Hurricane Boundary Layer Response to Idealized Combinations of Moderate Steering and Shear

Given the importance of storm motion, vertical wind shear, and vortex tilt on tropical cyclone (TC) processes, structure, and intensity, a common path in TC research involves the assignment of various background soundings with flow to idealized simulations. A subset of such research has focused specifically on structure and processes within the TC boundary layer (BL) in relation to storm motion, shear, and/or tilt. For instance, the superposition of a storm motion vector onto an axisymmetric vortex in a storm-relative frame of reference imparts Earth-relative asymmetries in the flow, which we expect would induce frictional forcing that is asymmetrically stronger to the right of motion in the Northern Hemisphere. Further, the ventilation effect of vertical wind shear and tilt has been tied to asymmetries in the overturning circulation of a TC, with the downshear or downtilt sector generally housing the deepest and strongest low-level radial inflow.

This work endeavors to improve our understanding of how the two disparate factors of storm motion and vertical wind shear combine to drive asymmetric structure in the TC BL. Idealized three-dimensional simulations in Cloud Model 1 will be used for this work, which allow for the adjustment of background steering and vertical wind shear from a background state of rest. Notably, this research highlights TC BL responses to the application of various background soundings with moderate, equal magnitudes of steering and deep-layer vertical wind shear that differ in the angle between steering and shear. The application of experimental background soundings occurs following a 60-hour spin-up period in a quiescent environment, at which point the TC has maximum mean-tangential winds of about 100 kt at 1.5 km elevation.