Characterization of Mixing at the Edge of a Kuroshio Intrusion into the South China Sea: Analysis of Thermal Variance Diffusivity Measurements

Alejandra Sanchez-Rios aCollege of Earth, Ocean and Atmospheric Science, Oregon State University, Corvallis, Oregon

Search for other papers by Alejandra Sanchez-Rios in
Current site
Google Scholar
PubMed
Close
https://orcid.org/0000-0003-2470-2480
,
R. Kipp Shearman aCollege of Earth, Ocean and Atmospheric Science, Oregon State University, Corvallis, Oregon

Search for other papers by R. Kipp Shearman in
Current site
Google Scholar
PubMed
Close
,
Craig M. Lee bApplied Physics Laboratory, University of Washington, Seattle, Washington

Search for other papers by Craig M. Lee in
Current site
Google Scholar
PubMed
Close
,
Harper L. Simmons bApplied Physics Laboratory, University of Washington, Seattle, Washington

Search for other papers by Harper L. Simmons in
Current site
Google Scholar
PubMed
Close
,
Louis St. Laurent bApplied Physics Laboratory, University of Washington, Seattle, Washington

Search for other papers by Louis St. Laurent in
Current site
Google Scholar
PubMed
Close
,
Andrew J. Lucas cScripps Institution of Oceanography, University of California, San Diego, San Diego, California
dDepartment of Mechanical and Aerospace Engineering, University of California, San Diego, San Diego, California

Search for other papers by Andrew J. Lucas in
Current site
Google Scholar
PubMed
Close
,
Takashi Ijichi eDepartment of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan

Search for other papers by Takashi Ijichi in
Current site
Google Scholar
PubMed
Close
, and
Sen Jan fInstitute of Oceanography, National Taiwan University, Taipei, Taiwan

Search for other papers by Sen Jan in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The Kuroshio occasionally carries warm and salty North Pacific Water into fresher waters of the South China Sea, forming a front with a complex temperature–salinity (TS) structure to the west of the Luzon Strait. In this study, we examine the TS interleavings formed by alternating layers of North Pacific Water with South China Sea Water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a free-floating wave-powered vertical profiling float to calculate the fine-scale parameters Turner angle, Tu, and Richardson number, Ri, we identified areas favorable to double-diffusion convection and shear instability observed in a TS interleaving. We evaluated the contribution of double-diffusion convection and shear instabilities to the thermal variance diffusivity, χ, using microstructure data and compared it with previous parameterization schemes based on fine-scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu > 60; Ri < ¼). In particular, χ associated with salt finger processes was an order of magnitude higher (6.7 × 10−7 K2 s−1) than in regions where only velocity shear was likely to drive mixing (8.7 × 10−8 K2 s−1).

Sanchez-Rios’s current affiliation: Scripps Institution of Oceanography, University of California, San Diego, San Diego, California.

© 2024 American Meteorological Society. This published article is licensed under the terms of the default AMS reuse license. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Alejandra Sanchez-Rios, asanchezrios@ucsd.edu

Abstract

The Kuroshio occasionally carries warm and salty North Pacific Water into fresher waters of the South China Sea, forming a front with a complex temperature–salinity (TS) structure to the west of the Luzon Strait. In this study, we examine the TS interleavings formed by alternating layers of North Pacific Water with South China Sea Water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a free-floating wave-powered vertical profiling float to calculate the fine-scale parameters Turner angle, Tu, and Richardson number, Ri, we identified areas favorable to double-diffusion convection and shear instability observed in a TS interleaving. We evaluated the contribution of double-diffusion convection and shear instabilities to the thermal variance diffusivity, χ, using microstructure data and compared it with previous parameterization schemes based on fine-scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu > 60; Ri < ¼). In particular, χ associated with salt finger processes was an order of magnitude higher (6.7 × 10−7 K2 s−1) than in regions where only velocity shear was likely to drive mixing (8.7 × 10−8 K2 s−1).

Sanchez-Rios’s current affiliation: Scripps Institution of Oceanography, University of California, San Diego, San Diego, California.

© 2024 American Meteorological Society. This published article is licensed under the terms of the default AMS reuse license. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Alejandra Sanchez-Rios, asanchezrios@ucsd.edu
Save
  • Adams, K. A., J. A. Barth, and R. K. Shearman, 2016: Intraseasonal cross-shelf variability of hypoxia along the Newport, Oregon, hydrographic line. J. Phys. Oceanogr., 46, 22192238, https://doi.org/10.1175/JPO-D-15-0119.1.

