What can Hurricane SAM (2021) tell us about ocean waves under tropical cyclones?

TL;DR

This study analyzes ocean wave data under Hurricane SAM (2021) using satellite, airborne, and in situ measurements, demonstrating the reliability of remote sensing in heavy rain conditions and exploring wave mechanisms in tropical cyclones.

Contribution

It provides a comprehensive validation of wave spectra measurements from multiple sources during a hurricane and investigates the impact of rain on remote sensing data quality.

Findings

Satellite and in situ wave spectra are consistent.

Rain affects radar cross section but not wave spectrum quality.

A trapped wave mechanism explains large wave heights in the cyclone.

Abstract

We investigate the ocean wave field under Hurricane SAM (2021). Whilst measurements of waves under Tropical Cyclones (TCs) are rare, an unusually large number of quality in situ and remote measurements are available in that case. First, we highlight the good consistency between the wave spectra provided by the Surface Waves Investigation and Monitoring (SWIM) instrument onboard the China-France Oceanography Satellite (CFOSAT), the in situ spectra measured by National Data Buoy Center (NDBC) buoys, and a saildrone. The impact of strong rains on SWIM spectra is then further investigated. We show that whereas the rain definitely affects the normalized radar cross section, both the innovative technology (beam rotating scanning geometry) and the post-processing processes applied to retrieve the 2D wave spectra ensure a good quality of the resulting wave spectra, even in heavy rain conditions. On this basis, the satellite, airborne and in situ observations are confronted to the analytical model proposed by Kudryavtsev et al (2015). We show that a trapped wave mechanism may be invoked to explain the large significant wave height observed in the right front quadrant of Hurricane SAM.