Modeling rain-induced effects on boundary-layer wind field of tropical cyclones

摘要

Despite the significant impacts of heavy rainfall on the tropical cyclone intensity due to the transfer of horizontal momentum between air and raindrops, the comprehensive modeling of rain-induced effects on the boundary-layer wind field remains a challenge. The wind shear zone developed surrounding the falling precipitation results in complicated dynamic interactions between the wind and rain fields. The solution of dynamically coupled, intensively interactive wind and rain fields may be achieved using high-fidelity air-water interaction simulations but needs extremely high computational costs. To consider the wind-rain interactions with a first-order approximation, the fully-coupled dynamic system governing the raindrop motion and the wind field has been simplified herein to a weakly-coupled one represented by aerodynamic drag force. The drag-induced horizontal momentum transfer is integrated into the governing equations of the linear, height-resolving wind field, and an analytical model is accordingly developed to effectively consider the rain-induced effects on the boundary-layer winds of tropical cyclones. The results generated by the present model are consistent with the field measurements. It has been demonstrated that, while the wind speed can be either accelerated or decelerated depending on the location in the tropical cyclones and the rain parameters (e.g., rain rate, relative motion between the air and raindrops, drag coefficient and raindrop size distribution), the rain-induced effects on the boundary-layer wind directions (and hence the inflow angle) also have important significance on the tropical cyclone wind hazard on tall buildings and other structures. Due to its simplicity and high computational efficiency, the proposed model could be easily implemented in the risk assessments for tropical-cyclone wind hazards in engineering applications.