The radiative impact of desert dust on orographic rain in the Cévennes-Vivarais area: A case study from HyMeX

摘要

The study is focused on Intensive Observation\udPeriod (IOP) 14 of the Hydrological Cycle in the Mediterranean\udExperiment first Special Observing Period (HyMeX\udSOP 1) that took place from 17 to 19 October 2012 and was\uddedicated to the study of orographic rain in the Cévennes–\udVivarais (CV) target area. During this IOP a dense dust\udplume originating from northern Africa (the Maghreb and\udSahara) was observed to be transported over the Balearic\udIslands towards the south of France. The plume was characterized\udby an aerosol optical depth between 0.2 and 0.8\udat 550 nm, highly variable in time and space over the western\udMediterranean Basin. The impact of this dust plume,\udthe biggest event observed during the 2-month-long HyMeX\udSOP 1, on the precipitation over the CV area has been\udanalyzed using high-resolution simulations from the convection\udpermitting mesoscale model Meso-NH (mesoscale\udnon-hydrostatic model) validated against measurements obtained\udfrom numerous instruments deployed specifically during\udSOP 1 (ground-based/airborne water vapor and aerosol\udlidars, airborne microphysics probes) as well as space-borne\udaerosol products. The 4-day simulation reproduced realistically\udthe temporal and spatial variability (including the vertical\uddistribution) of the dust. The dust radiative impact led to\udan average 0.6K heating at the altitude of the dust layer in the\udCV area (and up to C3K locally) and an average 100 Jkg1\udincrease of most unstable convective available potential energy\ud(and up to C900J kg1 locally) with respect to a simulation\udwithout prescribed dust aerosols. The rainfall amounts\udand location were only marginally affected by the dust radiative\udeffect, even after 4 days of simulation. The transient nature\udof this radiative effect in dynamical environments such\udas those found in the vicinity of heavy precipitation events in\udthe Mediterranean is not sufficient to impact 24 h of accumulated\udrainfall in the dust simulation.