Salvador-Vieira Guilherme

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  • Technical Report
    CALYPSO 2019 Cruise Report: field campaign in the Mediterranean
    (Woods Hole Oceanographic Institution, 2020-01) Mahadevan, Amala ; D'Asaro, Eric A. ; Allen, John T. ; Almaraz García, Pablo ; Alou-Font, Eva ; Aravind, Harilal Meenambika ; Balaguer, Pau ; Caballero, Isabel ; Calafat, Noemi ; Carbornero, Andrea ; Casas, Benjamin ; Castilla, Carlos ; Centurioni, Luca R. ; Conley, Margaret ; Cristofano, Gino ; Cutolo, Eugenio ; Dever, Mathieu ; Enrique Navarro, Angélica ; Falcieri, Francesco ; Freilich, Mara ; Goodwin, Evan ; Graham, Raymond ; Guigand, Cedric ; Hodges, Benjamin A. ; Huntley, Helga ; Johnston, T. M. Shaun ; Lankhorst, Matthias ; Lermusiaux, Pierre F. J. ; Lizaran, Irene ; Mirabito, Chris ; Miralles, A. ; Mourre, Baptiste ; Navarro, Gabriel ; Ohmart, Michael ; Ouala, Said ; Ozgokmen, Tamay M. ; Pascual, Ananda ; Pou, Joan Mateu Horrach ; Poulain, Pierre Marie ; Ren, Alice ; Tarry, Daniel R. ; Rudnick, Daniel L. ; Rubio, M. ; Ruiz, Simon ; Rypina, Irina I. ; Tintore, Joaquin ; Send, Uwe ; Shcherbina, Andrey Y. ; Torner, Marc ; Salvador-Vieira, Guilherme ; Wirth, Nikolaus ; Zarokanellos, Nikolaos
    This cruise aimed to identify transport pathways from the surface into the interior ocean during the late winter in the Alborán sea between the Strait of Gibraltar (5°40’W) and the prime meridian. Theory and previous observations indicated that these pathways likely originated at strong fronts, such as the one that separates salty Mediterranean water and the fresher water in owing from the Atlantic. Our goal was to map such pathways and quantify their transport. Since the outcropping isopycnals at the front extend to the deepest depths during the late winter, we planned the cruise at the end of the Spring, prior to the onset of thermal stratification of the surface mixed layer.
  • Article
    Seagrass deformation affects fluid instability and tracer exchange in canopy flow
    (Nature Research, 2023-03-08) Vieira, Guilherme S. ; Allshouse, Michael R. ; Mahadevan, Amala
    Monami is the synchronous waving of a submerged seagrass bed in response to unidirectional fluid flow. Here we develop a multiphase model for the dynamical instabilities and flow-driven collective motions of buoyant, deformable seagrass. We show that the impedance to flow due to the seagrass results in an unstable velocity shear layer at the canopy interface, leading to a periodic array of vortices that propagate downstream. Our simplified model, configured for unidirectional flow in a channel, provides a better understanding of the interaction between these vortices and the seagrass bed. Each passing vortex locally weakens the along-stream velocity at the canopy top, reducing the drag and allowing the deformed grass to straighten up just beneath it. This causes the grass to oscillate periodically even in the absence of water waves. Crucially, the maximal grass deflection is out of phase with the vortices. A phase diagram for the onset of instability shows its dependence on the fluid Reynolds number and an effective buoyancy parameter. Less buoyant grass is more easily deformed by the flow and forms a weaker shear layer, with smaller vortices and less material exchange across the canopy top. While higher Reynolds number leads to stronger vortices and larger waving amplitudes of the seagrass, waving amplitude is maximized at intermediate grass buoyancy. All together, our theory and computations develop an updated schematic of the instability mechanism consistent with experimental observations.