Publikationsdatum:
2017-04-01
Beschreibung:
Wind patterns in main and tributary valley systems undergo diurnal variations that are very dependent on the valley's dimensions. Characterising the down-valley winds is important for pollutant dispersion studies. It is also a challenge for numerical simulations. This paper uses KASCADE (KAtabatic winds and Stability over CAdarache for Dispersion of Effluents) observations to describe down-valley flow development and characteristics in two intersecting, shallow valleys of different sizes located in the pre-alpine region of South East France. The Durance Valley and its tributary valley, the Cadarache Valley, are different in depth (200 vs. 100 m depth, respectively), slope (0.2 vs. 1.2°), width (5 to 8 vs. 1 to 2 km) and length (〉50 vs. 6 km). Both down-valley flows were dominant features for the period of measurements. The distinct valley scales lead to different characteristics: the smaller Cadarache down-valley wind is primarily thermally driven and attains wind speeds of up to 1 - 4 m s –1 with its jet nose at around 30 m in height a.g.l. The flow at that height initiates 2 hours after sensible heat flux turnover, a timescale which relates to a linear wave solution for along-valley winds. The Durance down-valley wind involves larger scales - for both terrain features and large-scale circulation - and is related to a mountain-to-plain circulation. Its onset occurs therefore with a delay of ~6 hours after sunset. It reaches speeds of 4 - 8 m s –1 and a depth of 175 - 225 m a.g.l. Its highest occurrence is just after sunrise. In between the two valley winds, a shear layer is observed, the origin of which could be a combination of a Cadarache valley flow return current and a Durance down-valley wind stream re-directed by orography.
Print ISSN:
0035-9009
Digitale ISSN:
1477-870X
Thema:
Geographie
,
Physik
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