The aerodynamics of the tall tower are important in minimizing imposed design forces. Across-wind motion (perpendicular to the direction of applied wind load) governs the behavior of the structure. Organized vortex shedding generates the highest forces levels. Vortex shedding is most organized (has the most adverse effects) with circular cross-sectional shapes, less organized with triangular shapes, and least organized with square shapes. The introduction of holes through the building cross-sections improves the behavior further. Variation of the structure’s cross-section along its height also acts to disorganize or disseminate vortex shedding. Strouhal numbers describe oscillating flow mechanisms and are based on the frequency of vortex shedding, shape geometry, and wind velocity. Strouhal numbers for common building shapes are shown below in parentheses.