A new MY product called OMEGA3D developed by CNR is 
available online since April 2020. It provides observation- 
based 3D quasi-geostrophic vertical and horizontal ocean 
currents over 75 levels from the surface to 1500 m depth, at 
1/4° horizontal resolution, from January 1993 to December 
2018. Current velocities are obtained by solving a Q-vector 
formulation of the Omega equation, including diabatic 
forcing terms (Buongiorno Nardelli, 2020). This product is 
wre MFCASD vertical velocity (SO m) 
based on a combination of different fields: temperature, 
salinity and geostrophic currents provided by ARMOR3D 
and ERA-Interim surface fluxes. Vertical velocities are 
now included in the list of parameters available through 
Zopernicus Marine Service catalogue. 
An illustration of OMEGA3D quasi-geostrophic verticaı 
currents at 50 m is given in Figure 2. It shows vertica 
axchanges about 10 meters per day associated with the 
Sulf Stream mesoscale activities but also the effect of 
Hurricane Florence. 
"Tan 
Vertical exchanges in 
response to Florence 
Hurricane 
gure 4: OM 
3osition (richt) 
GA3D vertical velocity at 50m depth (in m/day) for the 12/09/2018 (left) and MODIS Aqua image illustrating Florence Hurricane 
1.4 Surface and near-surface current 
(Copernicus-Globcurrent) 
The geostrophic currents are calculated through the 
Jeostrophic approximation applied to the sum of altimeter 
sea level anomalies (SLA) and a mean dynamic topography 
{MDT), both coming from Copernicus Marine Service Sea 
Level TAC. Ekman currents are computed at two depths 
(0m and 15m) applying an empirical Ekman model updatec 
from Rio et al., (2014) to ECMWF wind stress fields. 
Parameters of the empirical Ekman model are computed 
using in situ observations from Argo drifts at the surface 
and SVP-type drifters at 15 m. 
IWO versions of the product have been successively released. 
For its 1% publication in July 2018, geostrophic currents were 
from DUACS DT-2018 and Ekman currents were computed 
using ERAinterim wind stress fields. For its 2" publication in 
December 2019, both MY and NRT products were improved 
using new upstream fields such as the CNES-CLS18 mean 
dynamic topography and wind stress fields from ERA5 
which is the latest climate atmospheric reanalysis produced 
by ECMWF. The 2" publication also used an estimation of 
the ocean stratification coming from the mixed-layer depth 
of ARMOR3D in a new configuration of the empirical Ekman 
model. The MY timeseries have been extended twice a year, 
as soon as upstream fields were available. It currently 
zovers the 1993 — Mav 2020 period. 
It is well recognized that surface currents in the ocean are 
aot the simple addition of different current components. 
Although, a simple approximation of ocean currents can 
be made by combining geostrophic currents (derived 
from altimeter Absolute Dynamic Topography fields) with 
an estimate of the Ekman response to wind forcing. CLS 
has been producing for internal use, global fields of such 
combined geostrophic+Ekman currents which have been 
continuously improved (Rio et al., 2014). In 2014, ESA 
funded the GlobCurrent project (2014-2017) under the 
Data User Element program in which global combined 
surface and near-surface ocean current based on CLS 
work have been provided in delayed-time and in NRT. In 
2018, Copernicus Marine Service took over the production 
and distribution of this product now called Copernicus- 
Globcurrent with a first version online since July 2018. 
Copernicus-Globcurrent product consists in total velocity 
fields (zonal and meridional) at 0 m and 15 m depth, at& h 
frequency in NRT and at 3 h frequency for MY timeseries. 
Daily and monthly means are also available.