Transformed Shoreline-following Horizontal Coordinates in a Mesoscale Model: A Sea Land-Breeze Case Study

Abstract

A hydrostatic and incompressible mesoscale model with transformed horizontal coordinates is presented. The model is applied to study the sea-land-breeze circulation over Río de La Plata. One of the new coordinates is shoreline-following and the other one is locally quasi-perpendicular to the first one. The original set of equations in the Cartesian coordinates is rewritten in the curvilinear coordinates. This transformation is useful provided that the curvilinear coordinates are close to being orthogonal. The horizontal domain covers 250 km ? 250 km, and the vertical domain is 2 km deep. To predict the sea?land-breeze circulation the model is integrated over 12 h. The forcing of the model is a cyclic perturbation of the surface temperature. The changes in the wind direction during the day are in good agreement with the observations from six weather stations in the region. The same program code is applied to uniform domains of different resolutions in order to test the coordinate transformation. Results show that the predictions based upon the variable-resolution version resemble ones obtained using high uniform resolution but consume only one-fourth the computer time needed by the latter. Comparison of the vertical velocity patterns predicted by the model to the cumulus clouds distribution observed from satellite images show a very good agreement too. We believe that all these results justify the use of the coordinate transformation in this type of model, although further verifications are needed in order to draw more definitive conclusions.