Abstract
Abstract. Over the Cévennes–Vivarais region in southern France 5 h intensive rainfall covering an area of 1000 km2 with more than 50 mm of rain accumulation was observed during IOP7a of HyMeX. This study evaluates the performance of a bin-resolved cloud model for simulating this heavy-precipitation event. The simulation results were compared with observations of rain accumulation, radar reflectivity, temporal and spatial evolution of precipitation, 5 min rain rates, and raindrop size distributions (RSDs). The different scenarios for aerosol number concentrations range from 1000 to 2900 cm−3 and represent realistic conditions for this region. Model results reproduce the heavy-precipitation event with respect to maximum rain intensity, surface area covered by intense rain and the duration, as well as the RSD. Differences occur in the short-term rainfall rates, as well as in the drop number concentration. The cloud condensation number concentration has a notable influence on the simulated rainfall, on both the surface amount and intensity but also on the RSD properties, and should be taken into account in microphysics parameterizations.
Highlights
Heavy precipitation often occurs in autumn in the Cévennes– Vivarais (CV) region in southern France, frequently resulting in casualties in part due to difficulties of operational weather forecast models to predict location, timing and amplitude for timely alerts (e.g. Sénési et al, 1996; Romero et al, 2000; Delrieu et al, 2005; Silvestro et al, 2012; Rebora et al, 2013)
We focus on the following questions: is a detailed cloud description for all hydrometeor spectra suited to quantitatively reproduce rain accumulations, rain size distribution, and spatial and temporal variability that were observed by rain gauges, disdrometers and ground radars?
A major objective of this study was to test if a bin-resolved microphysics module in a 3D mesoscale model is successful in reproducing a real case of intense precipitation usually observed over the western Mediterranean basin
Summary
Heavy precipitation often occurs in autumn in the Cévennes– Vivarais (CV) region in southern France, frequently resulting in casualties in part due to difficulties of operational weather forecast models to predict location, timing and amplitude for timely alerts (e.g. Sénési et al, 1996; Romero et al, 2000; Delrieu et al, 2005; Silvestro et al, 2012; Rebora et al, 2013). The model studies performed in the HyMeX context applied the one-moment ICE3 scheme (Pinty and Jabouille, 1998), and the work of Taufour et al (2018) compares the two-moment scheme LIMA (Vié et al, 2016) The form of these prescribed spectra can deviate considerably from observed ones, several simulated bulk parameters, like radar reflectivity, rain and ice water content, can sometimes give values similar to the observations. Aerosol–cloud modelling, needs initial information about cloud condensation nuclei prevailing in the atmosphere prior to the cloud development These data were available during HyMeX as measurements of the aerosol particle spectra were performed by ground-based and airborne observations during the entire experimental period.
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