Large-Eddy Simulations of the Tropical Cyclone boundary layer at landfall in an idealized urban environment

TC winds impinge perpendicu-larly to the urbanized coastline. Numerical experiments show that buildings generate distinct, intricate flow patterns that vary significantly as the city structure is varied. Urban IBCs produce much stronger turbulent kinetic energy than is pro-duced by conventional surface parameterizations.

Strong effective eddy viscosity due to resolved eddy mixing is displayed in the wake of buildings within the urban canopy, while deep and enhanced effective eddy viscosity is present downstream. Such effects are not seen in a comparison LES using a simple surface parameterization with high roughness values. Wind tunneling effects in streamwise canyons enhance pedestrian-level winds well beyond what is possible without buildings.

In the arena of regional mesoscale modeling, this type of LES framework with IBCs can be used to improve parameters in surface and bound-ary layer schemes to more accurately represent the drag coefficient and the eddy viscosity in landfalling TC boundary layers. SIGNIFICANCE STATEMENT: This is among the first large-eddy simulation model studies to examine the impacts of tropical cyclone-like winds around explicitly resolved buildings.

This work is a step forward in bridging the gap between engineering studies that use computational fluid dynamics models or laboratory experiments for flow through cities and mesoscale model simulations of landfalling tropical cyclones that use surface parameterizations specialized for urban land use.