Valley-wind characteristics in the Alpine Rhine Valley: Measurements with a wind-temperature profiler in comparison with numerical simulations

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Abstract:

This study investigates the valley-wind system of the Alpine Rhine Valley on the basis of measurements with a wind-temperature radar combined with high-resolution numerical simulations. It is found that the valley-wind circulation follows a very regular pattern on synoptically undisturbed days. In particular, the times at which the wind direction switches from up- to downvalley and vice versa and the wind speeds in the lower part of the valley-wind layer exhibit only a minor day-to-day variability. The model results indicate that in the exit region of the Rhine Valley, the nocturnal downvalley flow is much stronger than the daytime upvalley flow. Towards the interior of the valley, this asymmetry diminishes. These differences are related to variations of the valley width and to the impact of the tributaries. Along-valley variations of the near-surface wind speed are found to be associated with variations of the nocturnal surface temperatures. Significant near-surface winds reduce the nocturnal cooling due to increased vertical mixing.

German
In der vorliegenden Arbeit wird das Talwindsystem des alpinen Rheintals mit Hilfe von Messungen mit einem Wind-Temperatur-Radar sowie hochaufgelösten numerischen Simulationen untersucht. Es zeigt sich, dass die Talwindzirkulation an synoptisch ungestörten Tagen sehr regelmäßig abläuft. Insbesondere unterliegen die Zeiten des Umschlagens von Taleinzu Talauswind und umgekehrt sowie die Windgeschwindigkeiten im unteren Teil der Talwindschicht nur geringen Schwankungen von Tag zu Tag. Die Modellergebnisse zeigen, dass in der Mündungsregion des Rheintals der Talauswind wesentlich stärker ist als der Taleinwind. Diese Asymmetrie, die sich zum Talinneren hin verringert, ist auf Variationen der Talbreite und auf den Einfluss der Seitentäler zurückzuführen. Außerdem zeigt sich, dass Unterschiede der bodennahen Windgeschwindigkeit entlang des Tales mit Unterschieden der bodennahen nächtlichen Temperatur verbunden sind, da stärkerer Wind infolge stärkerer vertikaler Durchmischung die nächtliche Abkühlung verringert.

Document Type: Research Article

DOI: http://dx.doi.org/10.1127/0941-2948/2006/0110

Publication date: April 1, 2006

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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