Evaluation of the Rankine vortex model for estimating near-surface tornadic wind fields in engineering applications

This study evaluates the ability of the modified Rankine vortex model, which is widely used to represent tornado-like vortices, to approximate a realistic tornado-like vortex generated within a high-resolution CM1 simulation. Horizontal wind fields at 10 m AGL were extracted from the CM1 simulation and averaged over multiple time windows to examine the influence of temporal averaging on peak wind speeds. The results show that 3-s averaging, although commonly used in engineering practice, can smooth short-lived transient flow structures and may underestimate instantaneous peak wind speeds. The CM1 wind field was then examined to determine the best-matched parameters of the Rankine vortex model. Separate decay exponents were applied inside and outside the vortex core, and a radially decaying translational velocity was incorporated. These modifications improved the near-surface wind field representation, particularly near the vortex core. Larger discrepancies were observed on the left side of the vortex, where complex asymmetric flow structures were not fully captured by the idealized Rankine vortex. Treefall patterns were simulated using different critical wind speeds, and the modified Rankine vortex produced results broadly comparable to those from the CM1 vortex. The findings of this study suggest that the Rankine vortex model, when applied with carefully selected best-matched parameters and combined with treefall modeling, could provide a practical framework for estimating near-surface tornado wind characteristics in engineering applications. Future work will examine additional cases to further assess the performance of the model under a wider range of tornado-like flow conditions.