Understanding the impact of Langmuir cells on Sargassum rafts dynamics using LES modeling

See the subject on the ADUM website

Start date : October 1, 2021

Deadline : June 9, 2021

Supervisor : Julien Jouanno

Co-supervision of thesis : Patrick Marchesiello

Funding: Competition for a doctoral contract

Summary

The aim of this PhD project is specifically to make progress on our understanding of the consequences of wave-current-wind interactions on the distribution of Sargassum and on their drift properties. The project mainly relies on Large Eddy Simulation (LES) and will be conducted in three stages:

1. The set-up of an idealized high-resolution simulation (x~3m) of a portion of tropical ocean, based on the non-hydrostatic hydrodynamic model CROCO (Coastal and Regional Ocean COmmunity Model), extended to account for Sargassum transport and its interactions with surrounding water and winds. Model assessment will be achieved through comparison with state of the art LES modeling of Langmuir cells and ocean color observations which will provide information on the surface organization of the Sargassum rafts (Sentinel 2 for high resolution monitoring, x~10m; and geostationary GOES for high frequency monitoring t~15mn).

2. The model will be used to perform a systematic and comprehensive analysis of Sargassum distribution, drift and sinking properties as a function of the sea state (waves and swell, wind, mixed-layer depth). Aggregation and relaxation times scales will be quantified.

3. According to student progress, the model domain will be extended to reproduce sub-mesoscale turbulence in order to investigate possible synergies between Langmuir cells and submesoscale upper ocean dynamics in aggregating the Sargassum.

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