Ensemble Simulations of Convective Storms

This study presents ensemble simulations of idealized convective storms with the nonhydrostatic atmospheric COSMO model. Wind speed, temperature and humidity of the environmental sounding are perturbed for the ensemble generation. The impact of different perturbation amplitudes on the storm structure and evolution in the individual ensemble members and the resulting statistical ensemble characteristics are investigated. It was found that all three variables are suited for perturbation. Perturbations in the wind profile lead to differences in the vertical vorticity, which determine the storm structure, whereas temperature and humidity perturbations affect the convective available potential energy, the updrafts, and the vertical vorticity distribution. A combined perturbation of wind speed and temperature turned out to be particularly useful. The modeling setup, derived in this study, is judged as a suitable testbed for ensemble data assimilation methods, such as the Ensemble Kalman Filter.