CoAuthors

Fabrice Ardhuin ((Laboratoire d'Océanographie Physique et Spatiale (LOPS), University of Brest, CNRS, IUEM, Brest, France); Annabelle Ollivier (CLS Group (Collecte Localisation Satellites), , France); Alejandro Bohe (Centre National d'Etudes Spatiales (CNES), France)

Recent altimeter retracking (e.g. Tourain et al. 2021) and filtering methods (Quilfen et al. 2019) have considerably reduced the noise level in estimates of the significant wave height, allowing to study smaller scale processes. Previous studies on the along-track variations of wave heights have shown that wave-current interactions may explain most of the variability at scales 20 to 100 km (Ardhuin et al. 2017, Quilfen and Chapron 2019). Here we take advantage of the very low noise level of SWIM nadir beam to explore scales under 10 km, looking at the accuracy of wave height measurements in storms.

From theory, we expect that part of the short-scale variability of the estimated Hs is related to wave groups which give
random variations in wave height at scales of a few kilometers, depending on the sea state. Theory on signal envelopes links the spatial distribution of wave heights to the convolution of the wave spectrum (Rice 1944).

Here we use the fact that ocean waves spectra are routinely measured by CFOSAT’s SWIM instrument to evaluate the
theoretical contribution of wave groups to the wave height variability at scales under 10 km using the CFOSAT L2 products. For large period swells, the 500m wavelength cut-off of the L2 spectra hinders the theoretical estimate of Hs variability. In this study, this issue is overcome by looking at model spectra and comparing with L2S products. Wave groups are expected to have a bigger impact for narrow wave spectra.