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Use of Mass Conservation and Critical Dividing Streamline concepts for Efficient Objective Analysis of Winds in Complex Terrain

F. L. LudwigSRI International, Menlo Park, California

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J. M. LivingstonSRI International, Menlo Park, California

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R. M. EndlichSRI International, Menlo Park, California

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Abstract

Observed winds and temperature profiles can be used to generate three-dimensional, mass-conserving wind fields that reflect topographical influences. The concept of critical dividing streamlines is used to define quasi-horizontal, flow-confining two-dimensional surfaces. Adjustment toward two-dimensional nondivergence on those surfaces forces flow around obstacles under stable conditions when some flow surfaces intersect higher terrain features. Unlike most mass-conserving wind models, the approach described here includes objective evaluation of the effects of atmospheric stability. Efficiency is achieved by casting the three-dimensional problem as several two-dimensional problems and by using an iterative scheme to adjust toward nondivergence. A 20 × 20 × 5 gridpoint analysis requires approximately 2 min on an IBM-AT personal computer.

Abstract

Observed winds and temperature profiles can be used to generate three-dimensional, mass-conserving wind fields that reflect topographical influences. The concept of critical dividing streamlines is used to define quasi-horizontal, flow-confining two-dimensional surfaces. Adjustment toward two-dimensional nondivergence on those surfaces forces flow around obstacles under stable conditions when some flow surfaces intersect higher terrain features. Unlike most mass-conserving wind models, the approach described here includes objective evaluation of the effects of atmospheric stability. Efficiency is achieved by casting the three-dimensional problem as several two-dimensional problems and by using an iterative scheme to adjust toward nondivergence. A 20 × 20 × 5 gridpoint analysis requires approximately 2 min on an IBM-AT personal computer.

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