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J. Neumann and Y. Mahrer

Abstract

Estoque's model for the sea breeze is modified with respect to some essential and other, less essential, details. It is shown among other things that the accelerational terms in the equation for the vertical component of motion are important and should therefore be retained. In addition, the equation of continuity is retained in its original form in order to prevent violation of the mass conservation law. The new model is integrated numerically and the results presented. The results include horizontal and vertical winds, mass conservation, vertical components of vorticity, time hodographs, temperatures (including vertical profiles), vertical transfer of sensible heat, and wind stress at the surface. Particular attention is paid to the land breeze phase of the circulation which so far has received little attention in the published literature. Further, the sea breeze front is discussed in some detail.

The integration is carried out for three daily cycles setting out from an atmosphere at rest. The results for Days 2 and 3 as well as for the second part of Day 1 are in good agreement.

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J. Neumann and Y. Mahrer

Abstract

The axisymmetric sea and land breezes of circular islands are studied. First we show, from the equation of turbulent energy, that the marked horizontal convergence of the sea breeze intensifies the turbulence in the flow and that this conclusion affects the equations that model the turbulence. Next, the equations of motion are integrated numerically for two circular islands: a “large” island of radius 51.25 km and a “small” island of radius 26.25 km. The horizontal grid is 2.5 km and the vertical 100 m beginning from the top of a postulated constant-flux layer 25 m thick.

Large island. The sea-breeze front (SBF) is much better developed than in the case of a straight coast. In the first hours of the afternoon the low-level winds ahead of the front are nearly opposite in direction to those of the sea breeze behind the front. There is a strong horizontal convergence in advance of, and divergence behind, the front up to an altitude of 400–500 m; the reverse distribution is the case aloft, where the winds ahead of the surface position of the front depart from the picture of a countercirculation and blow in the same direction as the sea breeze near the surface. The maximum computed upward velocity occurs about the front and reaches 50 cm sec−1. The most surprising feature is the formation in the afternoon of an “eye” of downward velocities around the island center ahead of the front. By late afternoon, however, the island center becomes the center of upward motion. All the above events are connected with an instability developing about the SBF, including the evolution of a pressure low about the surface position of the front. This low deepens as the front moves inland. The land breezes are horizontally divergent with the largest speeds found over the sea.

Small island. The SBF reaches the center about 1300 local time so that little development can take place along the front. However, the upward velocities reach 150 cm sec−1 over the center.

In conclusion, it is pointed out that the most interesting features of the sea breeze occur well inland, whereas those of the land breeze occur well offshore.

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

Abstract

No abstract available.

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