• Barnett, T. P., 1983: Interaction of the monsoon and Pacific trade wind system at interannual time scales. Part I: The equatorial zone. Mon. Wea. Rev., 111, 756773, https://doi.org/10.1175/1520-0493(1983)111<0756:IOTMAP>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chelton, D. B., and et al. , 2001: Observations of coupling between surface wind stress and sea surface temperature in the eastern tropical Pacific. J. Climate, 14, 14791498, https://doi.org/10.1175/1520-0442(2001)014%3C1479:OOCBSW%3E2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chu, P. C., 1995: P-vector method for determining absolute velocity from hydrographic data. Mar. Technol. Soc. J., 29, 314.

  • Cravatte, S. E., W. S. Kessler, and F. Marin, 2012: Intermediate zonal jets in the equatorial Pacific Ocean observed by Argo floats. J. Phys. Oceanogr., 42, 14751485, https://doi.org/10.1175/JPO-D-11-0206.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hayes, S. P., J. M. Toole, and L. J. Mangum, 1983: Water-mass and transport variability at 110°W in the equatorial Pacific. J. Phys. Oceanogr., 13, 153168, https://doi.org/10.1175/1520-0485(1983)013<0153:WMATVA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ishizaki, H., H. Nakano, T. Nakano, and N. Shikama, 2014: Evidence of equatorial Rossby wave propagation obtained by deep mooring observations in the western Pacific Ocean. J. Oceanogr., 70, 463488, https://doi.org/10.1007/s10872-014-0247-3.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Johnson, G. C., 2011: Deep signatures of southern tropical Indian Ocean annual Rossby waves. J. Phys. Oceanogr., 41, 19581964, https://doi.org/10.1175/JPO-D-11-029.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Johnson, G. C., B. M. Sloyan, W. S. Kessler, and K. E. McTaggart, 2002: Direct measurements of upper ocean currents and water properties across the tropical Pacific during the 1990s. Prog. Oceanogr., 52, 3161, https://doi.org/10.1016/S0079-6611(02)00021-6.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., 2002: Mean three-dimensional circulation in the northeast tropical Pacific. J. Phys. Oceanogr., 32, 24572471, https://doi.org/10.1175/1520-0485-32.9.2457.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., 2006: The circulation of the eastern tropical Pacific: A review. Prog. Oceanogr., 69, 181217, https://doi.org/10.1016/j.pocean.2006.03.009.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., and J. P. McCreary, 1993: The annual wind-driven Rossby wave in the subthermocline equatorial Pacific. J. Phys. Oceanogr., 23, 11921207, https://doi.org/10.1175/1520-0485(1993)023<1192:TAWDRW>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., and M. J. McPhaden, 1995: Oceanic equatorial waves and the 1991–93 El Nino. J. Climate, 8, 17571774, https://doi.org/10.1175/1520-0442(1995)008<1757:OEWATE>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Locarnini, R. A., and et al. , 2019: Temperature. Vol. 1, World Ocean Atlas 2018, NOAA Atlas NESDIS 81, 52 pp., https://data.nodc.noaa.gov/woa/WOA18/DOC/woa18_vol1.pdf.

  • Lukas, R., and E. Firing, 1985: The annual Rossby wave in the central equatorial Pacific Ocean. J. Phys. Oceanogr., 15, 5567, https://doi.org/10.1175/1520-0485(1985)015<0055:TARWIT>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lyman, J. M., D. B. Chelton, R. A. deSzoeke, and R. M. Samelson, 2005: Tropical instability waves as a resonance between equatorial Rossby waves. J. Phys. Oceanogr., 35, 232254, https://doi.org/10.1175/JPO-2668.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Marin, F., E. Kestenare, T. Delcroix, F. Durand, S. Cravatte, and G. Eldin, 2010: Annual reversal of the equatorial intermediate current in the Pacific: Observations and model diagnostics. J. Phys. Oceanogr., 40, 915933, https://doi.org/10.1175/2009JPO4318.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCreary, J. P., 1981: A linear stratified ocean model of the equatorial undercurrent. Philos. Trans. Roy. Soc. London, A298, 603635, https://doi.org/10.1098/rsta.1981.0002.

