A wintertime case study on the impact of ice particle habits on simulated clouds and precipitation

Ice particles are considered in prevalent cloud microphysical parametrisation schemes in a simplified way by assigning them certain fixed forms, whereas in the atmosphere they occur in various different shapes. In this study, the sensitivity of cloud and precipitation properties to the selected interpretation of the ice particle shape is investigated with the help of simulations of a wintertime weather episode using the mesoscale weather forecast model ‘Lokal–Modell’ of the DWD. The results show that the interpretation of the particular ice particle type has a clear impact on the local surface precipitation rates while the area mean surface precipitation is only slightly affected. Most striking, however, is the influence on the simulated masses of cloud water in the atmosphere. To avoid the prescription of a fixed ice particle shape, a parametrisation variant is presented to account for the variation of ice particles' shape according to their growth history.