Articles | Volume 15, issue 21
Atmos. Chem. Phys., 15, 12231–12249, 2015

Special issue: Hydrological cycle in the Mediterranean (ACP/AMT/GMD/HESS/NHESS/OS...

Atmos. Chem. Phys., 15, 12231–12249, 2015

Research article 04 Nov 2015

Research article | 04 Nov 2015

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

C. Flamant1, J.-P. Chaboureau2, P. Chazette3, P. Di Girolamo4, T. Bourrianne5, J. Totems3, and M. Cacciani6 C. Flamant et al.
  • 1Sorbonne Universités, UPMC Université Paris 06, CNRS and UVSQ, UMR 8190 LATMOS, Paris, France
  • 2Laboratoire d'Aérologie, Université of Toulouse and CNRS, Toulouse, France
  • 3LSCE, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 4SI-Università degli Studi della Basilicata, Potenza, Italy
  • 5CNRM, Météo-France-CNRS, Toulouse, France
  • 6Dipartimento di Fisica – Università di Roma "Sapienza", Rome, Italy

Abstract. The study is focused on Intensive Observation Period (IOP) 14 of the Hydrological Cycle in the Mediterranean Experiment first Special Observing Period (HyMeX SOP 1) that took place from 17 to 19 October 2012 and was dedicated to the study of orographic rain in the Cévennes–Vivarais (CV) target area. During this IOP a dense dust plume originating from northern Africa (the Maghreb and Sahara) was observed to be transported over the Balearic Islands towards the south of France. The plume was characterized by an aerosol optical depth between 0.2 and 0.8 at 550 nm, highly variable in time and space over the western Mediterranean Basin. The impact of this dust plume, the biggest event observed during the 2-month-long HyMeX SOP 1, on the precipitation over the CV area has been analyzed using high-resolution simulations from the convection permitting mesoscale model Meso-NH (mesoscale non-hydrostatic model) validated against measurements obtained from numerous instruments deployed specifically during SOP 1 (ground-based/airborne water vapor and aerosol lidars, airborne microphysics probes) as well as space-borne aerosol products. The 4-day simulation reproduced realistically the temporal and spatial variability (including the vertical distribution) of the dust. The dust radiative impact led to an average 0.6 K heating at the altitude of the dust layer in the CV area (and up to +3 K locally) and an average 100 J kg−1 increase of most unstable convective available potential energy (and up to +900 J kg−1 locally) with respect to a simulation without prescribed dust aerosols. The rainfall amounts and location were only marginally affected by the dust radiative effect, even after 4 days of simulation. The transient nature of this radiative effect in dynamical environments such as those found in the vicinity of heavy precipitation events in the Mediterranean is not sufficient to impact 24 h of accumulated rainfall in the dust simulation.

Short summary
We analyze the direct radiative impact of an intense African dust plume on orographic precipitation in the western Mediterranean in the fall of 2012 using high-resolution simulations from a convection permitting mesoscale model validated against measurements acquired during the first special observation period of HyMeX. We show that the dust's direct radiative effect in such a dynamical environment is not sufficient to impact 24h of accumulated rainfall over the Cevennes in the dust simulation.
Final-revised paper