On-line analysis of synoptic- and meso-scale flow features (Stefan Rüdisühli)
To study flow features such as cyclones, fronts, or orographic blockings from a climatological perspective, it is necessary to objectively identify and track them. As an example, one way to identify cyclones is by finding closed contours around minima in the surface pressure field. By applying an area overlap criterion to these fields at consecutive timesteps, the cyclones can then be tracked over time and space.
The goal of my current work is to to diagnose such features in continental-scale cloud-resolving regional climate simulations (-> link: "crCLIM" [https://www.ethz.ch/content/specialinterest/usys/c2sm/en/research/crCLIM.html]). The size of these simulations makes it is necessary to run the analysis tools on-line, i.e. in parallel to the model, because the amount of data required for off-line analysis is too large to write to disk. The plot shows minima (blue), maxima (black), and contours of pressure and illustrates the need to adapt existing tools originally written for coarser resolutions, in this case e.g. by applying a smoothing filter.
Ensemble prediction systems (Christina Klasa)
Quantitative precipitation forecasting is challenging due to the dependence of precipitation location and intensity on physical processes that occur on a large range of spatial and temporal scales. In ensemble forecasts initial conditions and, in case of a limited-area model, also lateral boundary conditions are perturbed. Many physical processes occur at scales that are not explicitly resolved by the model and that thus need to be parameterized. However, because parameterizations are just approximations, uncertainties also arise in this part of the model formulation. To address these model uncertainties, we use random perturbations of tendencies of the prognostic variables that are associated with the parameterizations. This project uses the COSMO-E ensemble, currently being developed at MeteoSwiss, to investigate different realizations of the random physics and the possible benefit in terms of forecast reliability, in particular for high-impact precipitation events in the Alpine region.
Heavy precipitation events in Switzerland (Nicolas Piaget)
Floods are among the most damaging natural hazards in the Alpine regions. They are caused by heavy precipitation events which are often strongly affected by the orographic effects. In order to estimate the hydrological risks of such events a good understanding of the factors governing precipitation is needed.
In this work, the sensitivity of extreme precipitation events to changes in specific humidity and temperature is examined, and in particular the role of the different scales (synoptic, meso and micro).
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