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Potential Vorticity and Instability in the Pacific Equatorial Undercurrent West of the Galápagos Archipelago

Potential Vorticity and Instability in the Pacific Equatorial Undercurrent West of the Galápagos... AbstractThe 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.Significance StatementThe Pacific Ocean contains fast-moving currents near the equator and below the surface that result in instabilities and mixing. The Galápagos Archipelago lies directly in the path of the eastward-flowing Pacific Equatorial Undercurrent. There are few observations of what happens to the current when it reaches the Galápagos Archipelago, so theories and models of the instabilities and mixing resulting from these strong currents have not been well verified. The Repeat Observations by Gliders in the Equatorial Region (ROGER) project deployed autonomous underwater gliders to observe the current system in this region. The results show that a range of instabilities may be responsible for the cold sea surface temperature of the Galápagos Cold Pool and the generation of tropical instability waves. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Physical Oceanography American Meteorological Society

Potential Vorticity and Instability in the Pacific Equatorial Undercurrent West of the Galápagos Archipelago

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0485
eISSN
1520-0485
DOI
10.1175/jpo-d-21-0124.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThe 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.Significance StatementThe Pacific Ocean contains fast-moving currents near the equator and below the surface that result in instabilities and mixing. The Galápagos Archipelago lies directly in the path of the eastward-flowing Pacific Equatorial Undercurrent. There are few observations of what happens to the current when it reaches the Galápagos Archipelago, so theories and models of the instabilities and mixing resulting from these strong currents have not been well verified. The Repeat Observations by Gliders in the Equatorial Region (ROGER) project deployed autonomous underwater gliders to observe the current system in this region. The results show that a range of instabilities may be responsible for the cold sea surface temperature of the Galápagos Cold Pool and the generation of tropical instability waves.

