Post on 18-Jan-2016
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Storm surge forecast at Météo-FranceStorm surge forecast at Météo-France
Pierre DanielPierre Daniel
Storm surge model
• Two versions of one model:
Overseas territories (for tropical cyclones storm surges)
Metropolitan coasts
Model installation
Model equations
• Shallow water equations• Finite differences on a fix grid mesh (Arakawa C)• At bottom: Chezy condition• Wind stress: Smith and Sandwell formulation• Coast: normal componant of current is set to zero• Open boundary: inverted barometer effect + radiation
condition
• Inputs: wind, atmospheric pressure, bathymetry
Atmospheric forcing• Modified Holland model: pressure profile and gradient
wind• Information needed: position, intensity, size• Provided by cyclone advisories
• Example:• FORECAST VALID 21000Z 20.7S 165.8E.• MAX SUSTAINED WINDS OF 80 KT.• RADIUS OF 50 KT WINDS 65NE 40SE 25SW 40NW• RADIUS OF 34 KT WINDS 85NE 60SE 40SW 60NW
Bathymetry
• Hand extracted from nautical charts• 30 islands, grid mesh from 150 m to 2 km.• Examples:
Model calibration• On selected cyclones from 1975 to 1990• Very few tide gauges: 6 for 30 islands
Largest surge: 250 cm in Guadeloupe (Hugo, 1989)
Model forecasts
• Largest surges: Luis, 1995• estimated: 2 m in St Martin (2 m forecast)
•measured: 40 cm in Guadeloupe (35 cm forecast)
What is the best way to use the model ?
Real-time forecast accuracy• When a hurricane is crossing an island, a
small error in the trajectory forecast gives a large error in the space distribution of the surge.
Pre-computed storm surge data base• More than 1000 model runs for each island.• A data base available for graphical display on a computer.
Storm surge data base
Coastline of France• Same equations and numerical scheme• Wind stress: Wu formulation• Tide: 16 waves + 13 tide gauges• Calibration on selected situations (1987-1992)• In operation since October, 1999.
• Under development: Improvement of the wind interpolation (spatial and temporal).
• Sensitivity to atmospheric forcing: ECMWF, ARPEGE, ALADIN.
Surges with ECMWF analyses (6 hours)
Surges at La Rochelle (ECMWF analyses – 6 hours)
Temporal frequency impact of atmospheric forcing at Le Verdon (ALADIN - December 27th, 1999)
Next steps
• Mediterranean sea
• North sea
• Wave surges in the lagoons
• Real time access to tide gauge data
• Data assimilation