Lightning modelling in numerical weather prediction

Abstract

The explicit representation of the atmospheric electric field in numerical weather prediction models is a current challenge. This representation will allow a physically based lightning forecast. Present study aims to assess the performance of the Cloud ELectrification and Lightning Scheme (CELLS) [1] coupled to the Meso-NH atmospheric mesoscale research model [2] in simulating Cloud-to-Ground (CG) flashes. The 17th June 2017 fire events over central Portugal (including the dramatic Pedrogão Grande wildfire) were considered as a real case study. According to an official report of the Portuguese authorities, nine ignition points were reported during that afternoon, some of them caused by lightning. The study discusses the atmospheric conditions that were favorable to lightning flashes production, as well as the possibility to correctly diagnose cloud-to-ground (CG) flashes using high resolution simulations. The simulation was configured with two nested domains of 4 km and 1 km horizontal resolution (Figure 1) and 50 vertical levels, with the innermost domain centred in the area where forest fires occurred. The description of the electrical state of a thunderstorm is based on the monitoring of the electrical charge densities, the computation of the electric field and the production of lightning flashes. The cloud charging involves mostly the non-inductive mechanism, and both Intra-Cloud (IC) and Cloud-toGround (CG) flashes are considered. As shown in [3], the model reproduced an extreme dry thunderstorm environment, responsible for a perfect scenario to natural ignition and fire propagation. The spatial distribution of Meso-NH-CELLS simulated CG lightning showed a good agreement with the lightning flashes obtained from the national lightning detection system.