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Article Dans Une Revue La Houille Blanche - Revue internationale de l'eau Année : 2004

The 8-9 September 2002 extreme flash-flood : Meteorological description and mesoscale simulations

Résumé

The Southeastern France is prone to heavy precipitating events. A major event has occurred the 8-9th September 2002, with maxima of accumulated rainfall totals having reached locally 600-700 mm; there were more than 20 deaths. The high resolution non-hydrostatic model MESO-NH (2.4 km grid-mesh) has been run a posteriori on this case. It has been found that the high resolution simulation may significantly improves the quantitative precipitation forecast of the event. A sensitivity study to initial conditions has been conducted and shows clearly that mesoscale data assimilation is the most efficient to improve the short range forecast : assimilation of mesonet surface observations, radar and satellite data helps to improve significantly the location of the precipitation maximum. The high resolution model has been also used to study the event, and in particular to understand the relative unusual location of the largest precipitation over the upwind lower mountainous area of the Gard department rather than over the Massif Central crests. The location of the most active convection is explained by a cold pool beneath the simulated storm that faced the low-level moist and unstable southeastern flow from Mediterranean sea. This density current, produced by the evaporation, sublimation and melting of precipitation, forced the unstable air to lift, generating therefore continuously new convective cells at the leading edge of the cold pool.
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Dates et versions

halsde-00441440 , version 1 (16-12-2009)

Identifiants

  • HAL Id : halsde-00441440 , version 1

Citer

Véronique Ducrocq, C. Lebeaupin, Thierry Thouvenin, Hervé Giordani, Katia Chancibault, et al.. The 8-9 September 2002 extreme flash-flood : Meteorological description and mesoscale simulations. La Houille Blanche - Revue internationale de l'eau, 2004, 6, pp.86-92. ⟨halsde-00441440⟩
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