The Dependence of Canyon Winds on Surface Cooling and External Forcing in Colorado's Front Range

Richard L. Coulter Argonne National Laboratory, Argonne, Illinois

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Paul Gudiksen Lawrence Livermore National Laboratory, Livermore, California

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Abstract

The atmospheric katabatic flow in the foothills of the Front Range of the Rocky Mountains has been monitored by a network of towers and sodars for several years as part of the ASCOT program. The dependence of the outflow from Coal Creek Canyon on surface cooling and channeling by winds above the canyon is explored by using three years of data from a portion of the network. The depth of the drainage flow and the height of the wind speed maximum were found to be largest at external wind speeds near 3 m s−1. For lighter winds aloft, the drainage depth, the height of the jet, and the drainage wind speed depend both on external wind speed and on the strength of the surface cooling. The magnitude of the near-surface temperature differences was also found to decrease with increasing surface cooling, possibly because of increasing turbulence caused by winds interacting with surface topography.

Abstract

The atmospheric katabatic flow in the foothills of the Front Range of the Rocky Mountains has been monitored by a network of towers and sodars for several years as part of the ASCOT program. The dependence of the outflow from Coal Creek Canyon on surface cooling and channeling by winds above the canyon is explored by using three years of data from a portion of the network. The depth of the drainage flow and the height of the wind speed maximum were found to be largest at external wind speeds near 3 m s−1. For lighter winds aloft, the drainage depth, the height of the jet, and the drainage wind speed depend both on external wind speed and on the strength of the surface cooling. The magnitude of the near-surface temperature differences was also found to decrease with increasing surface cooling, possibly because of increasing turbulence caused by winds interacting with surface topography.

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