Boundary-Layer Meteorology

, Volume 129, Issue 2, pp 269–287 | Cite as

The Effect of Surface Heating on Hill-Induced Flow Separation

  • Huw W. Lewis
  • Stephen D. Mobbs
  • Simon B. Vosper
  • Andy R. Brown
Original Paper

Abstract

A series of two-dimensional mixing length model simulations of boundary-layer flow over idealised ridges of varying steepness are conducted to investigate the effect of surface heating on flow separation. The relatively simple numerical approach used permits characterisation of the influence of heating for a variety of initial conditions and parameter values. For steep terrain, increased surface heating is shown to enhance the strength and extent of hill-induced separation. For more moderate terrain, a critical heating strength is required for a given hill width and background flow speed before separation is initiated. Sensitivity tests show the results to be insensitive to model parameters or the choice of mixing length. The results are accounted for using a scaling analysis in terms of a non-dimensional stability parameter.

Keywords

Boundary layer Convection Hills 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Allen T, Brown AR (2005) Modelling of turbulent form drag in convective conditions. Boundary-Layer Meteorol 118: 421–429CrossRefGoogle Scholar
  2. Arya SPS, Capuano ME, Fagen LC (1987) Some fluid modelling studies of flow and dispersion over two-dimensional low hills. Atmos Env 21: 753–764CrossRefGoogle Scholar
  3. Brown AR, Wood N (2003) Properties and parameterization of the stable boundary layer over moderate topography. J Atmos Sci 60: 2797–2808CrossRefGoogle Scholar
  4. Coppin PA, Bradley EF, Finnigan JJ (1994) Measurements of flow over an elongated ridge and its thermal stability dependence: the mean field. Boundary-Layer Meteorol 69: 173–199CrossRefGoogle Scholar
  5. Crook NA, Tucker DF (2005) Flow over heated terrain. Part I: Linear theory and idealised numerical simulations. Mon Wea Rev 133: 2552–2564Google Scholar
  6. Doorschot J, Raderschall N, Lehning M (2001) Measurements and one-dimensional model calculations of snow transport over a mountain ridge. Ann Glaciol 32: 153–158CrossRefGoogle Scholar
  7. Dörnbrack A, Schumann U (1993) Numerical simulation of turbulent convective flow over wavy terrain. Boundary-Layer Meteorol 65: 323–355Google Scholar
  8. Gopalakrishnan SG, Badia Roy S, Avissar A (2000) An evaluation of the scale at which topographical features affect the convective boundary layer using Large Eddy Simulations. J Atmos Sci 57: 334–351CrossRefGoogle Scholar
  9. Grant ALM, Mason PJ (1990) Observations of boundary-layer structure over complex terrain. Quart J Roy Meteorol Soc 116: 159–186CrossRefGoogle Scholar
  10. Kaimal JC, Finnigan JJ (1994) Atmospheric boundary-layer flows: their structure and measurement. Oxford University Press, U.K., 289 ppGoogle Scholar
  11. Lewis HW, Mobbs SD, Lehning M (2008) Observations of cross-ridge flows across steep terrain. Quart J Roy Meteorol Soc 134: 801–816CrossRefGoogle Scholar
  12. Mason PJ (1987) Diurnal variations in flow over a succession of ridges and valleys. Quart J Roy Meteorol Soc 113: 1117–1140CrossRefGoogle Scholar
  13. Mason PJ, King JC (1984) Atmospheric flow over a succession of nearly two-dimensional ridges and valleys. Quart J Roy Meteorol Soc 110: 821–845CrossRefGoogle Scholar
  14. Ross AN (2008) Large-eddy simulations of flow over forested ridges. Boundary-Layer Meteorol 128: 59–76CrossRefGoogle Scholar
  15. Scorer RS (1955) Theory of airflow over mountains: IV—separation of flow from the surface. Quart J Roy Meteorol Soc 81: 340–419CrossRefGoogle Scholar
  16. Taylor PA (1977) Numerical studies of neutrally stratified planetary boundary-layer flow above gentle topography. Boundary-Layer Meteorol 12: 37–60CrossRefGoogle Scholar
  17. Tian W, Parker DP (2002) Two-dimensional simulation of orographic effects on mesoscale boundary-layer convection. Quart J Roy Meteorol Soc 128: 1929–1952CrossRefGoogle Scholar
  18. Walko RL, Cotton WR, Pielke RA (1992) Large-eddy simulations of the effects of hilly terrain on the convective boundary layer. Boundary-Layer Meteorol 58: 133–150CrossRefGoogle Scholar
  19. Whiteman CD (1990) Observations of thermally developed wind. In: Blumen W (eds) Atmospheric processes over complex terrain, meteorological monographs, vol 23. American Meteorological Society, Boston, pp 5–42Google Scholar
  20. Wood N (1995) The onset of separation in neutral, turbulent flow over hills. Boundary-Layer Meteorol 76: 137–164CrossRefGoogle Scholar
  21. Wood N, Mason P (1993) The pressure force induced by neutral, turbulent flow over hills. Quart J Roy Meteorol Soc 119: 1233–1267CrossRefGoogle Scholar

Copyright information

© British Crown Copyright 2008, the Met Office, UK 2008

Authors and Affiliations

  • Huw W. Lewis
    • 1
    • 2
  • Stephen D. Mobbs
    • 1
  • Simon B. Vosper
    • 2
  • Andy R. Brown
    • 2
  1. 1.Institute for Atmospheric ScienceUniversity of LeedsLeedsUK
  2. 2.Met OfficeExeterUK

Personalised recommendations