Novel perspectives of jet stream climatologies and events of heavy precipitation on the alpine southside

In the last two decades, several studies have emphasized the relevance of the tropopause region for the dynamics of transient synoptic weather systems. In the two independent parts of this thesis, novel perspectives are explored of two salient topics of dynamical meteorology that are related to characteristic features at tropopause level. In the first part, the focus is on jet streams. Increased knowledge and understanding are sought related to their structure, geographical distribution, seasonal variation and dynamics. A novel type of event-based jet-stream climatology is presented for both hemispheres using ECMWF reanalysis data for the years 1979-1993. It involves the detection of transient jet streams based upon an objective criterion. The resulting space-time distribution of jets provides a rich data set for climatological studies. In the second part, a study is undertaken of the September 1993 and October 2000 heavy precipitation episodes on the Alpine southside that were associated with meridionally elongated intrusions of stratospheric air (upper-level precursors) over western Europe. The focus is on the relative role of the Mediterranean and the Atlantic as moisture suppliers for these extreme rain events. In a sequence of numerical simulation experiments, the effects of evaporation of both water basins upon the amount of precipitation in the Alpine region and the development o f the upper-level precursor are investigated.