LIGHTNING PARAMETRIZATION IN NUMERICAL MODELS: DESCRIPTION AND RESULTS FROM BRAMS AND AN 1D CLOUD MODEL

Abstract- Numerical schemes of cloud electrification and lightning have been implemented into two numerical models at the University of Sao Paulo: the mesoscale Brazilian Regional Atmospheric Modelling System (BRAMS), and the one-dimensional cloud model of Ferrier and Houze (1989). Both cloud models have electrical charge separation based on non-inductive collisions between ice particles found in various laboratory studies. The resulting electric field is calculated at each time step and a lightning is triggered when this local field overcomes the break-even electric field. In the 1D cloud model, the lightning propagates bidirectionally (upward and downward), neutralizing charges along the channel until the electric field reduces to 15 kVm-1. In the BRAMS model, the lightning is propagated bidirectionally towards two main exceeding net charge regions until the magnitude of the electric field reduces to 20 kVm-1. At this point the lightning channel is branched into streamers where the total net charge density is greater then 0.5 nCm-3, and the charges are neutralized along the whole lightning path. These models were used to simulate thunderstorm conditions observed during the wet and dry-to-wet seasons of southwestern Amazon. Both models were able to simulate the literature known tripolar and dipolar structures of thunderstorms, and other more complicated multipolar structures.