Abstract : 1C.27
Statistical analysis of foehn in Altdorf, Switzerland

Hans Richner, Thomas Gutermann
Atmospheric and Climate Science, ETH Zurich

Since 1864, the occurrence of foehn in Altdorf is being monitored. Altdorf lies in the Reuss Valley. The line "Leventina" (the valley south of the Alps) -- "Reuss Valley" is the only valley combination in the Alpine region which is straight, almost perpendicular to the crest, and has only a single ridge.

The time series of foehn occurrence is analyzed with respect to diurnal and seasonal variations of foehn as well as with respect to the year-to-year changes. While the yearly and seasonal variations are clearly caused by the corresponding variations in synoptic patterns, diurnal changes can be explained by the interaction of local phenomena (such as mountain-valley wind systems) with the foehn flow.

An attempt is made to compare the statistical results with those found in the topographically more complicated Rhine Valley.

Of course, also here the obvious question is: "Did foehn occurrence change during the last 140 years, e.g., as result of the climatic change?" While a very small trend is noticeable, from the available data no significant shift can be found.