Fetch- and Duration-Limited Nature of Surface Wave Growth inside Tropical Cyclones: With Applications to Air–Sea Exchange and Remote Sensing

Abstract

he 2D wavenumber spectra collected by an airborne scanning radar altimeter in hurricane hunter missions are used to investigate the fetch- and duration-limited nature of wave growth inside hurricanes. Despite the much more complex wind-forcing conditions, the dimensionless growth curves obtained with the wind-wave triplets (reference wind velocity, significant wave height, and dominant wave period) inside hurricanes, except near the eye region, are comparable to the reference similarity counterparts constructed with the wind-wave triplets collected in field experiments conducted under ideal quasi-steady fetch-limited conditions. In dimensionless terms, the youngest waves are in the back quarter of the hurricane. In the Northern Hemisphere, the dimensionless frequency decreases systematically counterclockwise (CCW), and the most mature waves are in the left-hand sector. Except for those waves near the eye region, the dominant wave phase speeds are about 0.32 to 0.71 times of the local wind speed, and they are proper wind seas. Based on the computation of the wind input or energy dissipation in the wave field, a conservative estimate of the air?sea energy exchange over the coverage area of a category one hurricane is about 5 TW. Formulas for the effective fetches and durations in the three hurricane sectors are derived from the data. Using these formulas together with the wave growth functions, the full set of wind-wave triplets can be calculated knowing only one of the three. These results may enhance the capability and scope of monitoring hurricanes from space.