Drift prediction at sea: the French operational system

The National Forecasting Centre of Météo-France provides met-ocean support and drift forecasts to assist authorities in charge of accidental marine pollution and search and rescue operations. The system is operated at Cedre's request in support of oil spill response operations and at the request of the Maritime Rescue Coordination Centres in support of search and rescue operations.
Drift forecasts are based on a drift system, called MOTHY. It has been operational since 1994 and was widely used during the Erika (December 1999), Prestige (November 2002) and Grande America (March 2019) crises in the Bay of Biscay. The system is activated about 20 times a week for actual spills or search and rescue operations. Searches for objects or individuals account for nearly three-quarters of the system's applications.

Wakashio

On July 25, 2020, the MV Wakashio hit a reef and ran aground off Pointe d'Esny, on the southeast coast of Mauritius. On the morning of August 6, oil leaked out of a fuel tank. Oil pumping operations were carried out. They were completed on August 12. On August 16, the ship broke in two. On August 19, the front part of the ship is towed about 20 kilometers from the coast. It sinks on August 24.

Grande America

The Grande America accident in the Bay of Biscay is the most significant event of 2019.

Due to a fire, the Grande America, which carried 365 containers and 2,000 vehicles, sank on 12 March 2019, 350 km off the French coast, with approximately 2,200 tonnes of bunker fuel on board. An unknown quantity of heavy fuel oil was released into the marine environment on the day the vessel sank, followed by 35 days of continuous leakage before the breaches in the hull were sealed by an underwater robot.
From 14 March, the Drift Committee, bringing together experts from Cedre, Météo-France, Ifremer and Shom, was responsible for providing the maritime Prefect with coherent and relevant information on oil slick drift on a daily basis. The MOTHY model was used daily during the aerial surveillance and recovery at sea period. It provided drift forecasts for oil slicks and containers up to 3 days in deterministic mode and up to 10 days in probabilistic mode. Long-term modelling of residual diffuse pollution was also carried out over several months, in particular to manage continuous leaks from the wreck.
Drift forecasts did not indicate any oil arrival at the coast. This allowed the authorities to organise the response at sea without mobilising resources ashore. No pollution has been observed on the coasts.

Sargassum

The Ministry for Ecological Transition has entrusted Meteo-France with the implementation of a service for detecting, monitoring and predicting the stranding of sargasso beds in the French West Indies and French Guiana. Up to 4 reports per day (one for each area: Northern Caribbean, Guadeloupe, Martinique and French Guiana) are prepared and sent to the national authorities in charge of sargasso management (DEAL). In this context, Meteo-France and Mercator Ocean International collaborate to calculate sargasso drift with the MOTHY model, and the Meteo-France Center for Space Meteorology ensures the detection of sargassum by satellite to produce the input data for the Meteo-France bulletins.

Ulysse/CSL Virginia

On October 7, 2018, the Tunisian ro-ro vessel Ulysse collided with the Cypriot container ship CSL Virginia at anchor off northern Corsica.
The spilled bunker oil could not be fully recovered by the French and Italian anti-pollution vessels due to unfavourable weather conditions. Pellets and highly viscous patties arrived on the beaches of the French Riviera on October 16, 2018.
The beaching dates and locations of the main slicks were perfectly predicted using the MOTHY drift model combined with the currents of the CMEMS MED-Currents system.

Météo-France commitments at national level

Météo-France participates in the fight against accidental pollution with the marine oil pollution response organizations, within the spill response plan POLMAR-MER. Météo-France is responsible for implementing pollutant drift forecasts in conjunction with Cedre, and providing the human expertise necessary for their interpretation.
In order to have coherent and relevant information on oil drift, observations and forecasts, the government has set up a Drift Committee since 2006. The Drift Committee is a technical committee bringing together experts in meteorology, oceanography, oil behaviour and pollution control from Cedre, Météo-France, Ifremer and Shom.
To ensure optimal reliability, Cedre and Météo-France set up a technical collaboration formalized by an agreement signed in 1996. Météo-France sends weather forecasts and pollutant drift forecasts to Cedre. In return, Cedre contributes to the improvement and validation of the model through its experiments and interventions on real pollution.
In order to respond as effectively as possible in the event of an accident, Cedre and Météo-France are constantly seeking to improve their crisis response capacity. They regularly participate in joint exercises to test this capability and evaluate system performance.