    • Search Google Scholar
    • Export Citation
  • Meyers, G., 1979: On the annual Rossby wave in the tropical North Pacific Ocean. J. Phys. Oceanogr., 9, 663674, https://doi.org/10.1175/1520-0485(1979)009<0663:OTARWI>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nagura, M., 2018: Annual Rossby waves below the pycnocline in the Indian Ocean. J. Geophys. Res. Oceans, 123, 94059415, https://doi.org/10.1029/2018JC014362.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Qiu, B., and R. Lukas, 1996: Seasonal and interannual variability of the north equatorial current, the Mindanao current, and the Kuroshio along the Pacific western boundary. J. Geophys. Res., 101, 12 31512 330, https://doi.org/10.1029/95JC03204.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Qiu, B., and S. Chen, 2010: Interannual variability of the North Pacific subtropical countercurrent and its associated mesoscale eddy field. J. Phys. Oceanogr., 40, 213225, https://doi.org/10.1175/2009JPO4285.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Qiu, B., S. Chen, and H. Sasaki, 2013: Generation of the north equatorial undercurrent jets by triad baroclinic Rossby wave interactions. J. Phys. Oceanogr., 43, 26822698, https://doi.org/10.1175/JPO-D-13-099.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ramos, M., B. Dewitte, O. Pizarro, and G. Garric, 2008: Vertical propagation of extratropical Rossby waves during the 1997–1998 El Niño off the west coast of South America in a medium-resolution OGCM simulation. J. Geophys. Res., 113, C08041, https://doi.org/10.1029/2007JC004681.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Roemmich, D., and J. Gilson, 2009: The 2004–2008 mean and annual cycle of temperature, salinity, and steric height in the global ocean from the Argo Program. Prog. Oceanogr., 82, 81100, https://doi.org/10.1016/j.pocean.2009.03.004.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schott, F. A., and et al. , 2003: The zonal currents and transports at 35°W in the tropical Atlantic. Geophys. Res. Lett., 30, 1349, https://doi.org/10.1029/2002GL016849.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thierry, V., H. Mercier, and A. M. Treguier, 2006: Seasonal fluctuations in the deep central equatorial Atlantic Ocean: A data–model comparison. Ocean Dyn., 56, 581593, https://doi.org/10.1007/s10236-005-0045-y.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, F., J. Wang, C. Guan, Q. Ma, and D. Zhang, 2016: Mooring observations of equatorial currents in the upper 1000 m of the western Pacific Ocean during 2014. J. Geophys. Res. Oceans, 121, 37303740, https://doi.org/10.1002/2015JC011510.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, J., and D. Yuan, 2015: Roles of western and eastern boundary reflections in the interannual sea level variations during negative Indian Ocean dipole events. J. Phys. Oceanogr., 45, 18041821, https://doi.org/10.1175/JPO-D-14-0124.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wyrtki, K., and B. Kilonsky, 1984: Mean water and current structure during the Hawaii-to-Tahiti shuttle experiment. J. Phys. Oceanogr., 14, 242254, https://doi.org/10.1175/1520-0485(1984)014<0242:MWACSD>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Yuan, D., 2005: Role of the Kelvin and Rossby waves in the seasonal cycle of the equatorial Pacific Ocean circulation. J. Geophys. Res., 110, C04004, https://doi.org/10.1029/2004JC002344.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Yuan, D., M. M. Rienecker, and P. S. Schopf, 2004: Long wave dynamics of the interannual variability in a numerical hindcast of the equatorial Pacific Ocean circulation during the 1990s. J. Geophys. Res., 109, C05019, https://doi.org/10.1029/2003JC001936.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Yuan, D., Z. Zhang, P. C. Chu, and W. K. Dewar, 2014: Geostrophic circulation in the tropical north Pacific Ocean based on Argo profiles. J. Phys. Oceanogr., 44, 558575, https://doi.org/10.1175/JPO-D-12-0230.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zhai, F., D. Hu, and T. Qu, 2013: Decadal variations of the north equatorial current in the Pacific at 137°E. J. Geophys. Res. Oceans, 118, 49895006, https://doi.org/10.1002/jgrc.20391.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zhang, Z., B. Qiu, J. Tian, W. Zhao, and X. Huang, 2018: Latitude-dependent finescale turbulent shear generations in the Pacific tropical-extratropical upper ocean. Nat. Commun., 9, 4086, https://doi.org/10.1038/S41467-018-06260-8.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zweng, M. M., and et al. , 2019: Salinity. Vol. 2, World Ocean Atlas 2018, NOAA Atlas NESDIS 82, 50 pp., https://data.nodc.noaa.gov/woa/WOA18/DOC/woa18_vol2.pdf.