    • Search Google Scholar
    • Export Citation
  • Batchelor, G. K., 1959: Small-scale variation of convected quantities like temperature in turbulent fluid. Part 1. General discussion and the case of small conductivity. J. Fluid Mech., 5, 113133, https://doi.org/10.1017/S002211205900009X.

    • Search Google Scholar
    • Export Citation
  • Chen, C.-T. A., and M.-H. Huang, 1996: A mid-depth front separating the South China Sea water and the Philippine sea water. J. Oceanogr., 52, 1725, https://doi.org/10.1007/BF02236530.

    • Search Google Scholar
    • Export Citation
  • Fine, E. C., J. A. MacKinnon, M. H. Alford, and J. B. Mickett, 2018: Microstructure observations of turbulent heat fluxes in a warm-core Canada Basin eddy. J. Phys. Oceanogr., 48, 23972418, https://doi.org/10.1175/JPO-D-18-0028.1.

    • Search Google Scholar
    • Export Citation
  • Fine, E. C., and Coauthors, 2022: Double diffusion, shear instabilities, and heat impacts of a Pacific summer water intrusion in the Beaufort Sea. J. Phys. Oceanogr., 52, 189203, https://doi.org/10.1175/JPO-D-21-0074.1.

    • Search Google Scholar
    • Export Citation
  • Fox-Kemper, B., and Coauthors, 2019: Challenges and prospects in ocean circulation models. Front. Mar. Sci., 6, 65, https://doi.org/10.3389/fmars.2019.00065.

    • Search Google Scholar
    • Export Citation
  • Garau, B., S. Ruiz, W. G. Zhang, A. Pascual, E. Heslop, J. Kerfoot, and J. Tintoré, 2011: Thermal lag correction on Slocum CTD glider data. J. Atmos. Oceanic Technol., 28, 10651071, https://doi.org/10.1175/JTECH-D-10-05030.1.

    • Search Google Scholar
    • Export Citation
  • Holte, J., L. D. Talley, J. Gilson, and D. Roemmich, 2017: An Argo mixed layer climatology and database. Geophys. Res. Lett., 44, 56185626, https://doi.org/10.1002/2017GL073426.

    • Search Google Scholar
    • Export Citation
  • Huang, T.-H., C.-T. A. Chen, W.-Z. Zhang, and X.-F. Zhuang, 2015: Varying intensity of Kuroshio intrusion into southeast Taiwan Strait during ENSO events. Cont. Shelf Res., 103, 7987, https://doi.org/10.1016/j.csr.2015.04.021.

    • Search Google Scholar
    • Export Citation
  • Ijichi, T., L. St. Laurent, K. L. Polzin, and J. M. Toole, 2020: How variable is mixing efficiency in the abyss? Geophys. Res. Lett., 47, e2019GL086813, https://doi.org/10.1029/2019GL086813.

    • Search Google Scholar
    • Export Citation
  • IOC, SCOR, and IAPSO, 2010: The international thermodynamic equation of seawater—2010: Calculation and use of thermodynamic properties. Intergovernmental Oceanographic Commission Manuals and Guides 56, 218 pp., http://www.teos-10.org/pubs/TEOS-10_Manual.pdf.

  • Jaeger, G. S., A. J. Lucas, and A. Mahadevan, 2020: Formation of interleaving layers in the Bay of Bengal. Deep-Sea Res. II, 172, 104717, https://doi.org/10.1016/j.dsr2.2019.104717.

    • Search Google Scholar
    • Export Citation
  • Jan, S., S.-H. Wang, K.-C. Yang, Y. J. Yang, and M.-H. Chang, 2019: Glider observations of interleaving layers beneath the Kuroshio primary velocity core east of Taiwan and analyses of underlying dynamics. Sci. Rep., 9, 11401, https://doi.org/10.1038/s41598-019-47912-z.

    • Search Google Scholar
    • Export Citation
  • Kashino, Y., N. España, F. Syamsudin, K. J. Richards, T. Jensen, P. Dutrieux, and A. Ishida, 2009: Observations of the North Equatorial Current, Mindanao Current, and Kuroshio current system during the 2006/07 El Niño and 2007/08 La Niña. J. Oceanogr., 65, 325333, https://doi.org/10.1007/s10872-009-0030-z.

    • Search Google Scholar
    • Export Citation
  • Kimura, S., and W. Smyth, 2007: Direct numerical simulation of salt sheets and turbulence in a double-diffusive shear layer. Geophys. Res. Lett., 34, L21610, https://doi.org/10.1029/2007GL031935.

    • Search Google Scholar
    • Export Citation
  • Kimura, S., W. Smyth, and E. Kunze, 2011: Turbulence in a sheared, salt-fingering-favorable environment: Anisotropy and effective diffusivities. J. Phys. Oceanogr., 41, 11441159, https://doi.org/10.1175/2011JPO4543.1.

