Abstract's details

A study of SWIM directional wave spectra during rogue wave cases

Alice Dalphinet (Météo-France, France)


Lotfi Aouf (Météo-France, France); Eva Le Merle (ISMAR (CNR), Italy); Danièle Hauser (LATMOS (CNRS, UVSQ, Sorbonne Université), France)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: CFOSAT

Presentation type: Type Poster

The transition from wind waves to swell is accompanied by strong non-linear interactions between several wave components and also kinematic effect in presence of strong surface currents. This can lead to dangerous seas and appearance of rogue waves which need to be better forecasted for the marine safety and ship navigation. Since 2019 the SWIM instrument onboard the CFOSAT satellite mission has shown its high capacity to observe the wave directional properties for wavelength ranges from wind-wave to swell (e.g dominant wavelength between 70 and 500 m). Further directional and frequency spreading computed from SWIM wave spectra are key parameters for setting a rogue wave indicator, particularly in crossing seas conditions (Le Merle et al. 2021).
The goal of this work consists in studying cases of rogue waves and investigating whether the probability of occurrence of rogue waves is related to the specific shape of the directional wave spectra obtained with the SWIM instrument.
The wave observation of rogue or abnormal waves has been considered from the buoys of the in-situ Thematic Assembly Center network of Copernicus Marine Service (CMEMS). Only the buoy observing maximum wave height (Hmax) and with peak period greater than 8 seconds have been used. The unstable character of dangerous seas is described by the observed ratio of Hmax and Significant Wave Height (Hmax/SWH). The crossovers of buoys and CFOSAT tracks has been selected during 2020 and 2021.
Firstly, we discussed an interesting event which indicates a rogue wave case occurring during a mature and powerful storm in western Australia during the austral winter. During this event the Hmax reaches 18 meters and SWH of 8 meters is recorded. The wave spectrum from SWIM indicates a superposition of mixed sea condition with an established long wind sea that has been generated by 35 knots steady winds, and a powerful swell.
Moreover, other cases of more calm sea state but with abnormal Hmax will be briefly presented. The wave spectra associated with normal sea will also be used to define possible specific features of the spectra associated with abnormal Hmax. We have examined the relationship between the SWIM spectra and the buoys observations, particularly by using extreme indicators such as 2D Benjamin and Feir instability (BFI2D) and kurtosis.

Poster show times:

Room Start Date End Date
Mezzanine Tue, Nov 01 2022,17:15 Tue, Nov 01 2022,18:15
Mezzanine Thu, Nov 03 2022,14:00 Thu, Nov 03 2022,15:45
Alice Dalphinet