Abstract's details

Wave field in tropical cyclones from SWIM observations

Eva Le Merle (CNR/ISMAR, Italy)


Daniele HAUSER (CNRS/LATMOS, France)

Event: 2022 CFOSAT Science Team Meeting

Session: Wind and waves: characterization, processes, modeling

Presentation type: Type Oral

Contribution: PDF file


The very high waves generated by the cyclones impact the maritime navigation, the risk in coastal areas and modify the ocean-atmosphere interactions. Therefore, a detailed description and a better understanding of the wave field properties under TC conditions is a topic of great relevance to oceanographic research and engineering applications.

It is known that the complex wind fields of tropical cyclone generate wave fields with complex structures. In particular, the field of significant wave height Hs was shown to be highly asymmetric with higher values in the right front quadrant, even in cases where the wind field is axi-symmetric . This was associated in the literature with the concept of "extended fetch" or “trapped waves “(Young, 2006). But later, Kudryavstev et al (2021) showed that the relative speed of the TC (defined as the displacement speed divided by maximum wind speed in the cyclone) greatly influences the asymmetric nature of field of significant wave height.

In this study, we have analyzed SWIM data over a two year period, gathering 46 SWIM passes over TC . We have classified our data set in 3 categories according to the relative speed of the TC and have then analyzed the wave properties in each of the 4 quadrants (defined in a common reference frame for all TCs) and at difference distances from the TC center. This analysis is not only on the field of significant wave height , but also on the dominant wavelength, dominant direction , and shape of the directional and omni-directional spectra.

The results will be presented in details during the conference. The main conclusions are the following. We confirm that indeed the relative displacement of the TC greatly influences the spatial behavior of the wave field. The asymmetry of the significant wave height and wavelength is the highest in TCs with moderate and slow displacement: higher and longer waves are observed in the right-front quadrant for the moderate speed cases, whereas the slow TC have the highest significant wave height and longest wavelength in the left-front quadrant. In opposite, fast moving TCs do not exhibit significant asymmetric features. For TCs of slow and moderate speed, the wave field is essentially mono-modal in direction in the front-right quadrant, with waves aligned with the TC displacement, i.e propagating at about 45° from the wind direction. In opposite, in fast moving TCs the spectra in the front right quadrant are characterized by multi-modal peaks in direction or energy broadly spread in direction. The behavior in other in other quadrants is more complex but overall, the fast moving TCs exhibit much more conditions of multi-modal wave spectra both in direction and frequency. The omni-directional spectra are found to follow the wind-wave functional shape of fetch-limited conditions, as verified by Young (2006), but we find that in fact this is true only in the quadrants where the directional spectra are mono-modal, in particular close to the center and for TCs with slow and moderate displacement speed. This finding that waves follow the functional shape of waves under fetch-limited conditions seems in contradiction with the fact that the inverse wave age (estimated by taking into account the angle between wind and waves) indicates that wave evolution is no longer under the influence of wind.

Oral presentation show times:

Room Start Date End Date
Main room Tue, Sep 13 2022,08:55 Tue, Sep 13 2022,09:20
Eva Le Merle