Transcript Storm surge forecast at Météo-France Pierre Daniel

Storm surge forecast at Météo-France
Pierre Daniel
Storm surge model
• Two versions of one model:
 Overseas territories (for tropical cyclones
storm surges)
 Metropolitan coasts
Model installation
Model equations
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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:
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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
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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