Directional Wave Organization Reflects Spectral Memory in Tropical Cyclones
R. Wyn Pauly, Hyodae Seo, Jacob R. Davis, Steven R. Jayne, and Carol Anne Clayson
Observations of spectral wave properties under tropical cyclones are commonly interpreted using contemporaneous environmental descriptors such as local wind speed, wind direction, storm-relative position, and storm intensity. However, surface waves evolve over finite adjustment timescales through wind input, dissipation, and nonlinear wave-wave interactions, suggesting that instantaneous forcing alone may not uniquely determine the wave state. Here, we combine North Atlantic multi-storm Spotter directional wave spectra with collocated COAMPS-TC atmospheric fields to quantify the first-order dependence of bulk and spectral wave properties on the local wind environment. Smooth, nonparametric baseline models are evaluated across independent storms to characterize the component of wave variability explained by the local wind environment, while residual variability is examined for systematic departures from a local equilibrium framework.
While local wind forcing explains much of the variability in significant wave height, peak frequency, and other bulk wave properties, residual variability remains among observations experiencing similar instantaneous forcing conditions. Among these otherwise similarly forced wave fields, differences in peak-frequency directional spreading coincide with differences in significant wave height and mean square slope. These results are consistent with the interpretation that directional organization reflects spectral memory arising from the finite, spectrally dependent adjustment of the wave spectrum toward a changing equilibrium.
The associated differences in mean square slope further indicate corresponding differences in short-wave roughness and high-frequency directional organization, with potentially important consequences for wave-supported stress and air-sea momentum transfer. Because these differences arise among wave fields subject to similar forcing, they represent a source of sea-state variability beyond that described by equilibrium-based bulk parameterizations. Together, these findings support a history-dependent description of tropical cyclone wave evolution in which spectral memory introduces an additional dimension of wave-state variability beyond that explained by instantaneous forcing.