Coastal Ocean Continuum in surface Topography Observations (COCTO) PIs: Nadia Ayoub and Pierre De Mey, LEGOS, Toulouse, France

Interested? Contacts: Pierre De Mey pierre.de-mey@legos.obs-mip.fr

Nadia Ayoub nadia-ayoub@legos.obs-mip.fr

Project participants

PIs: Nadia Ayoub & Pierre De Mey (LEGOS)

Co-Is: Guillaume Charria (IFREMER/LOPS, Brest) Marine Herrmann (IRD/LEGOS, Hanoi) Florent Lyard (CNRS/LEGOS) Patrick Marsaleix (CNRS/LA)

Other participants: Sylvain Ouillon (IRD/LEGOS) Florence Toublanc (LEGOS post-doc) Damien Allain (LEGOS engineer) Thomas Duhaut (LA engineer) Ozge Yelecki (LOPS PhD student) Sébatien Theetten (LOPS engineer) Frédéric Vandermeirsch (IFREMER/LOPS)

Science

Science drivers: • The estuary-shelf-coastal ocean continuum,

and in particular its small scales • Cross-shelf exchanges • Fine-scale dynamics on the shelf under the

influence of rivers, tides, the atmosphere and larger-scale dynamics

• Signature of fine-scale processes in sea-surface height

• Potential impact of SWOT measurements via data Assimilation, along with other data

Project structure: • Topic 1. Lower estuary dynamics :

• accuracy and realism assessment of 3D modelling of river flow, barotropic tides, storm surges and surface waves in lower estuaries

• 2D vs. 3D surface signature (sea level) of estuarine dynamical processes

• impact of extreme events (flooding, storms) • salinity and influence of mixing (plus possibly mud

flow effects) on the stratification • Hydrological modelling and T-UGOm comparisons

to be made in collaboration with B. Laignel and L. Chevalier (Univ. of Rouen) within their own SWOT project.

• Topic 2. Estuary to shelf transition • Topic 3. Small-scale processes on the shelf • Topic 4. Shelf break processes • Topic 5. Multiscale estimation approaches

Two target coastal regions

Methodology

• 2D and 3D fine-scale numerical modelling • Ensemble stochastic modelling • Satellite and in situ data, SWOT ocean simulator • Data assimilation by Ensemble Kalman filtering

Topic 2: Estuary to shelf transition

Bay of Biscay

Identification of coastal structures linked to plume-circulation interactions (SYMPHONIE circulation model) Calculation of the associated geostrophic currents

F. Toublanc et al., 2016

Daily mean sea surface elevation (m) August 2012

30 km 5 cm

Daily mean sea surface salinity (psu) Geostrophic currents calculated

from the ssh gradient (m/s)

Evaluation of the observability of these structures with the SWOT-ocean simulator (Gautier and Ubelmann, 2015)

Results from the SWOT simulator (m)

Topic 3: Small-scale processes on the shelf

• What will SWOT data bring to the description and understanding of the mid-shelf seasonal fronts in Sea Surface Height ?

• Intensity of mesoscale activity over the shelf (including the outer part) ?

• Other active processes with a potential signature on SSH (as internal waves for example) ?

Singularity exponents (28/03/2012 MODIS – Chl. conc.)

Illustration of small-scale patterns in the Bay of Biscay

Yelecki et al., LOPS, 2016

The Gulf of Tonkin case study

GoT grid, resolution 0.5 to 5 km

SCS grid, resolution 1 to 6 km

We intend to use the fast-sampling phase to evaluate the realism of the model and the

observability of small scale structures in the GoT and SCS in SWOT data.

2 SYMPHONIE grids currently used : one for the South China Sea (SCS), one for the Gulf of Tonkin (GoT)

0 1000 2000 3000 4000 Bathymetry

M. Herrmann and S. Ouillon, 2016

Possible applications in the Red River delta and CZ Goals: fluxes and fate of dissolved and particulate matter at the continent-ocean interface for the benefit of science (chemical cycles), health (contamination), management (sustainable development). Water Quality • Fate of dissolved and particulate matter during floods • Contamination in case of accidental chemical release Lagrangian studies • Sedimentation

in the Ha Long bay • Release of particles by

the Red River and from the northern basin with cement factories & mining activities

Extreme events • Storm surges, setup,

coastal erosion.