Examination of seasonal variation of the equatorial undercurrent termination in the Eastern Pacific diagnosed by ECCO2 -- Journal of Oceanology and Limnology,2022,40(3):870-890

	Cite this paper:
	Jie WANG, Xuezhi BAI, Hengling LENG. Examination of seasonal variation of the equatorial undercurrent termination in the Eastern Pacific diagnosed by ECCO2[J]. Journal of Oceanology and Limnology, 2022, 40(3): 870-890

Examination of seasonal variation of the equatorial undercurrent termination in the Eastern Pacific diagnosed by ECCO2

Jie WANG^1,2, Xuezhi BAI^1,2, Hengling LENG^1,2

1 College of Oceanography, Hohai University, Nanjing 210098, China;
2 Key Laboratory of Marine Hazards Forecasting, Ministry of Natural Resources, Hohai University, Nanjing 210098, China

Abstract:

Seasonal variations of the equatorial undercurrent (EUC) termination in the Eastern Pacific, and their mechanism were examined using the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2). The ECCO2 reproduced a weak and shallow eastward EUC east of the Galapagos Islands, with annual mean transport of half of EUC to the west of the Islands. The diagnosis of zonal momentum equation suggests that the zonal advection (nonlinear terms) drives the EUC beyond the Islands rather than the pressure gradient force. The EUC in the Far Eastern Pacific has the largest core velocity in boreal spring and the smallest one in boreal summer, and its volume transport exhibits two maxima in boreal spring and autumn. The seasonal variability of the EUC in the Eastern Pacific is dominated by the Kelvin and Rossby waves excited by the zonal winds anomalies in the central and Eastern Pacific that are associated with the seasonal relaxation or intensification of the trade wind. In the Far Eastern Pacific to the east of 120°W, the eastward propagation Kelvin waves play a dominate role in the seasonal cycle of the EUC, results in a semiannual fluctuation with double peaks in boreal spring and autumn. A construction of water mass budget suggests that approximately 24.1% of the EUC water east of 100°W has upwelled to the mixed layer by 0.35 m/d. The estimated upwelling is strongest during boreal autumn and weakest during boreal winter. It is also found that approximately 42.6% of the EUC turns westward to feed the south equatorial current (SEC), 13.2% flows north of the equator, and 20.1% flows south of the equator, mainly contributing to Peru-Chile undercurrent.

Key words: equatorial undercurrent termination|Eastern Pacific Ocean|Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2)|Peru-Chile undercurrent|Galapagos Islands

Received: 2020-08-10 Revised:

Tools

PDF (6841 KB) Free

Print this page

Add to favorites

Email this article to others

Authors

Articles by Jie WANG

Articles by Xuezhi BAI

Articles by Hengling LENG

References:
Blanke B, Raynaud S.1997.Kinematics of the Pacific equatorial undercurrent:an Eulerian and Lagrangian approach from GCM results.Journal of Physical Oceanography, 27(6):1038-1053, https://doi.org/10.1175/1520-0485(1997)027<1038:KOTPEU>2.0.CO;2.
Brink K H, Halpern D, Huyer A, Smith R L.1983.The physical environment of the Peruvian upwelling system.Progress in Oceanography, 12(3):285-305, https://doi.org/10.1016/0079-6611(83)90011-3.
Bryden H L, Brady E C.1985.Diagnostic model of the threedimensional circulation in the upper equatorial Pacific Ocean.Journal of Physical Oceanography, 15(10):1255-1273, https://doi.org/10.1175/1520-0485(1985)015< 1255:DMOTTD>2.0.CO;2.
Busalacchi A J, O'Brien J J.1980.The Seasonal variability in a model of the tropical Pacific.Journal of Physical Oceanography, 10(12):1929-1951, https://doi.org/10.1175/1520-0485(1980)010<1929:TSVIAM>2.0.CO;2.
Chen G X, Han W Q, Li Y L, Wang D X, McPhaden M J.2015.Seasonal-to-interannual time-scale dynamics of the equatorial undercurrent in the Indian Ocean.Journal of Physical Oceanography, 45(6):1532-1553, https://doi.org/10.1175/JPO-D-14-0225.1.
Chen G X, Han W Q, Li Y L, Yao J L, Wang D X.2019.Intraseasonal variability of the equatorial undercurrent in the Indian Ocean.Journal of Physical Oceanography, 49(1):85-101, https://doi.org/10.1175/JPO-D-18-0151.1.
Fiedler P C, Talley L D.2006.Hydrography of the eastern tropical Pacific:a review.Progress in Oceanography, 69(2-4):143-180, https://doi.org/10.1016/j.pocean.2006.03.008.
Guo H H, Chen Z H, Yang H Y.2019.Poleward shift of the Pacific north equatorial current bifurcation.Journal of Geophysical Research:Oceans, 124(7):4557-4571, https://doi.org/10.1029/2019JC015019.
Jakoboski J, Todd R E, Owens W B, Karnauskas K B, Rudnick D L.2020.Bifurcation and upwelling of the equatorial undercurrent west of the Galápagos Archipelago.Journal of Physical Oceanography, 50(4):887-905, https://doi.org/10.1175/JPO-D-19-0110.1.
Johnson G C, McPhaden M J, Firing E.2001.Equatorial Pacific Ocean horizontal velocity, divergence, and upwelling.Journal of Physical Oceanography, 31(3):839-849, https://doi.org/10.1175/1520-0485(2001)031< 0839:EPOHVD>2.0.CO;2.
Johnson G C, Sloyan B M, Kessler W S, McTaggart K E.2002.Direct measurements of upper ocean currents and water properties across the tropical Pacific during the 1990s.Progress in Oceanography, 52(1):31-61, https://doi.org/10.1016/S0079-6611(02)00021-6.
Kalnay E, Kanamitsu M, Kistler R, Collins W, Deaven D, Gandin L, Iredell M, Saha S, White G, Woollen J, Zhu Y, Chelliah M, Ebisuzaki W, Higgins W, Janowiak J, Mo K C, Ropelewski C, Wang J, Leetmaa A, Reynolds R, Jenne R, Joseph D.1996.The NCEP/NCAR 40-year reanalysis project.Bulletin of the American Meteorological Society, 77(3):437-472.
Karnauskas K B, Jenouvrier S, Brown C W, Murtugudde R.2015.Strong sea surface cooling in the eastern equatorial Pacific and implications for Galápagos Penguin conservation.Geophysical Research Letters, 42(15):6432-6437, https://doi.org/10.1002/2015GL064456.
Karnauskas K B, Murtugudde R, Busalacchi A J.2007.The effect of the Galápagos Islands on the equatorial Pacific cold tongue.Journal of Physical Oceanography, 37(5):1266-1281, https://doi.org/10.1175/JPO3048.1.
Karnauskas K B, Murtugudde R, Busalacchi A J.2008.The effect of the Galápagos Islands on ENSO in forced ocean and hybrid coupled models.Journal of Physical Oceanography, 38(11):2519-2534, https://doi.org/10.1175/2008JPO3848.1.
Karnauskas K B, Murtugudde R, Busalacchi A J.2010.Observing the Galápagos-EUC Interaction:insights and challenges.Journal of Physical Oceanography, 40(12):2768-2777, https://doi.org/10.1175/2010JPO4461.1.
Kessler W S.2006.The circulation of the eastern tropical Pacific:a review.Progress in Oceanography, 69(2-4):181-217, https://doi.org/10.1016/j.pocean.2006.03.009.
Knauss J A.1959-1960.Measurements of the Cromwell current.Deep Sea Research (1953), 6:265-286, https://doi.org/10.1016/0146-6313(59)90086-3.
Knauss J A.1966.Further measurements and observations on the Cromwell Current.Journal of Marine Research, 24(2):205-240.
Lukas R.1986.The termination of the equatorial undercurrent in the eastern Pacific.Progress in Oceanography, 16(2):63-90, https://doi.org/10.1016/0079-6611(86)90007-8.
Marshall J, Adcroft A, Hill C, Perelman L, Heisey C.1997.A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers.Journal of Geophysical Research:Oceans, 102(C3):5753-5766, https://doi.org/10.1029/96JC02775.
