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Jeudi 24 janvier - Linear wind-forced beta-plumes with application to the Hawaiian Lee Countercurrent

Par SEMSOU Dernière modification 17/05/2013 11:29
Quand ? Le 24/01/2013,
de 11:00 à 12:30
Où ? Salle Coriolis
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Participants Dr. Ali Belmadani, University of Hawai'i at Manoa
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Dr. Ali Belmadani, University of Hawai'i at Manoa

 

Linear wind-forced beta-plumes with application to the Hawaiian Lee Countercurrent


Abstract : Two numerical ocean models are used to study the baroclinic response to forcing by localized wind-stress curl (i.e., a wind-forced β-plume, which is a circulation cell developing to the west from the source region and comprised of a set of zonal jets): an idealized primitive-equation model (ROMS), and a global, eddy-resolving, general circulation model (OFES). In addition, theoretical ideas inferred from a linear continuously-stratified model are used to interpret results. In ROMS, vertical mixing preferentially damps higher-order vertical modes. The damping thickens the plume west of the forcing region, weakening the near-surface zonal jets and generating deeper zonal currents. The zonal damping scale varies monotonically with the meridional forcing scale, indicating a dominant role of vertical viscosity over diffusion, a consequence of the small forcing scale. In OFES, the Hawaiian Lee Countercurrent (HLCC) has a vertical structure consistent with that of idealized β-plumes once the contribution of the North Equatorial Current (NEC) has been removed: without this procedure, a deep HLCC branch appears artificially separated from the surface branch by the large-scale intermediate-depth NEC. The HLCC in OFES also exhibits a sensitivity to the meridional wind curl scale that agrees with the dynamics of a β-plume in the presence of vertical viscosity. The existence of the deep HLCC extension is confirmed by velocities of Argo floats.

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