Statistics of Scalar Fields in the Atmospheric Boundary Layer Based on Large-Eddy Simulations. Part II: Forced Convection
Forced convection in a quasi-steady atmospheric boundary layer is investigated based on a large-eddy simulation (LES) model. The performed simulations show that in the upper portion of the mixed layer the dimensionless (in terms of mixed layer scales) vertical gradients of temperature, humidity, and wind velocity depend on the dimensionless height z/z i and the Reech number Rn. The peak values of variances and covariances at the top of the mixed layer, scaled in terms of the interfacial scales, are functions of the interfacial Richardson number Ri. As a result expressions for the entrainment rates, in the case when the interfacial layer has a finite depth, and a condition for the presence of moistening or drying regimes in the mixed layer, are derived. Profiles of dimensionless scalar moments in the mixed layer are proposed to be expressed in terms of two empirical similarity functions F m and F i , dependent on dimensionless height z/z i , and the interfacial Richardson number Ri. The obtained similarity expressions adequately approximate the LES profiles of scalar statistics, and properly represent the impact of stability, shear, and entrainment. They are also consistent with the parameterization proposed for free convection in the first part of this paper.
KeywordsAtmospheric boundary layer Forced-convection Interfacial layer Entrainment Large-eddy simulations Similarity scales
Unable to display preview. Download preview PDF.
- Deardorff J.W., (1974a), ‘Three-Dimensional Numerical Study of the Height and Mean Structure of a Heated Planetary Boundary’. Boundary-Layer Meteorol. 7, 81–106Google Scholar
- Deardorff J.W., (1974b), ‘Three-Dimensional Numerical Study of Turbulence in an Entraining Mixed Layer’. Boundary-Layer Meteorol. 7, 199–226Google Scholar
- Garratt J.R., (1992), The Atmospheric Boundary Layer, Cambridge University Press, 316 pp.Google Scholar
- Lilly D. K. (2002), ‘Entrainment into Mixed Layers. Part I: Sharp-Edged and Smoothed Tops’. J. Atmos. Sci. 59, 3340–3361Google Scholar
- Mason P.J., (1992), ‘Large-Eddy Simulation of Dispersion in Convective Boundary Layer with Wind Shear’. Atmos. Environ. 26(9): 151–1571Google Scholar
- Moeng C.H., Sullivan P.P., (1994), ‘A Comparison of Shear and Buoyancy Driven Planetary Boundary Layer Flows’. J. Atmos. Sci. 51, 999–1022Google Scholar
- Otte M. J., Wyngaard J.C., (2000), ‘Stably Stratified Interfacial-layer Turbulence’. in 14th Symposium on Boundary Layer and Turbulence, American Meteorological Society, Aspen, pp. 74–75.Google Scholar
- Sorbjan Z., (2005), ‘Statistics of Scalar Fields in the Atmospheric Boundary Layer Based on Large-Eddy Simulations. Part I: Free convection’. Accepted to Boundary-Layer Meteorol.Google Scholar