McPhaden M J, Busalacchi A J, Cheney R, Donguy J R, Gage K S, Halpern D, Ji M, Julian P, Meyers G, Mitchum G T, Niiler P P, Picaut J, Reynolds R W, Smith N, Takeuchi K.1998.The tropical ocean-global atmosphere observing system:a decade of progress.Journal of Geophysical Research:Oceans, 103(C7):14169-14240, https://doi.org/10.1029/97JC02906.
McPhaden M J, Taft B A.1988.Dynamics of seasonal and intraseasonal variability in the eastern equatorial Pacific.Journal of Physical Oceanography, 18(11):1713-1732, https://doi.org/10.1175/1520-0485(1988)018<1713:DOS AIV>2.0.CO;2.
Meinen C S, McPhaden M J, Johnson G C.2001.Vertical velocities and transports in the equatorial Pacific during 1993-99.Journal of Physical Oceanography, 31(11):3230-3248, https://doi.org/10.1175/1520-0485(2001)031<3230:VVATIT >2.0.CO;2.
Menemenlis D, Campin J M, Heimbach P, Hill C, Lee T, Nguyen A, Schodlok M, Zhang H.2008.ECCO2:high resolution global ocean and sea ice data synthesis.
Mercator Ocean Quarterly Newsletter, 31:13-21.
Minobe S, Takeuchi K.1995.Annual period equatorial waves in the Pacific Ocean.Journal of Geophysical Research:Oceans, 100(C9):18379-18392, https://doi.org/10.1029/95JC01666.
Montes I, Colas F, Capet X, Schneider W.2010.On the pathways of the equatorial subsurface currents in the eastern equatorial Pacific and their contributions to the Peru-Chile undercurrent.Journal of Geophysical Research:Oceans, 115(C9):C09003, https://doi.org/10.1029/2009JC005710.
Nie X W.2017.Water Sources of the Pacific Equatorial Undercurrent and Their Main Pathways.University of Chinese Academy of Sciences, Qingdao.
Qiu B, Chen S M, Powell B S, Colin P L, Rudnick D L, Schönau M C.2019.Nonlinear short-term upper ocean circulation variability in the tropical western Pacific.Oceanography, 32(4):22-31, https://doi.org/10.5670/oceanog.2019.408.
Sloyan B M, Johnson G C, Kessler W S.2003.The Pacific cold tongue:a pathway for interhemispheric exchange.Journal of Physical Oceanography, 33(5):1027-1043, https://doi.org/10.1175/1520-0485(2003)033<1027:TPCTAP>2.0.CO;2.
Steger J M, Collins C A, Chu P C.1998.Circulation in the archipiélago de colón (Galapagos Islands), November, 1993.Deep Sea Research Part II:Topical Studies in Oceanography, 45(6):1093-1114, https://doi.org/10.1016/S0967-0645(98)00015-0.
Stevenson M R, Taft B A.1971.New evidence of the equatorial undercurrent east of the Galapagos Island.Journal of Marine Research, 29(2):103-115.
Strub P T, Mesias J M, Montecino V, Rutllant J.1998.Coastal ocean circulation off western South America.Coastal segment.In:Robinson A R, Brink K H eds.The Sea.Wiley, Hoboken.p.273-314.
Toggweiler J R, Dixon K, Broecker W S.1991.The Peru upwelling and the ventilation of the South Pacific thermocline.Journal of Geophysical Research:Oceans, 96(C11):20467-20497, https://doi.org/10.1029/91JC02063.
Ubelmann C, Fu L L.2011.Vorticity structures in the tropical Pacific from a numerical simulation.Journal of Physical Oceanography, 41(8):1455-1464, https://doi.org/10.1175/2011JPO4507.1.
White W B.1969.The Equatorial Undercurrent, the South Equatorial Countercurrent, and their extensions in the south Pacific Ocean east of the Galapagos Islands during February-March, 1967.Texas A&M University, College Station.p.74.
White W B.1973.An oceanic wake in the Equatorial Undercurrent downstream from the Galapagos Archipelago.Journal of Physical Oceanography, 3(1):156-161, https://doi.org/10.1175/1520-0485(1973)003< 0156:AOWITE> 2.0.CO;2.
Wooster W S, Gilmartin M.1961.The Peru-Chile undercurrent.Journal of Marine Research, 19(3):97-122.
Wyrtki K.1963.The horizontal and vertical field of motion in the Peru current.Bulletin of the Scripps Institution of Oceanography, University of California, San Diego, 8(4):313-344.
Wyrtki K.1966.Oceanography of the eastern equatorial Pacific Ocean.Oceanography and Marine Biology:An Annual Review, 4:33-68.
Wyrtki K.1967.Circulation and water masses in the eastern equatorial Pacific Ocean.International Journal of Oceanology and Limnology, 1:117-147.
Wyrtki K.1981.An estimate of equatorial upwelling in the Pacific.Journal of Physical Oceanography, 11(9):1205-1214, https://doi.org/10.1175/1520-0485(1981)011< 1205:AEOEUI>2.0.CO;2.
Yu X R, McPhaden M J.1999a.Seasonal variability in the equatorial Pacific.Journal of Physical Oceanography, 29(5):925-947, https://doi.org/10.1175/1520-0485(1999) 029<0925:SVITEP>2.0.CO;2.
Yu X R, McPhaden M J.1999b.Dynamical analysis of seasonal and interannual variability in the equatorial Pacific.Journal of Physical Oceanography, 29(9):2350-2369, https://doi.org/10.1175/1520-0485(1999) 029<2350:DAOSAI>2.0.CO;2.
Zuta S, Rivera T, Bustamante A.1978.Hydrologic aspects of the main upwelling areas off Peru.In:Boje R, Tomczak M eds.Upwelling Ecosystems.Springer, Berlin.p.235-257.