An Application of the Dividing-Streamline Concept to the Stable Airflow over Mesoscale Mountains

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Abstract
Atmospheric stable airflow over a mesoscale mountain chain has been considered in order to provide an evaluation, based on isentropic analysis, of the base height of the upwind flow layer passing over the mountains. The trend of this height as a function of the Froude number suggests that in the real atmosphere the upwind influence is detectable at Froude number larger than 1.5. The empirically determined height is, on average, greater than that obtained by Sheppard's dividing-streamline formula, which could provide a lower limit. The wind shear produces a downward deflection of the streamlines, which can be simply accounted for as far as strong stratification cases are concerned. The three-dimensionality of the flow is discussed in order to assess the structure of the region below this dividing height. Abstract Atmospheric stable airflow over a mesoscale mountain chain has been considered in order to provide an evaluation, based on isentropic analysis, of the base height of the upwind flow layer passing over the mountains. The trend of this height as a function of the Froude number suggests that in the real atmosphere the upwind influence is detectable at Froude number larger than 1.5. The empirically determined height is, on average, greater than that obtained by Sheppard's dividing-streamline formula, which could provide a lower limit. The wind shear produces a downward deflection of the streamlines, which can be simply accounted for as far as strong stratification cases are concerned. The three-dimensionality of the flow is discussed in order to assess the structure of the region below this dividing height.

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