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.
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