Analysis of simulation of lightning in a cold-based convective storm

Sammanfattning: In this paper a simulation of a convective cell of a thunderstorm system observed 19th of June 2000 during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) field campaign is being analysed. The storm system has been simulated with an Aerosol-Cloud model and the analysis is based on the output data. The analysis spans over 30 minutes which covers the mature stage and the beginning of the dissipation stage of the storm cell. A pronounced updraft is found in the centre of the cell with vertical wind speed reaching 17 m/s. The updraft ascends through a ‘mixed-phased’ region which is found at an altitude between 3 km to 9 km above mean sea level. The electrification of the storm cell is caused by microphysical species of ice attaining an electric charge due to rebounding collisions and rubbing against one another which gives rise to a charge separation. The analysis reveals that mainly ice particles and snow was found to be negatively charged while graupel positively. It was found that regions where the magnitude of the electric field is strongest is between regions of positive and negative charge which also coincides with the location where trigger points for light flashes were found. A total of 265 light flashes were found throughout a time period of 20 minutes which gives a rate of 13.25 light flashes per minute. A correlation between amount of lightning flashes and average magnitude of the electric field was found. It was found that the amount of lightning flashes increases as a result of the increased average magnitude of the electric field.