Topographic Effects on the Tropical Land and Sea Breeze

The effect of an inland plateau on the tropical sea breeze is considered in terms of idealized numerical experiments, with a particular emphasis on offshore effects. The sea breeze is modeled as the response to an oscillating interior heat source over land. The parameter space for the calculations is defined by a nondimensional wind speed, a scaled plateau height, and the nondimensional heating amplitude. The experiments show that the inland plateau tends to significantly strengthen the land-breeze part of the circulation, as compared to the case without terrain. The strengthening of the land breeze is tied to blocking of the sea-breeze density current during the warm phase of the cycle. The blocked sea breeze produces a pool of relatively cold, stagnant air at the base of the plateau, which in turn produces a stronger land-breeze density current the following morning. Experiments show that the strength of the land breeze increases with the terrain height, at least for moderate values of the height. For very large terrain, the sea breeze is apparently blocked entirely, and further increases in terrain height lead to only small changes in land-breeze intensity and propagation. Details of the dynamics are described in terms of the transition from linear to nonlinear heating amplitudes, as well as for cases with and without background winds. The results show that for the present experiments, significant offshore effects are tied to nonlinear frontal propagation, as opposed to quasi-linear wave features.