High-Wavenumber Eddies in the Eyewall of Simulated Hurricane Earl (2010): Structure, Evolution, and Impact on Near-Surface Strong Winds

Abstract This study examines the structure, evolution, and impacts of high-wavenumber eddies (HWEs; azimuthal wavenumber ≥ 12) at the inner edge of a tropical cyclone (TC) eyewall by analyzing a subkilometer numerical simulation of Hurricane Earl (2010). These eddies, with horizontal scales from approximately one to several kilometers, are predominantly concentrated within an annulus of high potential vorticity (PV) in the lower troposphere. Their activity peaks during rapid intensification, particularly when the eyewall PV ring is thin and hollow. The eddies preferentially emerge in the downshear-left quadrant and propagate azimuthally, reaching their maximum intensity in the upshear quadrants. As the eddies intensify, their associated flow reorganizes adjacent radial vorticity anomalies, originally oriented azimuthally, into radially oriented horizontal roll vortices. These roll vortices exhibit a consistent phase relationship relative to the HWEs, with negative (positive) radial vorticity anomalies leading (lagging) the cyclonic eddies by approximately one-quarter wavelength. Notably, the advection of hydrometers by enhanced radial inflows, immediately downstream of the intensified cyclonic eddies and collocated with the horizontal roll vortices, is the primary cause of high-reflectivity filaments along the eyewall inner edge, features that have been observed by aircraft and ground-based radars. Locally intensified near-surface winds occur slightly upstream of these filaments and radially outward from the cyclonic eddies. The radially inward vorticity flux due to eddy-component flows and local eddy-component pressure gradient force, rather than vertical momentum transport by downdrafts, are the main drivers of eddy-component tangential flow strengthening and near-surface wind amplification through superposition onto the intense background eyewall circulation. Significance Statement Filaments of high radar reflectivity extending from the inner edge of the eyewall into the eye are frequently observed in strong TCs. These finger-like radar echoes are associated with intense surface wind gusts capable of causing severe wind damage during landfall. However, their formation timing, location, and underlying mechanism remain poorly understood. This modeling study addresses these questions and provides new insights into the genesis of these finger-like radar echoes, also referred to as high-wavenumber eyewall eddies. These findings have implications for improving nowcasting of strong near-surface winds in the eyewall.