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Seasonal Variability and Dynamics of the Pacific North Equatorial Subsurface Current

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  • 1 Key Laboratory of Ocean Circulation and Waves, and Institute of Oceanology, Chinese Academy of Sciences, and Function Laboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology (Qingdao), and Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, and University of Chinese Academy of Sciences, Beijing, China
  • | 2 Key Laboratory of Ocean Circulation and Waves, and Institute of Oceanology, Chinese Academy of Sciences, and Function Laboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology (Qingdao), and Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China
  • | 3 Key Laboratory of Ocean Circulation and Waves, and Institute of Oceanology, Chinese Academy of Sciences, and Function Laboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology (Qingdao), and Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, and University of Chinese Academy of Sciences, Beijing, China
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Abstract

The North Equatorial Subsurface Current (NESC) is a subthermocline ocean current uncovered recently in the tropical Pacific Ocean, flowing westward below the North Equatorial Countercurrent. In this study, the dynamics of the seasonal cycle of this current are studied using historical shipboard acoustic Doppler current profiler measurements and Argo absolute geostrophic currents. Both data show a westward current at the depths of 200–1000 m between 4° and 6°N, with a typical core speed of about 5 and 2 cm s−1, respectively. The subsurface current originates in the eastern Pacific, with its core descending to deeper isopycnal surfaces and moving to the equator as it flows westward. The zonal velocity of the NESC shows pronounced seasonal variability, with the annual-cycle harmonics of vertical isothermal displacement and zonal velocity presenting characters of vertically propagating baroclinic Rossby waves. A simple analytical Rossby wave model is employed to simulate the propagation of the seasonal variations of the westward zonal currents successfully, which is the basis for exploring the wind forcing dynamics. The results suggest that the wind curl forcing in the central-eastern basin between 170° and 140°W associated with the meridional movement of the intertropical convergence zone dominates the NESC seasonal variability in the western Pacific, with the winds west of 170°W and east of 140°W playing a minor role in the forcing.

Corresponding author: Dongliang Yuan, dyuan@qdio.ac.cn.

Abstract

The North Equatorial Subsurface Current (NESC) is a subthermocline ocean current uncovered recently in the tropical Pacific Ocean, flowing westward below the North Equatorial Countercurrent. In this study, the dynamics of the seasonal cycle of this current are studied using historical shipboard acoustic Doppler current profiler measurements and Argo absolute geostrophic currents. Both data show a westward current at the depths of 200–1000 m between 4° and 6°N, with a typical core speed of about 5 and 2 cm s−1, respectively. The subsurface current originates in the eastern Pacific, with its core descending to deeper isopycnal surfaces and moving to the equator as it flows westward. The zonal velocity of the NESC shows pronounced seasonal variability, with the annual-cycle harmonics of vertical isothermal displacement and zonal velocity presenting characters of vertically propagating baroclinic Rossby waves. A simple analytical Rossby wave model is employed to simulate the propagation of the seasonal variations of the westward zonal currents successfully, which is the basis for exploring the wind forcing dynamics. The results suggest that the wind curl forcing in the central-eastern basin between 170° and 140°W associated with the meridional movement of the intertropical convergence zone dominates the NESC seasonal variability in the western Pacific, with the winds west of 170°W and east of 140°W playing a minor role in the forcing.

Corresponding author: Dongliang Yuan, dyuan@qdio.ac.cn.
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