The system can also be used for specific studies.

International: MPERSS

The National Weather Services have the vocation to bring in real time Météo-oceanic information to various users, among whom organisations in charge of the control of pollution. They traditionally provide data and services to assist the operations in territorial waters. These services work then in close connection with the authorities in charge of the fight at sea. With an aim of ensuring a comparable service in quality in international waters, the WMO set up since 1994 the Marine Pollution Emergency Response Support System (MPERSS) for the high seas. It initially aims at setting up a coordinated system intended to provide weather and oceanographic information - when it is necessary and on request - for emergency interventions in the event of marine pollution outside territorial waters. The oceans and the seas are divided into areas of responsibility called MPI areas (Marine Pollution Incident), they correspond to METAERAS areas of the Global Maritime Distress and Safety System (GMDSS). On each of these areas, meteorological assistance is coordinated by an Area Meteorological and Oceanographic Co-ordinator (AMOC) who is a national meteorological service.

International: national meteorological services

As part of bilateral collaborations, MOTHY has been installed in various national meteorological services, including those in Bulgaria, Greece, Tunisia, Morocco and Senegal.

References

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NOOS-Drift

NOOS-Drift is a transnational multi-models ensemble system to assess and improve drift forecast accuracy in the European North West Continental Shelf Seas.
The NOOS-Drift service aims at providing end-users such as maritime authorities and coastguards stations from the countries bordering the European North West Continental Shelf Seas not only with drift trajectory forecasts but also with information on the accuracy of the forecast.
The service starts with three drift models: MOTHY, OpenDrift and Oserit and can be completed later by other models.

Key Characteristics of the MOTHY System

The MOTHY system developed by Météo-France is used on an operational basis to predict the drift of pollutants or floating objects on the ocean surface. The system includes local area hydrodynamic coastal ocean modelling and real-time atmospheric forcing from meteorological models.
It encompasses three distinct components:

• oil or any product that drift like a slick, including vegetable oil or a few chemicals.
• cargo containers
• search and rescue targets

Geophysical forcing data

Accurate and timely access to observed and predicted environmental data is of paramount importance for reliable drift predictions. In this regard, Météo-France employs state-of-the-art atmospheric and oceanic models, including:
For atmospheric modeling:

• The AROME limited area model covers the entire French coastline, with a 1.3 km grid around France and 2.5 km around French overseas territories ;
• The ARPEGE global model with variable mesh, centered on France, for forecasts over European seas and near Atlantic;
• The IFS global model of the European Centre for Medium-Range Weather Forecasts (ECMWF) has a resolution of 1/8°.

• Global ocean MERCATOR system with a resolution of 1/12°
• MERCATOR IBI system with a resolution of 1/36° covers the seas around mainland France
• MFS system with a resolution of 1/24° covers the entire Mediterranean Sea.

Oil spill drift predictions

The oil spill prediction system was crafted through the amalgamation of Cedre's proficiency in oil chemistry and Météo-France's prowess in meteorological and oceanic forecasting and modeling. This collaborative effort results in a robust operational service that is overseen by Météo-France. The modeling approach employed is based on the MOTHY model, which calculates the three-dimensional drift of both surface and sub-surface oil using a "superparticles" technique. At each time step, these superparticles are introduced based on predefined parameters such as location, release duration, and rate.

Container drift predictions

Shipping containers adrift at sea pose navigation hazards. Consequently, maritime authorities aim to provide navigators with container positions or facilitate their retrieval. This system employs a blend of modeling and analytical methodologies to predict the leeway rate (ratio of leeway speed to wind speed), contingent on the extent of immersion of the rectangular containers.

Search and Rescue targets

63 classes of SAR objects have been compiled by the U.S. Coast Guard as part of extensive field campaigns and have been generously made available. The database is continuously expanded through data obtained from sea experiments conducted by specialized agencies and through insights shared by Maritime Rescue Coordination Centers (MRCC). Presently, the database comprises 91 Search and Rescue (SAR) targets. Objects drift at an angle to the wind, and symmetry allows two drift directions, left and right of downwind. These two positions are not stable. The object can jibe, namely, change tack downwind. The frequency of these changes is an important element for modeling search areas. A Monte Carlo technique is used to generate an ensemble that accounts for the uncertainties in leeway drift properties and jibing frequency.