Local foehn effects in the Upper Isar Valley,Part 3: Additional investigations |
| |
Authors: | M Hornsteiner G Zängl |
| |
Institution: | (1) Meteorological Institute, University of Munich, Munich, Germany |
| |
Abstract: | Summary The present paper is the continuation of two recent studies investigating the foehn-like valley wind system around Mittenwald
(Bavarian Isar Valley). We deal with the synoptic/mesoscale conditions causing the local foehn (“Minifoehn”), considering
field campaigns from both the mesoscale and the climatological point of view. Furthermore, we describe the structure and further
features of the local foehn at smaller scales, using both the results of the VERTIKATOR field campaign and numerical simulations.
We obtain as a new result that the foehn-caused local warm air pool around Mittenwald induces slight nocturnal upvalley winds
between an adjacent valley basin located some 8 km north of Mittenwald and the basin of Mittenwald. Furthermore, a weak northerly
flow may also occur at Mittenwald prior to the onset of the Minifoehn. Numerical simulations indicate that the local pressure
gradient responsible for this phenomenon is related to a gravity wave forming over the hill range southwest of Mittenwald.
Observations within a five-year period indicate that Minifoehn frequently occurs when ambient winds coming from the southern
sector are predominant, but, contrary to deep foehn, weather conditions with northerly synoptic-scale flows do not necessarily
exclude the development of the local foehn which comes from the southwest. We also present further evidence that in the presence
of southerly synoptic-scale winds, orographic gravity waves interact with the drainage flow. Another new result is that strong
synoptic-scale westerly winds are able to suppress the occurrence of Minifoehn. In addition, the possible influence of the
Inn Valley wind system as well as dynamical differences between the thermally driven up- and downvalley winds are briefly
discussed. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|