Jugend und Politik

Claußen, Bernhard

doi:10.1007/978-3-322-85702-6_17

Cited by 4 publications

(1 citation statement)

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“…The values of these constants have been the subject of some discussion (see, for example, Walmsley and Taylor 1996) but several studies have shown that Jackson and Hunt's (1975) original de nition (n D 1, c D 2k 2 , where k is the von Kármán constant) overestimates the inner-region depth (e.g. Jensen et al 1984;Claussen 1988). …”

Section: Introductionmentioning

confidence: 99%

Measurements of the near‐surface flow over a hill

Mobbs

Gardiner

2002

Quart J Royal Meteoro Soc

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SUMMARYThe near-surface ow over a hill with moderate slope and height comparable with the boundary-layer depth is investigated through eld measurements of the mean ow (at 2 m), surface pressure, and turbulent momentum ux divergence between 8 and 15 m. The measurements were made along an east-west transect across the hill Tighvein (height 458 m, approximate width 8 km) on the Isle of Arran, south-west Scotland, during two separate periods, each of around three-weeks duration. Radiosonde ascents are used to determine the variation of a Froude number, FL D U=NL, where U is the wind speed at the middle-layer height, h m , N is the mean Brunt-Väisälä frequency below this height and L is a hill length-scale. Measurements show that for moderately strati ed ows (for which FL & 0:25) a minimum in the hill-induced surface-pressure perturbation occurs across the summit and this is accompanied by a maximum in the near-surface wind speed. In the more strongly strati ed case (FL . 0:25) the pressure eld is more asymmetric and the lee-slope ow is generally stronger than on the windward slope. Such a ow pattern is qualitatively consistent with that predicted by strati ed linear boundary-layer and gravity-wave theories. The near-surface momentum budget is analysed by evaluating the dominant terms in a Bernoulli equation suitable for turbulent ow. Measurements during periods of westerly ow are used to evaluate the dominant terms, and the equation is shown to hold to a reasonable approximation on the upwind slope of the hill and also on the downwind slope, away from the summit. Immediately downwind of the summit, however, the Bernoulli equation does not hold. Possible reasons for this, such as non-separated sheltering and ow separation, are discussed.

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Section: Introductionmentioning

confidence: 99%