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Mini-séminaire du LHEEA 19/04/2018 : "A modulation source term for short ocean waves numerical modelling", Charles Peureux de l'IFREMER

Le Laboratoire de recherche en Hydrodynamique, Énergétique et Environnement Atmosphérique de Centrale Nantes (LHEEA) organise des mini-séminaires. Allez-y, c'est ouvert à tous !

Le 19 avril 2018 de 13:45 à 14:30

Le 19 avril 2018 de 13:45 à 14:30

Le 19 avril 2018 de 13:45 à 14:30

Le 19 avril 2018 de 13:45 à 14:30

Cette semaine à 13h45 en salle de télé-enseignement, Charles Peureux en Post-Doc à l'Ifremer vous présentera son travail sur :

"A modulation source term for short ocean waves numerical modelling"

"Short waves (1 to 10 meters wave length) are important for air-sea interactions and remote sensing, ubiquitous at the ocean surface, but are still badly represented in numerical models. For example the high frequency f-5 is not reproduced by existing parameterizations taken into account in numerical models, with strong implications on air-sea interactions, particle surface drift or sea-state dynamics. Especially, rRecent observations of their directional distributions [1,2] have evidencedrevealed that the directional bimodality can be very strong strong bimodality, i.e. short waves propagating along two directions 70° away apart from the wind direction. Although this behavior is favored by the non-linear 4-wave interactions (Longuet-Higgins 1974). Here we show that the combination of existing wind input and dissipation parameterizations with exact non-linear interactions are unable to produce the strong level of bimodality observed. numerical models such as Wavewatch III fail at quantitatively reproducing those distributions [3]. Some physical processes are still lacking however.been known as a consequence of nonlinear triad interactions [2],long has Based on the observation of short wave breaking modulated by long waves (Guimaraes 2018) using stereo-video imagery, and the numerical analysis of the modulation of short waves by long waves we find that the saturation of short waves can be modulated by a factor [1+ 2 MTF x sqrt( msslong) x cos²(θ-θlong)] where the MTF may be as large 10. The long wave mean square slope is msslong, with a dominant slope direction θlong. Based on this finding we propose a modification of the dissipation parameterization by Ardhuin et al. (2010) in which the saturation is replaced by its expected maximum value over a number of modulation cycles.

New observations are presented that support an increased short waves breaking probability when wind and swell are aligned [4], through the so-called modulation process [5]. In order to account for it, the dissipation source term of Ardhuin et al. [6] could be adapted in Wavewatch III. Preliminary result with a constant MTF show that the f-5and the strong bimodality can be reproduced when the dominant long waves are aligned with the wind. Future work will explore the variability of the MTF magnitude and look into the observations of shorter waves for further verification. Modeled short waves directional distributions are encouraging and support the intervention of modulation in establishing their bimodality."
Publié le 16 avril 2018 Mis à jour le 11 mars 2019