Rainfall regimes associated with banded convection in the Cévennes-Vivarais area

Abstract : It is well known that relief plays an important part in the triggering and enhancement of rainfall. Our study is focussed on the southeastern part of France where the topography and the specific meteorological conditions lead to an important hydrometeorological potential risk. From a climatologic point of view, we consider that these rainfall events arise from two kinds of convection: a deep convection essentially governed by synoptic conditions and where the relief has little direct impact and a shallow convection which is strongly controlled by the air circulation within the relief that leads to banded rain patterns. This study aims at understanding and analysing the atmospheric variables that control banded convection in this region. The methodology is first based on the exploration of the meteorological and rainfall data bases in order to identify the meteorological characteristics associated with this convection. Our results show that banded convection events can be characterized by specific vertical profiles of the dynamics variables (wind velocity, shear) and thermodynamic variables (humidity and wet bulb potential temperature profiles, stratification). We thus propose a generic sounding that is used as an input to the MesoNH meteorological model. Preliminary simulation results show a banded organisation of rainfall, which confirms our selection and allow for sensibility studies and further investigations of meteorological characteristics associated with this particular precipitation pattern.