Lightning and Cloud Electrification in the COSMO Numerical Weather Prediction Model

Severe weather and deep convection are often related to thunderclouds which can besides the hydrometeorological extremes can produce lightening. Lightening is responsible not only for wildfires but also for many casualties which makes it one of the most dangerous meteorological natural hazards worldwide. To be able to reduce the high number of human losses related to lightening, a precise prediction of the phenomenon is needed. However, in the Czech Republic (Central Europe), the lightening has previously been predicted only implicitly from the outputs of the models based on the forecasted deep convection. In this contribution, we present a recently developed explicit treatment of lightening and associated cloud electrification that has been implemented in the COSMO non-hydrostatic numerical weather prediction model. The implemented model is a three-dimensional model which includes parameterizations, several of these are obtained from laboratory experiments. The treatment of the cloud electrification consists of the widely accepted non-inductive graupel-ice collision mechanism, which enables for an explicit charge separation and description of the processes of small atmospheric ions in the clouds. Lightening is also explicitly treated in the implemented model, based on the common bidirectional concept of the leader of flashes which enables to model the vertical propagation of the discharge channels initiated along the electric field. The propagation of the flashes in other than vertical direction is given by a probabilistic branching scheme which is based on dielectric breakdown concept and provides a more realistic simulation of the flash form. Both the cloud electrification and the lightening submodels implemented into the COSMO model have been tested on the observed data during the three intense convective events in 2016 that led to heavy rainfall, flash floods, and regionally severe material damages and other economic losses in the Czech Republic. The explicit treatment of cloud electrification and lightening improves the description of the processes in the COSMO model which enhances its accuracy. The future research will further investigate the practical use of the implemented model.