Generation Mechanisms of Mesoscale Eddies in the Mauritanian Upwelling Region
- 1 January 2022
- journal article
- research article
- Published by American Meteorological Society in Journal of Physical Oceanography
- Vol. 52 (1), 161-182
- https://doi.org/10.1175/jpo-d-21-0092.1
Abstract
The physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian Upwelling Region are investigated using a high-resolution (~1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveals a baroclinically unstable state during its intensification phase in boreal summer and which is driving eddy generation within the near-coastal region. The mean poleward coastal flow’s interaction with the sloping topography induces enhanced anticyclonic vorticity, with potential vorticity close to zero generated in the bottom boundary layer. Flow separation at sharp topographic bends intensifies the anticyclonic vorticity, and submesoscale structures of low PV coalesce to form anticyclonic vortices. A combination of offshore Ekman transport and horizontal advection determined the amount of SACW in an anticyclonic eddy. A vortex with a relatively dense and low PV core will form an anticyclonic mode-water eddy, which will subduct along isopycnals while propagating offshore and hence be shielded from surface buoyancy forcing. Less contribution of dense SACW promotes the generation of surface anticyclonic eddies as the core is composed of a lighter water mass, which causes the eddy to stay closer to the surface and hence be exposed to surface buoyancy forcing. Simulated cyclonic eddies are formed between the rotational flow of an offshore anticyclonic vortex and a poleward flowing boundary current, with eddy potential energy being the dominant source of eddy kinetic energy. All three types of eddies play a key role in the exchange between the Mauritanian Coastal currents system and the adjacent eastern boundary shadow zone region. The physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian Upwelling Region are investigated using a high-resolution (~1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveals a baroclinically unstable state during its intensification phase in boreal summer and which is driving eddy generation within the near-coastal region. The mean poleward coastal flow’s interaction with the sloping topography induces enhanced anticyclonic vorticity, with potential vorticity close to zero generated in the bottom boundary layer. Flow separation at sharp topographic bends intensifies the anticyclonic vorticity, and submesoscale structures of low PV coalesce to form anticyclonic vortices. A combination of offshore Ekman transport and horizontal advection determined the amount of SACW in an anticyclonic eddy. A vortex with a relatively dense and low PV core will form an anticyclonic mode-water eddy, which will subduct along isopycnals while propagating offshore and hence be shielded from surface buoyancy forcing. Less contribution of dense SACW promotes the generation of surface anticyclonic eddies as the core is composed of a lighter water mass, which causes the eddy to stay closer to the surface and hence be exposed to surface buoyancy forcing. Simulated cyclonic eddies are formed between the rotational flow of an offshore anticyclonic vortex and a poleward flowing boundary current, with eddy potential energy being the dominant source of eddy kinetic energy. All three types of eddies play a key role in the exchange between the Mauritanian Coastal currents system and the adjacent eastern boundary shadow zone region.Keywords
Funding Information
- Deutsche Forschungsgemeinschaft
- Bundesministerium für Bildung und Forschung
- Ocean Frontier Institute
- Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada
This publication has 103 references indexed in Scilit:
- Cross-shore transport variability in the California Current: Ekman upwelling vs. eddy dynamicsProgress in Oceanography, 2013
- Upwelling response to coastal wind profilesGeophysical Research Letters, 2004
- An Implicit Formula for Boundary Current SeparationJournal of Physical Oceanography, 2001
- Lagrangian Exploration of the California Undercurrent, 1992–95Journal of Physical Oceanography, 1999
- The Vertical Partition of Oceanic Horizontal Kinetic EnergyJournal of Physical Oceanography, 1997
- Wind-driven Coastal Generation of Annual Mesoscale Eddy Activity in the California CurrentJournal of Physical Oceanography, 1993
- Evolution of a Mediterranean Salt Lens: Scalar PropertiesJournal of Physical Oceanography, 1990
- On the dynamics of the California Current systemJournal of Marine Research, 1987
- Submesoscale, coherent vortices in the oceanReviews of Geophysics, 1985
- The role of potential vorticity in symmetric stability and instabilityQuarterly Journal of the Royal Meteorological Society, 1974