Alpine weather and climate

The weather and climate in central Europe is strongly influenced by the Alps. For instance, the mean precipitation in Central Europe clearly reflects the outline of the Alpine barrier, or heavy precipitation is triggered by the mountainous barrier. Furthermore, many wind systems, e.g., foehn, are directly linked to the complex topography of the Alps, with many inner-Alpine valleys and mountain ridges. Of course, this complexity also has its impact on the predictability of Alpine weather, and hence poses a particular challenge for NWP models.

The research in our group during the recent few years has addressed several aspects of Alpine meteorology. First, 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 orographic effects. The dynamics of such events is studied in great detail in our group. In particular we consider the role and link of the different temporal and spatial scales (synoptic, meso and micro) and how they lead to flooding events. Second, we investigate how the airstreams impinging on the Alpine barrier are affected, e.g., whether they are horizontally deflected (orographic blocking) or surmount the Alpine crest. This flow regime strongly influences, e.g., the spatial pattern of precipitation and is also decisive in the formation of lee-cyclones in the gulf of Genoa or Mistral jets between the western Alps and the Massif Central. Third, foehn winds affect both the northern and southern parts of Switzerland. We study both the climatological aspects of foehn flow in the Alpine valleys, and also the physical processes related to foehn dynamics, thermodynamics and predictability. Finally, in a fourth research topic, hail formation in the Alpine region is considered. Hail cells are tracked in space and time, and their evolution (pathway, intensifying and weakening phases) is studied in detail to determine how it is determined by the complex topographic environment. In addition to the process understanding on hail formation, the predictability of hail cells in complex topography is investigated based on ensemble NWP simulations, and the expected changes of hail tracks, intensities and spatial frequencies in a warming climate are assessed.

The group is addressing the overall goals listed above in several complementary ways: climatological studies based on NWP (ensemble) forecast and reanalysis data sets are used to compile extensive climatologies, e.g., of foehn flows under varying synoptic conditions. More process-oriented research is based on high-resolution numerical modeling, in particular with the COSMO NWP model, and it relies also extensively on our Lagrangian analysis tool LAGRANTO. Multi-year COSMO simulations under present-day and future climate conditions are used to assess how weather and climate in the Alpine change in a warming climate.
The senior scientist working in this research area and their core themes are Michael Sprenger (orographic blocking and foehn dynamics), Iris Thurnherr (high-resolution weather and climate COSMO simulations), Ellina Agayar (hail and heavy precipitation), and Ruoyi Cui (hail and heavy precipitation).

The PhD projects conducted in this research area are outlined below: