Editorial Type:
Article
Article Type:
Research Article

An Evaluation of the Scale at which Topographical Features Affect the Convective Boundary Layer Using Large Eddy Simulations

S. G. Gopalakrishnan Center for Environmental Prediction, Department of Environmental Sciences, Cook College, Rutgers–The State University, New Brunswick, New Jersey

Search for other papers by S. G. Gopalakrishnan in
Current site
Google Scholar
PubMed Close
,
Somnath Baidya Roy Center for Environmental Prediction, Department of Environmental Sciences, Cook College, Rutgers–The State University, New Brunswick, New Jersey

Search for other papers by Somnath Baidya Roy in
Current site
Google Scholar
PubMed Close
, and
Roni Avissar Center for Environmental Prediction, Department of Environmental Sciences, Cook College, Rutgers–The State University, New Brunswick, New Jersey

Search for other papers by Roni Avissar in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Jan 2000
DOI:
https://doi.org/10.1175/1520-0469(2000)057<0334:AEOTSA>2.0.CO;2
Page(s):
334–351
Restricted access

Abstract

The major objective of this study was to evaluate at which scale topography starts to significantly affect the mean characteristics and structure of turbulence in the convective boundary layer (CBL). The large eddy simulation option of the Regional Atmospheric Modeling System developed at Colorado State University was used for that purpose. It is found that turbulence is nonlinearly dependent on the scale of the topographical features. At a horizontal length scale of less than about 5 km, topography has very little impact on the mean properties of the CBL, even with hills as high as 30% of the height of the CBL. However, it has a significant impact on the organization of the eddies. At larger horizontal scales, topographical features as small as about 10% of the height of the CBL have some effect on the mean characteristics of the CBL. In particular, a pronounced impact on the “dispersion” statistics (i.e., horizontal and vertical velocity variances and higher moments) is noticed. Furthermore, the mean turbulence kinetic energy profile depicts two maxima, one near the ground surface and one near the top of the CBL, corresponding to the strong horizontal flow that develops near the ground surface and the return flow at the top of the CBL resulting from the organization of eddies into rolls. The larger the sensible heat flux fueling the CBL at the ground surface, the less important this impact is. It is concluded that in a very irregular terrain, where topography presents a vertical scale of at least 200–400 m, and a horizontal scale larger than about 5 km, CBL parameterizations of turbulence currently employed in mesoscale and large-scale atmospheric models (e.g., general circulation models), as well as in dispersion models, need to be improved.

Corresponding author address: Prof. Roni Avissar, Dept. of Environmental Sciences, Cook College, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901-8551.

Abstract

The major objective of this study was to evaluate at which scale topography starts to significantly affect the mean characteristics and structure of turbulence in the convective boundary layer (CBL). The large eddy simulation option of the Regional Atmospheric Modeling System developed at Colorado State University was used for that purpose. It is found that turbulence is nonlinearly dependent on the scale of the topographical features. At a horizontal length scale of less than about 5 km, topography has very little impact on the mean properties of the CBL, even with hills as high as 30% of the height of the CBL. However, it has a significant impact on the organization of the eddies. At larger horizontal scales, topographical features as small as about 10% of the height of the CBL have some effect on the mean characteristics of the CBL. In particular, a pronounced impact on the “dispersion” statistics (i.e., horizontal and vertical velocity variances and higher moments) is noticed. Furthermore, the mean turbulence kinetic energy profile depicts two maxima, one near the ground surface and one near the top of the CBL, corresponding to the strong horizontal flow that develops near the ground surface and the return flow at the top of the CBL resulting from the organization of eddies into rolls. The larger the sensible heat flux fueling the CBL at the ground surface, the less important this impact is. It is concluded that in a very irregular terrain, where topography presents a vertical scale of at least 200–400 m, and a horizontal scale larger than about 5 km, CBL parameterizations of turbulence currently employed in mesoscale and large-scale atmospheric models (e.g., general circulation models), as well as in dispersion models, need to be improved.

Corresponding author address: Prof. Roni Avissar, Dept. of Environmental Sciences, Cook College, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901-8551.

Save
Cover Journal of the Atmospheric Sciences
Journal of the Atmospheric Sciences

  • André, J. C., P. Bougeault, and J. P. Goutorbe, 1990: Regional estimates of heat and evaporation fluxes over non-homogeneous terrain. Examples from the HAPEX-MOBILHY programme. Bound.-Layer Meteor.,50, 77–108.

  • Avissar, R., and R. A. Pielke, 1989: A parameterization of heterogeneous land surfaces for atmospheric numerical models and its impact on regional meteorology. Mon. Wea. Rev.,117, 2113–2136.

  • ——, and F. Chen, 1993: Development and analysis of prognostic equations for mesoscale kinetic energy and mesoscale (subgrid scale) fluxes for large-scale atmospheric models. J. Atmos. Sci.,50, 3751–3774.

  • ——, and Y. Liu, 1996: Sensitivity of shallow convective precipitation induced by land surface heterogeneities to dynamical and cloud microphysical parameters. J. Geophys. Res.,101, 7477–7497.

  • ——, and T. Schmidt, 1998: An evaluation of the scale at which ground-surface heat flux patchiness affects the convective boundary layer using large-eddy simulations. J. Atmos. Sci.,55, 2666–2689.

  • ——, E. W. Eloranta, K. Gurer, and G. J. Tripoli, 1998: An evaluation of the large-eddy simulation option of the regional atmospheric modeling system in simulating a convective boundary layer: A FIFE case study. J. Atmos. Sci.,55, 1109–1130.