Journal

Journal of Physical Oceanography – American Meteorological Society

Published: Aug 23, 2022

References

  • Richardson number criterion for the nonlinear stability of three-dimensional stratified flow
    Abarbanel, H. D. I.; Holm, D. D.; Marsden, J. E.; Ratiu, T.
  • Wind-forced submesoscale symmetric instability around deep convection in the northwestern Mediterranean Sea
    Bosse, A.; Testor, P.; Damien, P.; Estournel, C.; Marsaleix, P.; Mortier, L.; Prieur, L.; Taillandier, V.
  • World Ocean Database 2013
    Boyer, T. P.
  • Ocean turbulence. Part I: One-point closure model—Momentum and heat vertical diffusivities
    Canuto, V. M.; Howard, A.; Cheng, Y.; Dubovikov, M. S.
  • Structure of wind-driven equatorial currents in homogeneous oceans
    Charney, J. G.; Spiegel, S. L.
  • Observations of the Cromwell Current near the Galapagos Islands
    Christensen, N.
  • Turbulent kinetic energy and its dissipation rate in the equatorial mixed layer
    Clayson, C. A.; Kantha, L. H.
  • Pacific equatorial turbulence
    Crawford, W. R.
  • Equatorial undercurrent in Pacific Ocean revealed by new methods
    Cromwell, T.; Montgomery, R. B.; Stroup, E. D.
  • On the inertial stability of the equatorial middle atmosphere
    Dunkerton, T. J.
  • Ein neuer hydrodynamischer Erhaltungssatz
    Ertel, H.
  • Barotropic Rossby waves radiating from tropical instability waves in the Pacific Ocean
    Farrar, J. T.
  • The equatorial undercurrent in the light of the vorticity equation
    Fofonoff, N. P.; Montgomery, R. B.
  • Galápagos upwelling driven by localized wind–front interactions
    Forryan, A.; Naveira Garabato, A. C.; Vic, C.; Nurser, A. J. G.; Hearn, A. R.
  • Mean circulation of the upper layers of the western equatorial Pacific Ocean
    Gouriou, Y.; Toole, J.
  • Gulf Stream dynamics along the southeastern U.S. seaboard
    Gula, J.; Molemaker, M. J.; McWilliams, J. C.
  • Gravitational, symmetric, and baroclinic instability of the ocean mixed layer
    Haine, T. W. N.; Marshall, J.
  • Potential vorticity dynamics of tropical instability vortices
    Holmes, R. M.; Thomas, L. N.; Thompson, L.; Darr, D.
  • The role of potential vorticity in symmetric stability and instability
    Hoskins, B. J.
  • Bifurcation and upwelling of the equatorial undercurrent west of the Galápagos Archipelago
    Jakoboski, J.; Todd, R. E.; Owens, W. B.; Karnauskas, K. B.; Rudnick, D. L.
  • Mean zonal momentum balance in the upper and central equatorial Pacific Ocean
    Johnson, E. S.; Luther, D. S.
  • Equatorial Pacific Ocean horizontal velocity, divergence, and upwelling
    Johnson, G. C.; McPhaden, M. J.; Firing, E.
  • Direct measurements of upper ocean currents and water properties across the tropical Pacific during the 1990s
    Johnson, G. C.; Sloyan, B. M.; Kessler, W. S.; McTaggart, K. E.
  • The effect of the Galápagos Islands on the equatorial Pacific cold tongue
    Karnauskas, K. B.; Murtugudde, R.; Busalacchi, A. J.
  • Observing the Galápagos–EUC interaction: Insights and challenges
    Karnauskas, K. B.; Murtugudde, R.; Busalacchi, A. J.
  • The Pacific equatorial undercurrent in three generations of global climate models and glider observations
    Karnauskas, K. B.; Jakoboski, J.; Johnston, T. M. S.; Owens, W. B.; Rudnick, D. L.; Todd, R. E.
  • The circulation of the eastern tropical Pacific: A review
    Kessler, W. S.
  • The annual cycle of SST in the eastern tropical Pacific, diagnosed in an ocean GCM
    Kessler, W. S.; Rothstein, L. M.; Chen, D.
  • Measurements of the Cromwell current
    Knauss, J. A.
  • Observations of the Pacific equatorial undercurrent
    Knauss, J. A.; King, J. E.
  • The equatorial undercurrent and TAO sampling bias from a decade at SEA
    Leslie, W. R.; Karnauskas, K. B.
  • The termination of the equatorial undercurrent in the eastern Pacific
    Lukas, R.
  • The geostrophic balance of the Pacific equatorial undercurrent
    Lukas, R.; Firing, E.
  • Tropical instability waves as a resonance between equatorial Rossby waves
    Lyman, J. M.; Chelton, D. B.; DeSzoeke, R. A.; Samelson, R. M.
  • Distinct 17- and 33-day tropical instability waves in subsurface observations
    Lyman, J. M.; Johnson, G. C.; Kessler, W. S.
  • Submesoscale instability and generation of mesoscale anticyclones near a separation of the California Undercurrent
    Molemaker, M. J.; McWilliams, J. C.; Dewar, W. K.
  • Turbulence and internal waves at the equator. Part I: Statistics from towed thermistors and a microstructure profiler
    Moum, J. N.; Hebert, D.; Paulson, C. A.; Caldwell, D. R.
  • Seasonal patterns of sea-surface temperature and ocean color around the Galápagos: Regional and local influences
    Palacios, D. M.
  • An inertial theory of the equatorial undercurrent
    Pedlosky, J.
  • Instability theory
    Pedlosky, J.
  • Equatorial dynamics of the thermocline: The equatorial undercurrent
    Pedlosky, J.
  • Instabilities of zonal equatorial currents
    Philander, S. G. H.
  • Instabilities of zonal equatorial currents, 2
    Philander, S. G. H.
  • Finescale vertical structure of the upwelling system off southern Peru as observed from glider data
    Pietri, A.; Testor, P.; Echevin, V.; Chaigneau, A.; Mortier, L.; Eldin, G.; Grados, C.
  • The role of meridional flow asymmetry in the dynamics of tropical instability
    Proehl, J. A.
  • The zonal momentum balance of the equatorial undercurrent in the central Pacific
    Qiao, L.; Weisberg, R. H.
  • Ocean research enabled by underwater gliders
    Rudnick, D. L.
  • On sampling the ocean using underwater gliders
    Rudnick, D. L.; Cole, S. T.
  • Spray underwater glider operations
    Rudnick, D. L.; Davis, R. E.; Sherman, J. T.
  • Repeat observations by gliders in the equatorial region [data set]
    Rudnick, D. L.; Owens, W. B.; Karnauskas, K. B.; Johnston, T. M. S.
  • The equatorial current system west of the Galápagos Islands during the 2014–16 El Niño as observed by underwater gliders
    Rudnick, D. L.; Owens, W. B.; Johnston, T. M. S.; Karnauskas, K. B.; Jakoboski, J.; Todd, R. E.
  • English translations of twenty-one of Ertel’s papers on geophysical fluid dynamics
    Schubert, W.; Ruprecht, E.; Hertenstein, R.; Ferreira, R. N.; Taft, R.; Rozoff, C.; Ciesielski, P.; Kuo, H.-C.
  • The autonomous underwater glider “Spray.”
    Sherman, J.; Davis, R. E.; Owens, W. B.; Valdes, J.
  • Diurnal shear instability, the descent of the surface shear layer, and the deep cycle of equatorial turbulence
    Smyth, W. D.; Moum, J. N.; Li, L.; Thorpe, S. A.
  • On symmetric stability and instability of zonal mean flows near the equator
    Stevens, D. E.
  • Symmetric instability in the Gulf Stream
    Thomas, L. N.; Taylor, J. R.; Ferrari, R.; Joyce, T. M.
  • Open-ocean submesoscale motions: A full seasonal cycle of mixed layer instabilities from gliders
    Thompson, A. F.; Lazar, A.; Buckingham, C.; Garabato, A. C. N.; Damerell, G. M.; Heywood, K. J.
  • XLVI. Hydrokinetic solutions and observations
    Thomson, W.
  • True colors of oceanography: Guidelines for effective and accurate colormap selection
    Thyng, K.; Greene, C.; Hetland, R.; Zimmerle, H.; DiMarco, S.
  • Poleward flows in the southern California Current System: Glider observations and numerical simulation
    Todd, R. E.; Rudnick, D. L.; Mazloff, M. R.; Davis, R. E.; Cornuelle, B. D.
  • Potential vorticity structure in the North Atlantic western boundary current from underwater glider observations
    Todd, R. E.; Owens, W. B.; Rudnick, D. L.
  • Absolute velocity estimates from autonomous underwater gliders equipped with Doppler current profilers
    Todd, R. E.; Rudnick, D. L.; Sherman, J.; Owens, W. B.; George, L.
  • XLIII. On discontinuous movements of fluids
    von Helmholtz, H.
  • A bi-symmetric log transformation for wide-range data
    Webber, J. B. W.
  • Equatorial currents in the Pacific 1950 to 1970 and their relations to the trade winds
    Wyrtki, K.
  • Mean water and current structure during the Hawaii-to-Tahiti shuttle experiment
    Wyrtki, K.; Kilonsky, B.
  • Meridional asymmetry and energetics of tropical instability waves
    Yu, Z.; McCreary, J. P.; Proehl, J. A.
  • On the annual cycle of upper-ocean circulation in the eastern equatorial Pacific
    Yu, Z.; Schopf, P. S.; McCreary, J. P.
  • A new look at Richardson number mixing schemes for equatorial ocean modeling
    Zaron, E. D.; Moum, J. N.