Abstract : 2E.9
Pluviometric regime associated to shallow convection in mountainous area

Angélique Godart, Sandrine Anquetin, Etienne Leblois

It is well known that relief plays a particular part in rain triggering. Our study is focussed on the Cévennes-Vivarais area where the topography and the specific meteorological situation lead to an important hydrometeorological potential risk in this region, which need to be better understand. From a climatologic point of view, we consider that these rains result in two kinds of convection: a deep convection governed by synoptic conditions in which relief has little impact and a shallow convection strongly controlled by the circulation of air within relief. This study aims at understanding and analysing the atmospheric parameters that control shallow convection in this region. The methodology is first based on the exploration of the meteorological and pluviometric data bases in order to identify the meteorological characteristics (temperatures, relative humidity, wind velocity and direction, CAPE, CIN, wind shear, stability,…) associated with shallow convection. Then we analyse soundings profiles at Nîmes, based on meteorological and pluviometric criterions settled in the first step. From this second step, 79 shallow convective soundings are then analysed. Our results show that shallow convective events can be characterized by a vertical profile of relative humidity, wind velocity, wet bulb potential temperature, and by the value and nature of vertical wind shear and the height of stable layer. Mean values and percentiles of other atmospheric parameters have been found. From this study, we propose a generic sounding characterised of shallow convection in this region. The next step is dedicated to the understanding of the meteorological mechanisms associated to shallow convection. This is done using the MesoNH meteorological model forced with the generic sounding. Thanks to these simulations we can study the sensibility of orographic rain and its organization in bands to relative humidity, wind velocity and the other parameters.