  • Baidya Roy, S., and R. Avissar, 2000: Scales of response of the convective boundary layer to land-surface heterogeneity. Geophys. Res. Lett., in press.

  • Chen, F., and R. Avissar, 1994: Impact of land-surface moisture variability on local shallow convective cumulus and precipitation in large-scale models. J. Appl. Meteor.,33, 1382–1401.

  • Clark, T. L., 1977: A small-scale dynamic model using a terrain following coordinate transformation. J. Comput. Phys.,24, 186–215.

  • Deardorff, J. W., 1972: Numerical investigation of neutral and unstable planetary boundary layers. J. Atmos. Sci.,29, 91–115.

  • ——, 1980: Stratocumulus-capped mixed layers derived from a three-dimensional model. Bound.-Layer Meteor.,18, 495–527.

  • Gal-Chen, T., and R. C. J. Somerville, 1975: On the use of coordinate transformation for the solution of the Navier–Stokes equations. J. Comput. Phys.,17, 209–228.

  • Gopalakrishnan, S. G., and R. Avissar, 2000: An LES study of the impacts of land surface heterogeneity on dispersion in the convective boundary layer. J. Atmos. Sci.,56, 352–371.

  • Hadfield, M. G., W. R. Cotton, and R. A. Pielke, 1991a: Large-eddy simulations of thermally forced circulation in the convective boundary layer. Part I: A small-scale circulation with zero wind. Bound.-Layer Meteor.,57, 79–114.

  • ——, ——, and ——, 1991b: Large-eddy simulations of thermally forced circulation in the convective boundary layer. Part II: The effect of changes in wavelength and wind speed. Bound.-Layer Meteor.,58, 307–327.

  • Hechtel, L. M., C. H. Moeng, and R. B. Stull, 1990: The effects of nonhomogeneous surface fluxes on the convective boundary layer: A case study using large-eddy simulation. J. Atmos. Sci.,47, 1721–1741.

  • Krettenauer, K., and U. Schumann, 1989: Direct numerical simulation of thermal convection over a wavy surface. Meteor. Atmos. Phys.,41, 165–179.

  • Lamb, R. G., 1984: Diffusion in the convective boundary layer. Atmospheric Turbulence and Air Pollution Modeling, F. T. M. Nieuwstdat and H. van Dop, Eds., D. Reidel, 69–106.

  • Louis, J. F., 1979: A parametric model of vertical eddy fluxes in the atmosphere. Bound.-Layer Meteor.,17, 187–202.

  • Luhar, A. K., and R. E. Britter, 1989: A random walk model for dispersion in inhomogeneous turbulence in a convective boundary layer. Atmos. Environ.,23, 1911–1924.

  • McNider, R. T., M. D. Moran, and R. A. Pielke, 1988: Influence of diurnal and inertial boundary layer oscillations on long-range dispersion. Atmos. Environ.,22, 2445–2462.

  • Moeng, C. H., 1984: A large-eddy-simulation model for the study of planetary boundary-layer turbulence. J. Atmos. Sci.,41, 2052–2062.

  • Ookouchi, Y., M. Segal, R. C. Kessler, and R. A. Pielke, 1984: Evaluation of soil moisture effects on the generation and modification of mesoscale circulations. Mon. Wea. Rev.,112, 2281–2292.

  • Pielke, R. A., G. A. Dalu, J. S. Snook, T. J. Lee, and T. G. F. Kittel, 1991: Nonlinear influence of mesoscale land use on weather and climate. J. Climate,4, 1053–1069.

  • ——, and Coauthors, 1992: A comprehensive meteorological modeling system—RAMS. Meteor. Atmos. Phys.,49, 69–91.

  • Sawford, B. L., and F. M. Guest, 1987: Lagrangian stochastic analysis of flux gradient relationships in the convective boundary layer. J. Atmos. Sci.,44, 1152–1165.

  • Segal, M., and R. W. Arritt, 1992: Nonclassical mesoscale circulations caused by surface sensible heat-flux gradients. Bull. Amer. Meteor. Soc.,73, 1593–1604.

  • ——, R. Avissar, M. C. McCumber, and R. A. Pielke, 1988: Evaluation of vegetation effects on the generation and modification of mesoscale circulations. J. Atmos. Sci.,45, 2268–2292.

  • Shen, S., and M. Y. Leclerc, 1995: How large must surface inhomogeneities be before they influence the convective boundary layer structure? A case study. Quart. J. Roy. Meteor. Soc.,121, 1209–1228.

  • Tripoli, G. J., and W. R. Cotton, 1982: The Colorado State University Three-Dimensional Cloud/Mesoscale Model-1982. Part 1: General theoretical framework and sensitivity experiments. J. Rech. Atmos.,16, 185–219.

  • Walko, R. L., W. R. Cotton, and R. A. Pielke, 1992: Large-eddy simulations of the effects of hilly terrain on the convective boundary layer. Bound.-Layer Meteor.,58, 133–150.

  • Willis, G. E., and J. W. Deardorff, 1978: A laboratory study of dispersion from an elevated source within a modeled convective boundary layer. Atmos. Environ.,12, 1305–1311.

  • ——, and ——, 1981: A laboratory study of dispersion from a source in the middle of the convective boundary layer. Atmos. Environ.,15, 109–117.

  • Young, G. S., 1988: Turbulence structure of the convective boundary layer. Part II: Phoenix 78 aircraft observations of thermals and their environment. J. Atmos. Sci.,45, 727–735.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 295 61 7
PDF Downloads 143 43 6