XV International Conference on Atmospheric Electricity, 15-20 June 2014, Norman, Oklahoma, U.S.A. Simulations with MesoNH of the electrical features of two precipitating events observed during HyMeX (2012) in South-Eastern France Jean-Pierre Pinty 1 * , Eric Defer 2 , Paul Krehbiel 3 , William Rison 3 , Wolfgang Schultz 4 , Michel Chong 1 , Ronald Thomas 3 and Evelyne Richard 1 1 Laboratoire d’A´ erologie, 14 avenue E. Belin, 31400 Toulouse, France 2 LERMA, 77, Avenue Denfert-Rochereau, 75014 Paris, France 3 New Mexico Tech., Socorro, NM, USA 4 ¨ OVE-ALDIS, Vienna, Austria ABSTRACT: CELLS, the explicit electrical scheme of MesoNH is used to simulate the temporal evolu- tion of the electrical charges, to compute the ambient electric field and to trigger lightning flashes, ultimately. The scheme is highly coupled to the current ICE3 microphysical scheme to generate locally the electrical charges by non-inductive processes and to disseminate these charges by various microphysical processes in order to build positive-negative regions of charges at cloud scale. Simulations were performed with the grid-nesting facility at 4 km and 1 km resolution to reach the km scale at which simulated flashes could be resolved. The electrical scheme was run for several hours on a large domain of nearly 400x400x50 grid points using the Meteo-France Arome analyses that encompass the HyMeX (HYdrological cycle in the Mediterranean EXperiment) SOP1 (Special Observation Period 1 in 2012) field experiment area. Results are analyzed and compared to records of two lightning detection net- works: EUCLID (2D accurate counts) and HyLMA (3D mapping of the flashes). LMA data are especially useful to observe intra-cloud flashes and to document the polarity of the cloud layers where flashes prop- agate, thus giving a precious indication for comparing the polarity of the simulated cloud regions, as well as the triggering altitude and horizontal extent of all the flashes. First promising results of two contrasting precipitating cases, isolated convection and 8 hour precipitating event of HyMeX-SOP1, are discussed. INTRODUCTION During the first Special Observing Period (SOP1) of the HYdrological cycle in Mediterranean EX- periment (HyMeX, see Ducrocq [2013]) a network of 12 LMA stations were deployed and operated in the South East flank of the Massif Central, a mountaneous region in France. The purpose was to investigate the electrical properties of heavily precipitating orographic clouds that result from the lifting of moist warm air flowing from the next Mediterranean sea. A unique dataset of lightning flashes generated by orograhic clouds was produced for the first time in Europe and for the purpose here to evaluate an explicit electrical scheme in a mesoscale model running under real meteorological conditions. The electrical scheme (CELLS, see Barthe et al. [2012]) of the cloud-resolving model MesoNH was developed 1/ to simulate the temporal evolution of the charges carried by the hydrometeors and by the ions, 2/ to compute the ambient electric field and ultimately, 3/ to trigger the lightning flashes, to close the electrical charge budget. The scheme is tightly coupled to the current 1-moment microphysical scheme (ICE3) of MesoNH to separate locally the electrical charges by non-inductive and inductive processes and also to disseminate these charges among the drop/ice particles by the various microphysical mechanisms of ICE3 in order to build positive-negative regions of charges at cloud scale. * Corresponding author, email: pinjp@aero.obs-mip.fr, Postal address: Laboratoire d’A´ erologie, 14, avenue E. Belin, 31400 Toulouse, France 1