Editorial Type:
Article
Article Type:
Research Article

An Evaluation of the Scale at which Ground-Surface Heat Flux Patchiness Affects the Convective Boundary Layer Using Large-Eddy Simulations

Roni Avissar Department of Environmental Sciences, Rutgers University, New Brunswick, New Jersey

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Tatyana Schmidt Department of Environmental Sciences, Rutgers University, New Brunswick, New Jersey

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Print Publication:
01 Aug 1998
DOI:
https://doi.org/10.1175/1520-0469(1998)055<2666:AEOTSA>2.0.CO;2
Page(s):
2666–2689
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Abstract

The effects on the convective boundary layer (CBL) of surface heterogeneities produced by surface sensible heat flux waves with different means, amplitudes, and wavelengths were investigated here. The major objective of this study was to evaluate at which scale surface heterogeneity starts to significantly affect the heat fluxes in the CBL. The large-eddy simulation option of the Regional Atmospheric Modeling System developed at Colorado State University was used for that purpose. Avissar et al. evaluated this model against observations and demonstrated its reliability. It appears that the impact of amplitude and wavelength of a heat wave is nonlinearly dependent upon the mean heating rate. The circulations (or rolls) resulting from surface heterogeneity are strong when the amplitude and the wavelength of the heat wave are large, especially at low mean heating rate. In that case the profiles of horizontally averaged variables are quite strongly modified in the CBL. The potential temperature is not constant with elevation, and the sensible heat flux considerably departs from the linear variation with height obtained in a typical CBL that develops over a homogeneous domain. 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. In a dry atmosphere, a weak background wind of 2.5 m s−1 is strong enough to considerably reduce the impact of ground-surface heterogeneity on the CBL. A moderate background wind of 5 m s−1 virtually eliminates all impacts that could potentially be produced in realistic landscapes. Water vapor does not significantly affect the CBL. However, the formation of rolls at preferential locations within the heterogeneous domain results in “pockets” of high moisture concentration, which have a strong potential for clouds formation. Such clouds may not form over homogeneous domains where moisture is more uniformly distributed, and the CBL is not as high as in heterogeneous domains. From this study, it can be concluded that as long as the “patchiness” of the landscape has a characteristic length scale smaller than about 5–10 km (even without background wind), the “mosaic of tiles” type of land surface scheme suggested by Avissar and Pielke can be applied to represent the land surface in atmospheric models. At larger scales, the impact of landscape heterogeneity may be significant, especially when the atmosphere is humid. Therefore, this study supports previous estimates, which were based on theoretical analyses.

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

Abstract

The effects on the convective boundary layer (CBL) of surface heterogeneities produced by surface sensible heat flux waves with different means, amplitudes, and wavelengths were investigated here. The major objective of this study was to evaluate at which scale surface heterogeneity starts to significantly affect the heat fluxes in the CBL. The large-eddy simulation option of the Regional Atmospheric Modeling System developed at Colorado State University was used for that purpose. Avissar et al. evaluated this model against observations and demonstrated its reliability. It appears that the impact of amplitude and wavelength of a heat wave is nonlinearly dependent upon the mean heating rate. The circulations (or rolls) resulting from surface heterogeneity are strong when the amplitude and the wavelength of the heat wave are large, especially at low mean heating rate. In that case the profiles of horizontally averaged variables are quite strongly modified in the CBL. The potential temperature is not constant with elevation, and the sensible heat flux considerably departs from the linear variation with height obtained in a typical CBL that develops over a homogeneous domain. 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. In a dry atmosphere, a weak background wind of 2.5 m s−1 is strong enough to considerably reduce the impact of ground-surface heterogeneity on the CBL. A moderate background wind of 5 m s−1 virtually eliminates all impacts that could potentially be produced in realistic landscapes. Water vapor does not significantly affect the CBL. However, the formation of rolls at preferential locations within the heterogeneous domain results in “pockets” of high moisture concentration, which have a strong potential for clouds formation. Such clouds may not form over homogeneous domains where moisture is more uniformly distributed, and the CBL is not as high as in heterogeneous domains. From this study, it can be concluded that as long as the “patchiness” of the landscape has a characteristic length scale smaller than about 5–10 km (even without background wind), the “mosaic of tiles” type of land surface scheme suggested by Avissar and Pielke can be applied to represent the land surface in atmospheric models. At larger scales, the impact of landscape heterogeneity may be significant, especially when the atmosphere is humid. Therefore, this study supports previous estimates, which were based on theoretical analyses.

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

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  • 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.

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

  • Businger, J. A., J. C. Wyngaard, Y. Izumi, and E. F. Bradley, 1971: Flux-profile relationships in the atmospheric surface layer. J. Atmos. Sci.,28, 181–189.

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

  • ——, and ——, 1994b: The impact of land-surface wetness heterogeneity on mesoscale heat fluxes. J. Appl. Meteor.,33, 1323–1340.

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

  • Dalu, G. A., R. A. Pielke, R. Avissar, G. Kallos, M. Baldi, and A. Guerrini, 1991: Linear impact of thermal inhomogeneities on mesoscale atmospheric flow with zero synoptic wind. Ann. Geophys.,9, 641–647.

  • Deardorff, J. W., 1974: Three-dimensional numerical study of the height and mean structure of a heated planetary boundary layer. Bound.-Layer Meteor.,7, 81–106.

  • ——, 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.

  • Hadfield, M. G., W. R. Cotton, and R. A. Pielke, 1991a: Large-eddy simulations of thermally forced circulations 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 circulations 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.

  • Lynn, B. H., F. Abramopoulos, and R. Avissar, 1995: Using similarity theory to parameterize mesoscale heat fluxes generated by subgrid-scale landscape discontinuities in GCMs. J. Climate,8, 932–951.

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

  • ——, and J. C. Wyngaard, 1984: Statistics of conservative scalars in the convective boundary layer. J. Atmos. Sci.,41, 3161–3169.

  • Oocouchi, 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.

  • Schmidt, H., and U. Schumann, 1989: Coherent structure of the convective boundary layer derived from large-eddy simulations. J. Fluid Mech.,200, 511–562.

  • 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.

  • Stull, R., 1988: An Introduction to Boundary Layer Meteorology. Kluwer Academic Publishers, 666 pp.

  • Tripoli, G. J., and W. R. Cotton, 1982: The Colorado State University Three-Dimensional Cloud/Mesoscale Model—1982. Part I: 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.

  • 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.

  • Zeng, X., and R. A. Pielke, 1995: Landscape-induced atmospheric flow and its parameterization in large-scale numerical models. J. Climate,8, 1156–1176.

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