Potential Vorticity and Instability in the Pacific Equatorial Undercurrent West of the Galápagos Archipelago
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Author(s)
Jakoboski, Julie
Todd, Robert
Owens, W
Karnauskas, Kristopher
Rudnick, Daniel
Date Issued
August 23, 2022
Journal
Journal of Physical Oceanography
Publisher
American Meteorological Society
Citation
Jakoboski, J., R. E. Todd, W. B. Owens, K. B. Karnauskas, and D. L. Rudnick, 2022: Potential Vorticity and Instability in the Pacific Equatorial Undercurrent West of the Galápagos Archipelago. J. Phys. Oceanogr., 52, 1927–1943.
Version
Final published version
Abstract
The Galápagos Archipelago lies on the equator in the path of the eastward flowing Pacific Equatorial Undercurrent (EUC). When the EUC reaches the archipelago, it upwells and bifurcates into a north and south branch around the archipelago at a latitude determined by topography. Since the Coriolis parameter (f) equals zero at the equator, strong velocity gradients associated with the EUC can result in Ertel potential vorticity (Q) having sign opposite that of planetary vorticity near the equator. Observations collected by underwater gliders deployed just west of the Galápagos Archipelago during 2013–16 are used to estimate Q and to diagnose associated instabilities that may impact the Galápagos Cold Pool. Estimates of Q are qualitatively conserved along streamlines, consistent with the 2.5-layer, inertial model of the EUC by Pedlosky. The Q with sign opposite of f is advected south of the Galápagos Archipelago when the EUC core is located south of the bifurcation latitude. The horizontal gradient of Q suggests that the region between 2°S and 2°N above 100 m is barotropically unstable, while limited regions are baroclinically unstable. Conditions conducive to symmetric instability are observed between the EUC core and the equator and within the southern branch of the undercurrent. Using 2-month and 3-yr averages, e-folding time scales are 2–11 days, suggesting that symmetric instability can persist on those time scales.
Subjects
Currents
In situ oceanic observations
Instability
Mixing
Ocean dynamics
Pacific Ocean
Potential vorticity
Tropics Jakoboski's current affiliation: MetOcean Solutions, Raglan,
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Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1175/JPO-D-21-0124.1