    • Search Google Scholar
    • Export Citation
  • Ko, D. S., S.-Y. Chao, C.-C. Wu, I.-I. Lin, and S. Jan, 2016: Impacts of tides and Typhoon Fanapi (2010) on seas around Taiwan. Terr. Atmos. Oceanic Sci., 27, 261280, https://doi.org/10.3319/TAO.2015.10.28.01(Oc).

    • Search Google Scholar
    • Export Citation
  • Lien, R.-C., B. Ma, Y.-H. Cheng, C.-R. Ho, B. Qiu, C. M. Lee, and M.-H. Chang, 2014: Modulation of Kuroshio transport by mesoscale eddies at the Luzon strait entrance. J. Geophys. Res. Oceans, 119, 21292142, https://doi.org/10.1002/2013JC009548.

    • Search Google Scholar
    • Export Citation
  • Mensah, V., S. Jan, M.-D. Chiou, T. H. Kuo, and R.-C. Lien, 2014: Evolution of the Kuroshio tropical water from the Luzon Strait to the east of Taiwan. Deep-Sea Res. I, 86, 6881, https://doi.org/10.1016/j.dsr.2014.01.005.

    • Search Google Scholar
    • Export Citation
  • Merrifield, S. T., L. S. Laurent, B. Owens, A. M. Thurnherr, and J. M. Toole, 2016: Enhanced diapycnal diffusivity in intrusive regions of the Drake Passage. J. Phys. Oceanogr., 46, 13091321, https://doi.org/10.1175/JPO-D-15-0068.1.

    • Search Google Scholar
    • Export Citation
  • Middleton, L., E. Fine, J. MacKinnon, M. Alford, and J. Taylor, 2021: Estimating dissipation rates associated with double diffusion. Geophys. Res. Lett., 48, e2021GL092779, https://doi.org/10.1029/2021GL092779.

    • Search Google Scholar
    • Export Citation
  • Moum, J. N., 1996: Efficiency of mixing in the main thermocline. J. Geophys. Res., 101, 12 05712 069, https://doi.org/10.1029/96JC00508.

    • Search Google Scholar
    • Export Citation
  • Moum, J. N., and J. D. Nash, 2009: Mixing measurements on an equatorial ocean mooring. J. Atmos. Oceanic Technol., 26, 317336, https://doi.org/10.1175/2008JTECHO617.1.

    • Search Google Scholar
    • Export Citation
  • Nagai, T., R. Inoue, A. Tandon, and H. Yamazaki, 2015: Evidence of enhanced double-diffusive convection below the main stream of the Kuroshio Extension. J. Geophys. Res. Oceans, 120, 84028421, https://doi.org/10.1002/2015JC011288.

    • Search Google Scholar
    • Export Citation
  • Nakano, H., and J. Yoshida, 2019: A note on estimating eddy diffusivity for oceanic double-diffusive convection. J. Oceanogr., 75, 375393, https://doi.org/10.1007/s10872-019-00514-9.

    • Search Google Scholar
    • Export Citation
  • Nan, F., H. Xue, and F. Yu, 2015: Kuroshio intrusion into the South China Sea: A review. Prog. Oceanogr., 137, 314333, https://doi.org/10.1016/j.pocean.2014.05.012.

    • Search Google Scholar
    • Export Citation
  • Nash, J. D., and J. N. Moum, 2002: Microstructure estimates of turbulent salinity flux and the dissipation spectrum of salinity. J. Phys. Oceanogr., 32, 23122333, https://doi.org/10.1175/1520-0485(2002)032<2312:MEOTSF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Nitani, H., 1972: Beginning of the Kuroshio. Kuroshio, Its Physical Aspects, K. Yoshida, Ed., University of Tokyo Press, 129–163.

  • Oakey, N. S., 1985: Statistics of mixing parameters in the upper ocean during JASIN phase 2. J. Phys. Oceanogr., 15, 16621675, https://doi.org/10.1175/1520-0485(1985)015<1662:SOMPIT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Osborn, T. R., 1980: Estimates of the local rate of vertical diffusion from dissipation measurements. J. Phys. Oceanogr., 10, 8389, https://doi.org/10.1175/1520-0485(1980)010<0083:EOTLRO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Osborn, T. R., and C. S. Cox, 1972: Oceanic fine structure. Geophys. Astrophys. Fluid Dyn., 3, 321345, https://doi.org/10.1080/03091927208236085.

