Vertical Velocity Generated Over Non-Homogeneous Rough Terrain, Theory and Subgrid-Scale Parameterization

Abstract

A systematic evaluation of vertical velocities associated with stratified atmospheric flows over non-homogeneous terrains apparently has not been reported in the literature. This study approaches the problem numerically and analytically. A non-linear model evaluates the range of the parameters for validity of the linear theory. Simple analytical theory estimates the role played by the relevant parameters. Results indicate that, when the transition in surface roughness is gradual between a smooth and a rough surface, the perturbation of the vertical velocity has the same horizontal scale as the perturbing source. The nature of the perturbation depends on the product between the horizontal scale of the rough patch and the Scorer parameter of the ambient atmosphere; i.e. very small values of this product (weakly stratified atmosphere) gives a wave trapped around the top of the stress layer, while values of the order of unity give a non-hydrostatic gravity wave which propagates away from the top of the stress layer. Values larger than unity yield a propagating hydrostatic wave. When the transition in surface roughness is abrupt, the wave is nonhydrostatic with a horizontal and vertical wave number equal to the ambient Scorer parameter. When the product between the horizontal width of the rough patch and the Scorer parameter is large, there is no significant interference between the wave upstream and the wave downstream of the rough patch; the two waves are of the same nature and amplitude, but opposite sign. When this product is small, however, the wave upstream interferes destructively with the wave downstream, i.e., the amplitude of the resulting wave is accordingly reduced.

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Document Details

Document Type
Technical Report
Publication Date
Feb 02, 1990
Accession Number
ADA244253

Entities

People

  • A. Guerrini
  • G. A. Dalu
  • M. Segal
  • R. A. Pielke
  • T. J. Lee

Organizations

  • Colorado State University

Tags

Communities of Interest

  • Air Platforms
  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Amplitude
  • Atmospheric Motion
  • Atmospheric Sciences
  • Boundary Layer
  • Convection
  • Equations
  • Far Field
  • Flow
  • Intensity
  • Layers
  • Near Field
  • Simulations
  • Surface Roughness
  • Turbulence
  • Two Dimensional
  • Urban Areas
  • Wind

Readers

  • Calculus or Mathematical Analysis
  • Fluid Mechanics and Fluid Dynamics.
  • Ocean-Atmosphere Mesoscale Modeling, Data Assimilation, and Flux Boundary Layers