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Steady, Neutral Planetary Boundary Layer Forced by a Horizontally Non-Uniform Flow

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  • 1 Laboratory for Atmospheric Research, University of Illinois, Urbana 61801
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Abstract

A method, which consists of accumulative applications of Newton's iterative algorithm in parameter space, is used to determine the three-dimensional flow of a steady, neutral, horizontally inhomogeneous planetary boundary layer (PBL) driven by an imposed rectilinear flow, with a large cross-wind shear, over a surface of uniform roughness. It is found for large Rossby number that the flow structure and dynamics in the region, say P, where the vorticity of the imposed flow is positive is qualitatively different from that in the region, say N, where it is negative. The differences are manifested in all major properties of the flow, namely, the horizontal velocity-vector holograph, the vertical velocity distribution, the height of the PBL, the surface cross-isobar angle, the eddy coefficient, the energetics and the vorticity dynamics. One explanation seems to be that while horizontal and vertical advection both contribute to a convergence of v momentum in region P (v being perpendicular to the imposed flow), the corresponding contribution to region N involves convergence for the former and an overcompensating divergence for the latter.

Abstract

A method, which consists of accumulative applications of Newton's iterative algorithm in parameter space, is used to determine the three-dimensional flow of a steady, neutral, horizontally inhomogeneous planetary boundary layer (PBL) driven by an imposed rectilinear flow, with a large cross-wind shear, over a surface of uniform roughness. It is found for large Rossby number that the flow structure and dynamics in the region, say P, where the vorticity of the imposed flow is positive is qualitatively different from that in the region, say N, where it is negative. The differences are manifested in all major properties of the flow, namely, the horizontal velocity-vector holograph, the vertical velocity distribution, the height of the PBL, the surface cross-isobar angle, the eddy coefficient, the energetics and the vorticity dynamics. One explanation seems to be that while horizontal and vertical advection both contribute to a convergence of v momentum in region P (v being perpendicular to the imposed flow), the corresponding contribution to region N involves convergence for the former and an overcompensating divergence for the latter.

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