Diapositive 1

1
Assessment and validation of the new multivariate
Mercator high resolution forecasting system
PSY2v2 Operational since October 2005
Contact jean-michel.lellouche_at_mercator-ocean.fr
Jean-Michel Lellouche, Mounir Benkiran, Laurence
Crosnier and Eric Greiner
Mercator-Océan Parc Technologique du Canal,
8-10 rue Hermès, 31526 Ramonville Saint Agne,
France
The Mercator Ocean Monitoring and Forecasting
System is routinely operated in real-time in
Toulouse by the Mercator Project since early
2001, and has been regularly upgraded through
three prototypes of increasing complexity (PSY1,
PSY2 and PSY3), expanding the geographical
coverage from regional to global, improving
models and assimilation schemes. Since January
8th 2003, the high resolution system PSY2v1
provides, in an operational mode, oceanic
forecasts every week (http//www.mercator.com.fr).
In this first version of PSY2, only the Sea
Level Anomaly (SLA) from altimeter measurements
along tracks is assimilated with a univariate
mode and the 2D increments of SLA are converted
into 3D increments of U, V, S, T and TKE using an
algorithm based on the lifting-lowering
method. The new prototype PSY2v2 assimilates, in
a fully multivariate way, SLA from JASON-1,
ENVISAT and GFO, REYNOLDS SST, REYNAUD SSS
climatology and T/S vertical profiles provided by
the CORIOLIS centre, after a catch up to real
time by January 1th 2003 from the climatology
MEDATLAS2 in the Mediterranean basin and REYNAUD
in the Atlantic. The ocean model configurations
retained by the Mercator project are based on the
OPA ocean circulation model. We focus here on the
configuration designed to simulate the Atlantic
and Mediterranean oceans with a very high
horizontal resolution (5 to 7 km) and 43 levels
on the vertical. The assimilation method is based
on the Reduced-Order Optimal Interpolation
algorithm and uses 1D vertical multivariate EOFs
to extract statistically-coherent information
from the observations.
SLA (year 2004)
Temperature profiles (year 2004)

• The first figure concerns the number of
  temperature profiles entered into the system
  versus time and depth. This number becomes
  particularly important in the second half of the
  year ( 500 profiles).
• The second figure shows the variations of the
  mean value of the misfits (differences between
  the observation and model forecast), which is
  weak during the whole year.
• The RMS value of the misfit is plotted on the
  third figure and proves to be small, with a
  maximum at the thermocline depth.
• Satellite altimetry is used to constrain weekly
  the geostrophic currents. The data number
  exhibits the data availability in real-time. The
  RMS of the misfits reach 8 cm and represents 75
  of the data variability.

Origin, separation and westward progression of
an anticyclonic eddy in the Gulf of Mexico
The Subtropical UnderWater (Zonal section of
salinity at 26N)
Mediterranean Waters
One of the main problems with univariate
prototypes is the representation of Mediterranean
waters, mainly its vertical position near 1000m.
The figure shows the salinity at 1000m (April
2004) from PSY2v2 simulation. We see salty water
which corresponds to the characteristics of
Mediterranean waters (salinity close to 36.3
psu), with meddies formation and propagation.
6 weeks (from 25 July 2004 to 4 September 2004)
Chlorophyll-A (MODIS-CATSAT)
SSH (PSY2v2)
We can see here a comparison of the model SSH
with Chlorophyll-A concentration which is not
assimilated by the system, during a cycle of 6
weeks from July to September 2004 The
generation and evolution of the loop current
eddies in the Gulf of Mexico is represented in a
very realistic way by the system. From week1 to
week6 (from top to bottom), we can follow the
generation, the separation and the westward
translation of the eddy, which happen in the
model in phase with observations. Warm eddies are
characterized by a weak chlorophyll concentration
An other example showing the impact of T/S
vertical profiles assimilation is the good
representation of waters called Subtropical
Underwater. A WOCE zonal salinity section at 26N
shows the Subtropical Underwater (STUW), with
salinity characteristics ranging from 36.6 to
36.9psu, centred at around 200m depth in the
western Atlantic basin from 80W to 50W. The
same salinity section in the previous
univariate/monodata system does not display the
STUW salinity characteristics, whereas the PSY2v2
system does.