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Although El Niño‐Southern Oscillation (ENSO) and its global impacts through teleconnection have been known for decades, if and how the mean currents and mesoscale eddies in the Caribbean Sea are linked to ENSO remains an open question. Here, by analyzing satellite observations and an ocean reanalysis product, we found a close connection between mean currents, eddies in the Caribbean Sea and ENSO on interannual timescales. Strong El Niño events result in enhanced north‐south sea surface height differences and consequently stronger mean currents in the Caribbean Sea, and the opposite happens during La Niña events. The eddy kinetic energy responds to ENSO via eddy‐mean flow interaction, primarily through baroclinic instability, which releases the available potential energy stored in the mean currents to mesoscale eddies. Our results suggest some predictability of the mean currents and eddies in the Caribbean Sea, particularly during strong El Niño and La Niña events.
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The influence of Caribbean Current eddies on coastal circulation in the Southwest Caribbean Sea
Abstract Westward-propagating Caribbean Current eddies modify the volume-integrated potential vorticity (PV) balance in the western Caribbean Sea, influencing the circulation of the Panamá-Colombia Gyre (PCG) and of coastal currents hundreds of kilometers to the south of the eddies’ mean trajectory. Using 22 years of output from the Hybrid Coordinate Ocean Model, we apply a volume-integrated eddy phase-averaged 1.5 layer PV balance, showing that PV fluxes into the PCG region are balanced by frictional PV dissipation represented by linear drag along the coastline. Coastal currents in the PCG region vary by a factor of two in phase with the passage of a Caribbean Current eddy over the 116 day average eddy period. Flow separation at the Isthmus of Panamá results in a vortex shed from Darien Gulf, which slows the coastal currents in the gyre region from their maximum during eddy events. An annual ensemble average PV balance in the gyre region shows that the mean PV influx to this region is higher from August to October. Correspondingly, the range of coastal currents in the gyre region over an eddy event is modestly influenced by the PV influx magnitude. Eddy influenced reversals in the coastal current can occur between November and July at Bocas del Toro and year-round at Colón. Such coastal current reversals are important for alonghshore transport of larvae, freshwater, and chemical tracers.
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- Award ID(s):
- 1924551
- PAR ID:
- 10530860
- Publisher / Repository:
- Journal of Physical Oceanography
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- ISSN:
- 0022-3670
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Beaufort Gyre (BG) is hypothesized to be partially equilibrated by those mesoscale eddies that form via baroclinic instabilities of its currents. However, our understanding of the eddy field’s dependence on the mean BG currents and the role of sea ice remains incomplete. This theoretical study explores the scales and vertical structures of eddies forming specifically due to baroclinic instabilities of interior BG flows. An idealized quasi-geostrophic model is used to show that flows driven only by the Ekman pumping contain no interior potential vorticity (PV) gradients and generate weak and large eddies, ℴ(200km) in size, with predominantly barotropic and first baroclinic mode energy. However, flows containing realistic interior PV gradients in the Pacific halocline layer generate significantly smaller eddies of about 50 km in size, with a distinct second baroclinic mode structure and a subsurface kinetic energy maximum. The dramatic change in eddy characteristics is shown to be caused by the stirring of interior PV gradients by large-scale barotropic eddies. The sea ice-ocean drag is identified as the dominant eddy dissipation mechanism, leading to realistic sub-surface maxima of eddy kinetic energy for drag coefficients higher than about 2×10 −3 . A scaling law is developed for the eddy potential enstrophy, demonstrating that it is directly proportional to the interior PV gradient and the square root of the barotropic eddy kinetic energy. This study proposes a possible formation mechanism of large BG eddies and points to the importance of accurate representation of the interior PV gradients and eddy dissipation by ice-ocean drag in BG simulations and theory.more » « less
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Abstract Numerous eddies in the coastal ocean may experience distortion due to interactions with the ambient flow. Here we investigate how coastal submesoscale eddy distortion affects the cross‐shore and vertical tracer transport using a high‐resolution, wave‐current coupled model in the La Jolla Canyon region within the Southern California Bight. Model dye is released representing freshwater discharges. Model validations show that the coupled model has weaker stratification and weaker currents. Analyses primarily focus on an eddy‐induced cross‐shore dye transport event. The results show that, the coastal eddy is squeezed in the alongshore direction and extends in the cross‐shore direction, driving cross‐shore dye transport. Along a mid‐shelf boundary, the total cross‐shore transport is found to be dominated by the along‐boundary perturbation flow, which is linked to the eddy distortion. In addition, this coastal eddy also possesses vigorous vertical motions. The vertical velocity is more negative on the eddy northern side, favoring local dye subduction. This N‐S vertical velocity asymmetry may largely be induced by the topographic beta effect and the weaker modeled stratification may strengthen this effect. Overall, coastal eddy distortion contributes to the offshore tracer transport and induces spatially non‐uniform vertical dye flux.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1175/JPO-D-24-0049.1