    • Search Google Scholar
    • Export Citation
  • Peterson, A. K., and I. Fer, 2014: Dissipation measurements using temperature microstructure from an underwater glider. Methods Oceanogr., 10, 4469, https://doi.org/10.1016/j.mio.2014.05.002.

    • Search Google Scholar
    • Export Citation
  • Pinkel, R., M. A. Goldin, J. A. Smith, O. M. Sun, A. A. Aja, M. N. Bui, and T. Hughen, 2011: The Wirewalker: A vertically profiling instrument carrier powered by ocean waves. J. Atmos. Oceanic Technol., 28, 426435, https://doi.org/10.1175/2010JTECHO805.1.

    • Search Google Scholar
    • Export Citation
  • Qi, J., Y. Du, J. Chi, D. L. Yi, D. Li, and B. Yin, 2022: Impacts of El Niño on the South China Sea surface salinity as seen from satellites. Environ. Res. Lett., 17, 054040, https://doi.org/10.1088/1748-9326/ac6a6a.

    • Search Google Scholar
    • Export Citation
  • Qu, T., Y. Y. Kim, M. Yaremchuk, T. Tozuka, A. Ishida, and T. Yamagata, 2004: Can Luzon Strait transport play a role in conveying the impact of ENSO to the South China Sea? J. Climate, 17, 36443657, https://doi.org/10.1175/1520-0442(2004)017<3644:CLSTPA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Radko, T., 2013: Double-Diffusive Convection. Cambridge University Press, 342 pp.

  • Radko, T., and D. P. Smith, 2012: Equilibrium transport in double-diffusive convection. J. Fluid Mech., 692, 527, https://doi.org/10.1017/jfm.2011.343.

    • Search Google Scholar
    • Export Citation
  • Radko, T., A. Bulters, J. D. Flanagan, and J.-M. Campin, 2014: Double-diffusive recipes. Part I: Large-scale dynamics of thermohaline staircases. J. Phys. Oceanogr., 44, 12691284, https://doi.org/10.1175/JPO-D-13-0155.1.

    • Search Google Scholar
    • Export Citation
  • Radko, T., J. Ball, J. Colosi, and J. Flanagan, 2015: Double-diffusive convection in a stochastic shear. J. Phys. Oceanogr., 45, 31553167, https://doi.org/10.1175/JPO-D-15-0051.1.

    • Search Google Scholar
    • Export Citation
  • Ruddick, B., 1983: A practical indicator of the stability of the water column to double-diffusive activity. Deep-Sea Res., 30A, 11051107, https://doi.org/10.1016/0198-0149(83)90063-8.

    • Search Google Scholar
    • Export Citation
  • Ruddick, B., and O. Kerr, 2003: Oceanic thermohaline intrusions: Theory. Prog. Oceanogr., 56, 483497, https://doi.org/10.1016/S0079-6611(03)00029-6.

    • Search Google Scholar
    • Export Citation
  • Ruddick, B., D. Walsh, and N. Oakey, 1997: Variations in apparent mixing efficiency in the North Atlantic central water. J. Phys. Oceanogr., 27, 25892605, https://doi.org/10.1175/1520-0485(1997)027<2589:VIAMEI>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ruddick, B., A. Anis, and K. Thompson, 2000: Maximum likelihood spectral fitting: The Batchelor spectrum. J. Atmos. Oceanic Technol., 17, 15411555, https://doi.org/10.1175/1520-0426(2000)017<1541:MLSFTB>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Rudels, B., N. Kuzmina, U. Schauer, T. Stipa, and V. Zhurbas, 2009: Double-diffusive convection and interleaving in the Arctic Ocean—Distribution and importance. Geophysica, 45, 199213.

    • Search Google Scholar
    • Export Citation
  • Rudnick, D. L., and R. Ferrari, 1999: Compensation of horizontal temperature and salinity gradients in the ocean mixed layer. Science, 283, 526529, https://doi.org/10.1126/science.283.5401.526.

    • Search Google Scholar
    • Export Citation
  • Saldías, G. S., R. K. Shearman, J. A. Barth, and N. Tufillaro, 2016: Optics of the offshore Columbia River plume from glider observations and satellite imagery. J. Geophys. Res. Oceans, 121, 23672384, https://doi.org/10.1002/2015JC011431.

    • Search Google Scholar
    • Export Citation
  • Schmitt, R. W., 1994: Double diffusion in oceanography. Annu. Rev. Fluid Mech., 26, 255285, https://doi.org/10.1146/annurev.fl.26.010194.001351.

    • Search Google Scholar
    • Export Citation
  • Shaw, P.-T., 1989: The intrusion of water masses into the sea southwest of Taiwan. J. Geophys. Res., 94, 18 21318 226, https://doi.org/10.1029/JC094iC12p18213.

