Margirier, Félix (2015) Study of convective plumes in the Gulf of Lions from high resolution in-situ data collected by gliders PFE - Project Graduation, ENSTA.

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Abstract

Numerous gliders have been deployed in the Gulf of Lions (Northwestern Mediter- ranean Sea) during episodes of open-ocean deep convection. The data collected repre- sents an unprecedented density of in-situ observations. A methodology based on a glider quasi-static flight model was applied to infer the oceanic vertical velocity signal from the glider navigation data. During the active phase of mixing, the gliders underwent significant oceanic vertical velocities (upward and downward, up to -18cm.s-1 ). The glid- ers moved along saw-tooth trajectories between the surface and a maximum depth of 1000m with a distance of 2-4km and a period of 2-4 h between surfacings. They have crossed several small scale convective plumes of mean radius of 397m and distant from each other of 1.85km on average during down and/or upcasts, giving an aspect ratio of 0.43 along glider track in the area occupied by plumes during convective events. The plumes cover 18 % of the convection area. Recording temperature and salinity as well as biogeochemical properties (dissolved oxygen, fluorescence, turbidity) along track, glid- ers detected downward velocities twice the magnitude of the upward ones (-0.061m.s-1 versus +0.025m.s-1 on average). The downward signal is of saltier (+0.001psu), colder (-0.005◦ C) and thus denser waters (0.0015kg.m-3 ). The plunging waters are also richer in oxygen (+0.2µmol.L-1 ) but no trend is detected from the fluorescence and turbidity signals despite individual correlations by plumes.

Item Type:Thesis (PFE - Project Graduation)
Uncontrolled Keywords:gliders, plumes, deep convection, Mediterranean Sea, Gulf of Lions.
Subjects:Earth Sciences and Environmental Engineering
ID Code:6596
Deposited By:Félix MARGIRIER
Deposited On:18 mai 2016 14:24
Dernière modification:18 mai 2016 14:24

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