A Nocturnal Atmospheric Drainage Flow Simulation Investigating the Application of One-Dimensional Modeling and Current Turbulence Schemes

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  • 1 Department of Earth Sciences, Iowa State University, Ames, IA 50011
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Abstract

We developed a one-dimensional boundary layer model to simulate nocturnal atmospheric drainage flow on a simple forest-covered slope using canopy, soil and radiation parameterizations from previous studies along with turbulence simulation (from Mellor-Yamada) level three. A simulation of the drainage at Unit 19 of the ASCOT Geysers Project, 24 September 1980, is presented, from which we find that whatever horizontal flow-structure assumptions are made significantly affect the results through implied vertical advections. We recommend use of vertical-motion patterns obtained in relatively coarse two-dimensional simulations as a possible solution.

Turbulence as simulated develops significant anisotrophy. Careful simulation of turbulence structure will require some reexamination of present turbulence modeling techniques.

Nevertheless, using level three and assuming horizontal homogeneity, we were able to simulate well the mean profiles of wind and temperature at Unit 19 for one time when the ambient flow was light, minimizing the influence of the surrounding complex terrain. One-dimensional simulations will be valuable for fine-resolution tests of future turbulence schemes and other such parameterizations for complex-terrain application so long as due account is given to limitations such as those described in this work.

Abstract

We developed a one-dimensional boundary layer model to simulate nocturnal atmospheric drainage flow on a simple forest-covered slope using canopy, soil and radiation parameterizations from previous studies along with turbulence simulation (from Mellor-Yamada) level three. A simulation of the drainage at Unit 19 of the ASCOT Geysers Project, 24 September 1980, is presented, from which we find that whatever horizontal flow-structure assumptions are made significantly affect the results through implied vertical advections. We recommend use of vertical-motion patterns obtained in relatively coarse two-dimensional simulations as a possible solution.

Turbulence as simulated develops significant anisotrophy. Careful simulation of turbulence structure will require some reexamination of present turbulence modeling techniques.

Nevertheless, using level three and assuming horizontal homogeneity, we were able to simulate well the mean profiles of wind and temperature at Unit 19 for one time when the ambient flow was light, minimizing the influence of the surrounding complex terrain. One-dimensional simulations will be valuable for fine-resolution tests of future turbulence schemes and other such parameterizations for complex-terrain application so long as due account is given to limitations such as those described in this work.

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