    • Search Google Scholar
    • Export Citation
  • Shcherbina, A. Y., M. C. Gregg, M. H. Alford, and R. R. Harcourt, 2009: Characterizing thermohaline intrusions in the North Pacific subtropical frontal zone. J. Phys. Oceanogr., 39, 27352756, https://doi.org/10.1175/2009JPO4190.1.

    • Search Google Scholar
    • Export Citation
  • Smyth, W. D., and B. Ruddick, 2010: Effects of ambient turbulence on interleaving at a baroclinic front. J. Phys. Oceanogr., 40, 685712, https://doi.org/10.1175/2009JPO4297.1.

    • Search Google Scholar
    • Export Citation
  • Smyth, W. D., and S. Kimura, 2011: Mixing in a moderately sheared salt-fingering layer. J. Phys. Oceanogr., 41, 13641384, https://doi.org/10.1175/2010JPO4611.1.

    • Search Google Scholar
    • Export Citation
  • St. Laurent, L., and R. W. Schmitt, 1999: The contribution of salt fingers to vertical mixing in the North Atlantic tracer release experiment. J. Phys. Oceanogr., 29, 14041424, https://doi.org/10.1175/1520-0485(1999)029<1404:TCOSFT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • St. Laurent, L., and S. Merrifield, 2017: Measurements of near-surface turbulence and mixing from autonomous ocean gliders. Oceanography, 30 (2), 116125, https://doi.org/10.5670/oceanog.2017.231.

    • Search Google Scholar
    • Export Citation
  • Stommel, H., and K. N. Fedorov, 1967: Small scale structure in temperature and salinity near Timor and Mindanao. Tellus, 19A, 306325, https://doi.org/10.3402/tellusa.v19i2.9792.

    • Search Google Scholar
    • Export Citation
  • Taylor, J. R., and A. F. Thompson, 2023: Submesoscale dynamics in the upper ocean. Annu. Rev. Fluid Mech., 55, 103127, https://doi.org/10.1146/annurev-fluid-031422-095147.

    • Search Google Scholar
    • Export Citation
  • Turner, J. S., 1974: Double-diffusive phenomena. Annu. Rev. Fluid Mech., 6, 3754, https://doi.org/10.1146/annurev.fl.06.010174.000345.

    • Search Google Scholar
    • Export Citation
  • Wang, J., and C.-S. Chern, 1988: On the Kuroshio branch in the Taiwan Strait during wintertime. Prog. Oceanogr., 21, 469491, https://doi.org/10.1016/0079-6611(88)90022-5.

    • Search Google Scholar
    • Export Citation
  • Yang, Q., J. Tian, W. Zhao, X. Liang, and L. Zhou, 2014a: Observations of turbulence on the shelf and slope of northern South China Sea. Deep-Sea Res. I, 87, 4352, https://doi.org/10.1016/j.dsr.2014.02.006.

    • Search Google Scholar
    • Export Citation
  • Yang, Q., L. Zhou, J. Tian, and W. Zhao, 2014b: The roles of Kuroshio intrusion and mesoscale eddy in upper mixing in the northern South China Sea. J. Coastal Res., 30, 192198, https://doi.org/10.2112/JCOASTRES-D-13-00012.1.

    • Search Google Scholar
    • Export Citation
  • Yang, Q., W. Zhao, X. Liang, and J. Tian, 2016: Three-dimensional distribution of turbulent mixing in the South China Sea. J. Phys. Oceanogr., 46, 769788, https://doi.org/10.1175/JPO-D-14-0220.1.

    • Search Google Scholar
    • Export Citation
  • You, Y., 2002: A global ocean climatological atlas of the Turner angle: Implications for double-diffusion and water-mass structure. Deep-Sea Res. I, 49, 20752093, https://doi.org/10.1016/S0967-0637(02)00099-7.

    • Search Google Scholar
    • Export Citation
  • Yu, X., A. C. Naveira Garabato, A. P. Martin, D. Gwyn Evans, and Z. Su, 2019: Wind-forced symmetric instability at a transient mid-ocean front. Geophys. Res. Lett., 46, 11 28111 291, https://doi.org/10.1029/2019GL084309.

    • Search Google Scholar
    • Export Citation
  • Zhurbas, V., and I. S. Oh, 2001: Can turbulence suppress double-diffusively driven interleaving completely? J. Phys. Oceanogr., 31, 22512254, https://doi.org/10.1175/1520-0485(2001)031<2251:CTSDDD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 663 663 88
Full Text Views 355 355 58
PDF Downloads 320 320 75