Original paper

Nature and climatology of Pfänderwind

Gohm, Alexander; Siller, Maria; Bär, Julius

Meteorologische Zeitschrift Vol. 24 No. 3 (2015), p. 243 - 259

30 references

published: Jul 16, 2015
published online: Feb 11, 2015
manuscript accepted: Nov 8, 2014
manuscript revision received: Nov 6, 2014
manuscript revision requested: Oct 28, 2014
manuscript received: Aug 24, 2014

DOI: 10.1127/metz/2015/0648

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Abstract

The characteristics and climatology of Pfänderwind, a largely unknown downslope windstorm near the town of Bregenz (Austria) at the entrance of the Rhine Valley, are investigated based on an eleven-year dataset of weather station observations and ERA-Interim reanalyses. The goal is to clarify the inconsistency in the definition of this phenomenon, to illuminate its dynamics, and to quantify its frequency of occurrence. It is shown that Pfänderwind has similarities to foehn but does occur for different synoptic-scale conditions. Moreover, two types of Pfänderwind have to be distinguished: Type 1, or classical Pfänderwind, is associated with easterly to northeasterly large-scale flow that crosses the Pfänder mountain range, descends in a foehn-like manner and causes moderate to strong winds in the town of Bregenz and its vicinity. The temperature anomaly induced at the surface by adiabatic warming is small as a result of weak low-level stability. Type-1 events occur on average 12 times per year, preferentially in spring, and most frequently between the afternoon and midnight. Type 2, or southeast Pfänderwind, is associated with westerly to southwesterly ambient winds near the main Alpine crest level. The Rhine valley is filled with cold air and in most cases south foehn is not present. However, the synoptic and meso-scale pressure gradient favours southerly ageostrophic flow in the Rhine Valley especially near the top of the cold-air pool. This flow passes the Gebhardsberg, the southwestern extension of the Pfänder mountain range, descends on its leeward side and causes strong foehn-like warming at the surface. However, southerly to southeasterly near-surface winds at Bregenz are rather weak. Type-2 events occur on average 40 times per year, most frequently between the evening and the early morning, and exhibit a weak seasonal dependence. More than half of all type-1 and type-2 events last only one or two hours.

Keywords

Bregenzer Fallwindfalscher FöhnOstföhndownslope windstormRhine valleyPfänder