Abstract
Detailed measurements of profiles of mean and turbulent variablesthrough the nocturnal stable boundary layer over a valley arepresented. Two nights of data are analysed in detail, one with only aweakly stable boundary layer and one with a strongly stable boundarylayer. The weakly stratified night shows high levels of turbulence inwhich the flow remains attached to the valley and the boundary layeracts as a single coherent layer. On the strongly stratified night, twoflow regimes are identified: attached flow, as on the weaklystratified night, and decoupled flow in which the air in the valleybecomes so dynamically stable that there is no turbulent interactionwith the mean flow aloft. Because the valley is sloping, the decoupledlower stagnant air then forms a drainage current. We find that theFroude number evaluated at the hill height, FH = U(H)/N(H) H,diagnoses the flow regime: when FH = 2, the flow remainsattached and when FH ≲ 2 the flow in the valley becomesdecoupled from the flow aloft. The dynamics of the flow regimes areshown to be understandable in terms of the gradient Richardson number,which indicates the turbulent mixing. We show that the gradientRichardson number is a key parameter in diagnosing each flow regime.
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References
Baines, P. G.: 1995, Topographic Effects in Stratified Flows, Cambridge University Press, 482 pp.
Belcher, S. E. and Hunt, J. C. R.: 1998, ‘Turbulent Flow over Hills and Waves’, Annu. Rev. Fluid Mech. 30, 507–538.
Belcher, S. E. and Wood, N.: 1996, ‘Form and Wave Drag due to Stably Stratified Turbulent Flow over Low Ridges’, Quart. J. Roy. Meteorol. Soc. 122, 863–902.
Derbyshire, S. H.: 1990, ‘Nieuwstadt's Stable Boundary Layer Reviseted’, Quart. J. Roy. Meteorol. Soc. 116, 127–158.
Derbyshire, S. H.: 1995, ‘Stable Boundary Layers: Observations, Models and Variability. Part 1: Modelling and Measurements’, Boundary-Layer Meteorol. 74, 19–54.
Derbyshire, S. H. and Holden, J. J.: 1994, ‘Llanthony 1994: Stable Boundary Layer Flow over a Valley’, Turbulence and Diffusion Note 259, Meteorological Office (APR).
Grant, A. L. M. and Mason, P. J.: 1990, ‘Observations of Boundary-Layer Structure over Complex Terrain’, Quart. J. Roy. Meteorol. Soc. 116, 159–186.
Holden, J. J.: 1998, ‘Stable Boundary Layer Flow over Hills and Valleys’, Ph.D. Thesis, University of Reading.
Jackson, P. S. and Hunt, J. C. R.: 1975, ‘Turbulent Wind Flow over a Low Hill’, Quart. J. Roy. Meteorol. Soc. 101, 929–955.
Kaimal, J. C. and Finnigan, J. J.: 1994, Atmospheric Boundary Layer Flows, Oxford University Press, 289 pp.
Lapworth, A. J. and Mason, P. J.: 1988, ‘The New Cardington Balloon-Bourne Turbulence Probe System’, J. Atmos. Oceanic Tech. 5, 699–714.
Mason, P. J.: 1987, ‘Diurnal Variations in Flow over a Succession of Ridges and Valleys’, Quart. J. Roy. Meteorol. Soc. 113, 1117–1140.
Nieuwstadt, F. T. M.: 1984, ‘The Turbulent Structure of the Stable, Nocturnal Boundary Layer’, J. Atmos. Sci. 41, 2202–2216.
Nieuwstadt, F. T. M.: 1985, ‘A Model for the Stationary, Stable Boundary Layer’, in J. C. R. Hunt (ed.), Proceedings of IMA Conference on Turbulence and Diffusion in Stable Environments, OUP, Cambridge, U.K., pp. 149–179.
Turner, J. S.: 1973, Buoyancy Effects in Fluid, Cambridge University Press, 368 pp.
Wood, N.: 1995, ‘The Onset of Separation in Neutral Turbulent Flow over Hills’, Boundary-Layer Meteorol. 76, 137–164.
Wood, N.: 1998, ‘Turbulent Fluxes in Complex Terrain, and the Effects of Static Stability’, in Proceedings of a Workshop Held at ECMWF on Orography, 10–12 November 1997, ECMWF, Reading, U.K., pp. 23–50.
Wood, N. and Mason, P. J.: 1993, ‘The Pressure Force Induced by Neutral, Turbulent-Flow over Hills’, Quart. J. Roy. Meteorol. Soc. 119, 1233–1267.
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Holden, J.J., Derbyshire, S.H. & Belcher, S.E. Tethered Balloon Observations Of The Nocturnal Stable Boundary Layer In A Valley. Boundary-Layer Meteorology 97, 1–24 (2000). https://doi.org/10.1023/A:1002628924673
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DOI: https://doi.org/10.1023/A:1002628924673