Abstract : C.5
A 5-yr climatology of mesoscale environment associated with heavy precipitating events over southern France

Didier Ricard, Véronique Ducrocq, Ludovic Auger
GAME/CNRM (Météo-France, CNRS)

The southern France is regularly affected by heavy precipitating events (HPEs) potentially associated with devastating flash floods. The configuration of this area is propitious for triggering these HPEs. Indeed, the Mediterranean sea acts as a vast heat and moisture reservoir from which these systems pump their energy. Moreover, the steep orography (Massif Central, Pyrenees, South Alps) induces low-level convergence and favours ascending motion.

In this study, a climatological approach is developed to characterize the mesoscale environment in which these systems grow. This climatology based on 3D-var mesoscale data assimilation (VARPACK ALADIN) is realized for heavy precipitating events over a 5-year period considering cases with daily precipitation greater than 150 mm between 15 August and 31 December. The analysed data are surface mesonet, radiosounding and satellite data (QuikSCAT and SEVERI from 2005). The guess is provided by a 6-hour ALADIN forecast.

Then, different diagnostics are used to document the time evolution of mesoscale features associated with the HPEs such as low-level jets (intensity, orientation, moisture transport ... ) and other key ingredients (CAPE, Precipitable Water, moisture convergence ...). This is performed for the different phases of the life cycle which are determine from the observed hourly precipitation and lightning data.

To underline differences on these diagnostics according to the localisation of precipitation, four domains are considered (Languedoc-Roussillon, Cévennes-Vivarais, South Alps and Corsica areas). Thus, composite analyses are obtained by averaging these diagnostics for each domain and for each phase.