2015, Wapler, Kathrin, Harnisch, Florian, Pardowitz, Tobias, Senf, Fabian

Two severe summer-time convective events in Germany are investigated which can be classified by the prevailing synoptic conditions into a strong and a weak forcing case. The strong forcing case exhibits a larger scale precipitation pattern caused by frontal ascent whereas scattered convection is dominating the convective activity in the weak forcing case. Other distinguished differences between the cases are faster movement of convective cells and larger regions with significant loss mainly due to severe gusts in the strong forcing case. A comprehensive set of various observations is used to characterise the two different events. The observations include measurements from a lightning detection network, precipitation radar, geostationary satellite and weather stations, as well as information from an automated cell detection algorithm based on radar reflectivity which is combined with severe weather reports, and damage data from insurances. Forecast performance at various time scales is analysed ranging from nowcasting and warning to short-range forecasting. Various methods and models are examined, including human warnings, observation-based nowcasting algorithms and high-resolution ensemble prediction systems. The analysis shows the advantages of a multi-sensor and multi-source approach in characterising convective events and their impacts. Using data from various sources allows to combine the different strengths of observational data sets, especially in terms of spatial coverage or data accuracy, e.g. damage data from insurances provide good spatial coverage with little meteorological information while measurements at weather stations provide accurate but pointwise observations. Furthermore, using data from multiple sources allow for a better understanding of the convective life cycle. Several parameters from different instruments are shown to have a predictive skill for convective development, these include satellite-based cloud-top cooling rates as measure for intensive convective growth, 3D-radar reflectivity, mesocyclone detection from doppler radar, overshooting top detection or lightning jumps to evaluate storm intensification and formation of severe weather. This synergetic approach can help to improve nowcasting algorihtms and thus the warning process. The predictability of the analysed severe convective events differs with different types of forcing which is reflected in both, convective-scale ensemble prediction system forecasts and human weather warnings. Human warnings show larger false alarm rates in the weak forcing case. Ensemble predictions are able to capture the characteristics of the convective precipitation. The forecast skill is connected strongly to the synoptic situation and the presence of large-scale forcing increases the forecast skill. This has to be considered for potential future warn-on-forecast strategies.

2014, Weissmann, Martin, Göber, Martin, Hohenegger, Cathy, Janjic, Tijana, Keller, Jan, Ohlwein, Christian, Seifert, Axel, Trömel, Silke, Ulbrich, Thorsten, Wapler, Kathrin, Bollmeyer, Christoph, Deneke, Hartwig

The Hans-Ertel Centre for Weather Research is a network of German universities, research institutes and the German Weather Service (Deutscher Wetterdienst, DWD). It has been established to trigger and intensify basic research and education on weather forecasting and climate monitoring. The performed research ranges from nowcasting and short-term weather forecasting to convective-scale data assimilation, the development of parameterizations for numerical weather prediction models, climate monitoring and the communication and use of forecast information. Scientific findings from the network contribute to better understanding of the life-cycle of shallow and deep convection, representation of uncertainty in ensemble systems, effects of unresolved variability, regional climate variability, perception of forecasts and vulnerability of society. Concrete developments within the research network include dual observation-microphysics composites, satellite forward operators, tools to estimate observation impact, cloud and precipitation system tracking algorithms, large-eddy-simulations, a regional reanalysis and a probabilistic forecast test product. Within three years, the network has triggered a number of activities that include the training and education of young scientists besides the centre's core objective of complementing DWD's internal research with relevant basic research at universities and research institutes. The long term goal is to develop a self-sustaining research network that continues the close collaboration with DWD and the national and international research community.

2017, Heinze, Rieke, Dipankar, Anurag, Henken, Cintia Carbajal, Moseley, Christopher, Sourdeval, Odran, Trömel, Silke, Xie, Xinxin, Adamidis, Panos, Ament, Felix, Baars, Holger, Barthlott, Christian, Behrendt, Andreas, Blahak, Ulrich, Bley, Sebastian, Brdar, Slavko, Brueck, Matthias, Crewell, Susanne, Deneke, Hartwig, Di Girolamo, Paolo, Evaristo, Raquel, Fischer, Jürgen, Frank, Christopher, Friederichs, Petra, Göcke, Tobias, Gorges, Ksenia, Hande, Luke, Hanke, Moritz, Hansen, Akio, Hege, Hans-Christian, Hoose, Corinna, Jahns, Thomas, Kalthoff, Norbert, Klocke, Daniel, Kneifel, Stefan, Knippertz, Peter, Kuhn, Alexander, van Laar, Thriza, Macke, Andreas, Maurer, Vera, Mayer, Bernhard, Meyer, Catrin I., Muppa, Shravan K., Neggers, Roeland A.J., Orlandi, Emiliano, Pantillon, Florian, Pospichal, Bernhard, Röber, Niklas, Scheck, Leonhard, Seifert, Axel, Seifert, Patric, Senf, Fabian, Siligam, Pavan, Simmer, Clemens, Steinke, Sandra, Stevens, Bjorn, Wapler, Kathrin, Weniger, Michael, Wulfmeyer, Volker, Zängl, Günther, Zhangl, Dan, Quaase, Johannes

Large-eddy simulations (LES) with the new ICOsahedral Non-hydrostatic atmosphere model (ICON) covering Germany are evaluated for four days in spring 2013 using observational data from various sources. Reference simulations with the established Consortium for Small-scale Modelling (COSMO) numerical weather prediction model and further standard LES codes are performed and used as a reference. This comprehensive evaluation approach covers multiple parameters and scales, focusing on boundary-layer variables, clouds and precipitation. The evaluation points to the need to work on parametrizations influencing the surface energy balance, and possibly on ice cloud microphysics. The central purpose for the development and application of ICON in the LES configuration is the use of simulation results to improve the understanding of moist processes, as well as their parametrization in climate models. The evaluation thus aims at building confidence in the model's ability to simulate small- to mesoscale variability in turbulence, clouds and precipitation. The results are encouraging: the high-resolution model matches the observed variability much better at small- to mesoscales than the coarser resolved reference model. In its highest grid resolution, the simulated turbulence profiles are realistic and column water vapour matches the observed temporal variability at short time-scales. Despite being somewhat too large and too frequent, small cumulus clouds are well represented in comparison with satellite data, as is the shape of the cloud size spectrum. Variability of cloud water matches the satellite observations much better in ICON than in the reference model. In this sense, it is concluded that the model is fit for the purpose of using its output for parametrization development, despite the potential to improve further some important aspects of processes that are also parametrized in the high-resolution model.