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R. A. Pielke, M. Segal, R. T. McNider, and Y. Mahrer

Abstract

This paper examines two coordinate representations for slope flow models, one a rotation of the coordinate axes, the other a generalized vertical coordinate transformation. An analytic solution is developed in both representations for a uniform slope to examine the differences due to slightly different forms of a generalised hydrostatic equation. For the first transformation, velocity acclerations in the direction of the generalized vertical coordinate are ignored, while for the second transformation, velocity accelerations perpendicular to the terrain are neglected. Surprisingly, only the period of flow oscillation and not the mean strength of the slope flow was changed in using the first coordinate representation instead of the second. Only for slopes greater than 45° does the difference in periods between the two transformations 30%. Differences which may occur for nonuniform slopes, however, still need to be examined.

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M. Segal, J. L. Song, R. A. Pielke, J. F. W. Purdom, and Y. Mahrer

Abstract

This study presents scale analysis and numerical model evaluations of the impact of cloud shading on 1) the development of sea breeze and thermally induced upslope flows and 2) the generation of mesoscale circulations between cloudy areas adjacent to clear areas. Based on the assumption of modifications of solar and longwave radiation which are typical for some overcast conditions, it was found that the reduction in the first type of circulation is significant and most noticeable in the vertical velocities. In the second case, thermally induced circulations in favorable conditions appear to approach the typical intensity of the sea breeze.

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