Generation Mechanisms of SST Anomalies Associated with the Canonical El Niño Focusing on Vertical Mixing

Kouya Nakamura aDepartment of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan

Search for other papers by Kouya Nakamura in
Current site
Google Scholar
PubMed
Close
,
Shoichiro Kido bApplication Laboratory, Research Institute for Value‐Added‐Information Generation, Japan Agency for Marine‐Earth Science and Technology (JAMSTEC), Yokohama, Japan

Search for other papers by Shoichiro Kido in
Current site
Google Scholar
PubMed
Close
,
Takashi Ijichi aDepartment of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan

Search for other papers by Takashi Ijichi in
Current site
Google Scholar
PubMed
Close
, and
Tomoki Tozuka aDepartment of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan
bApplication Laboratory, Research Institute for Value‐Added‐Information Generation, Japan Agency for Marine‐Earth Science and Technology (JAMSTEC), Yokohama, Japan

Search for other papers by Tomoki Tozuka in
Current site
Google Scholar
PubMed
Close
https://orcid.org/0000-0001-6738-1299
Restricted access

Abstract

The mean vertical advection of anomalous vertical temperature gradient is considered the dominant generation mechanism of positive sea surface temperature (SST) anomalies associated with the canonical El Niño. However, most past studies had a residual term in their heat budget analysis and/or did not quantify the role of vertical mixing even though active vertical turbulent mixing in the upper ocean is observed in the eastern equatorial Pacific. To quantitatively assess the importance of vertical mixing, a mixed layer heat budget analysis is performed using a hindcast simulation forced by daily mean atmospheric reanalysis data. It is found that when the mixed layer depth is defined as the depth at which potential density increases by 0.125 kg m−3 from the sea surface, the development of positive SST anomalies is predominantly governed by reductions in the cooling by vertical mixing, and their magnitude is much larger than those by vertical advection. The anomalous warming by vertical mixing may be partly explained by an anomalous deepening of the thermocline that leads to a decrease in the vertical temperature gradient, giving rise to suppression of the climatological cooling by vertical mixing. Also, an anomalously thick mixed layer reduces sensitivity to cooling by the mean vertical mixing and contributes to the anomalous SST warming. On the other hand, the dominant negative feedbacks are attributed to both anomalous surface heat loss and anomalous deepening of the mixed layer that weakens warming by the mean surface heat flux.

© 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: Tomoki Tozuka, tozuka@eps.s.u-tokyo.ac.jp

Abstract

The mean vertical advection of anomalous vertical temperature gradient is considered the dominant generation mechanism of positive sea surface temperature (SST) anomalies associated with the canonical El Niño. However, most past studies had a residual term in their heat budget analysis and/or did not quantify the role of vertical mixing even though active vertical turbulent mixing in the upper ocean is observed in the eastern equatorial Pacific. To quantitatively assess the importance of vertical mixing, a mixed layer heat budget analysis is performed using a hindcast simulation forced by daily mean atmospheric reanalysis data. It is found that when the mixed layer depth is defined as the depth at which potential density increases by 0.125 kg m−3 from the sea surface, the development of positive SST anomalies is predominantly governed by reductions in the cooling by vertical mixing, and their magnitude is much larger than those by vertical advection. The anomalous warming by vertical mixing may be partly explained by an anomalous deepening of the thermocline that leads to a decrease in the vertical temperature gradient, giving rise to suppression of the climatological cooling by vertical mixing. Also, an anomalously thick mixed layer reduces sensitivity to cooling by the mean vertical mixing and contributes to the anomalous SST warming. On the other hand, the dominant negative feedbacks are attributed to both anomalous surface heat loss and anomalous deepening of the mixed layer that weakens warming by the mean surface heat flux.

© 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: Tomoki Tozuka, tozuka@eps.s.u-tokyo.ac.jp

Supplementary Materials

    • Supplemental Materials (PDF 0.9402 MB)
Save
  • An, S.-I., E. Tziperman, Y. M. Okumura, and T. Li, 2020: ENSO irregularity and asymmetry. El Niño Southern Oscillation in a Changing Climate, A. Santoso et al., Eds., Geophysical Monograph Series, Vol. 253, Amer. Geophys. Union, 153–172, https://doi.org/10.1002/9781119548164.ch7.

  • Ashok, K., S. K. Behera, S. A. Rao, H. Weng, and T. Yamagata, 2007: El Niño Modoki and its possible teleconnection. J. Geophys. Res., 112, C11007, https://doi.org/10.1029/2006JC003798.

    • Search Google Scholar
    • Export Citation
  • Balmaseda, M. A., K. Mogensen, and A. T. Weaver, 2013: Evaluation of the ECMWF ocean reanalysis system ORAS4. Quart. J. Roy. Meteor. Soc., 139, 11321161, https://doi.org/10.1002/qj.2063.

    • Search Google Scholar
    • Export Citation
  • Bayr, T., and M. Latif, 2023: ENSO atmospheric feedbacks under global warming and their relation to mean-state changes. Climate Dyn., 60, 26132631, https://doi.org/10.1007/s00382-022-06454-3.

    • Search Google Scholar
    • Export Citation
  • Bayr, T., D. Dommenget, and M. Latif, 2020: Walker circulation controls ENSO atmospheric feedbacks in uncoupled and coupled climate model simulations. Climate Dyn., 54, 28312846, https://doi.org/10.1007/s00382-020-05152-2.

    • Search Google Scholar
    • Export Citation
  • Bjerknes, J., 1969: Atmospheric teleconnections from the equatorial Pacific. Mon. Wea. Rev., 97, 163172, https://doi.org/10.1175/1520-0493(1969)097<0163:ATFTEP>2.3.CO;2.

    • Search Google Scholar
    • Export Citation
  • Boucharel, J., A. Timmermann, A. Santoso, M. H. England, F.-F. Jin, and M. A. Balmaseda, 2015: A surface layer variance heat budget for ENSO. Geophys. Res. Lett., 42, 35293537, https://doi.org/10.1002/2015GL063843.

    • Search Google Scholar
    • Export Citation
  • Brown, J. N., and A. V. Fedorov, 2010: Estimating the diapycnal transport contribution to warm water volume variations in the tropical Pacific Ocean. J. Climate, 23, 221237, https://doi.org/10.1175/2009JCLI2347.1.

    • Search Google Scholar
    • Export Citation
  • Burgers, G., and D. B. Stephenson, 1999: The “normality” of El Niño. Geophys. Res. Lett., 26, 10271030, https://doi.org/10.1029/1999GL900161.

    • Search Google Scholar
    • Export Citation
  • Capotondi, A., 2013: ENSO diversity in the NCAR CCSM4 climate model. J. Geophys. Res. Oceans, 118, 47554770, https://doi.org/10.1002/jgrc.20335.

    • Search Google Scholar
    • Export Citation
  • Cherian, D. A., D. B. Whitt, R. M. Holmes, R.-C. Lien, S. D. Bachman, and W. G. Large, 2021: Off-equatorial deep-cycle turbulence forced by tropical instability waves in the equatorial Pacific. J. Phys. Oceanogr., 51, 15751593, https://doi.org/10.1175/JPO-D-20-0229.1.

    • Search Google Scholar
    • Export Citation
  • Deppenmeier, A.-L., F. O. Bryan, W. S. Kessler, and L. Thompson, 2021: Modulation of cross-isothermal velocities with ENSO in the tropical Pacific cold tongue. J. Phys. Oceanogr., 51, 15591574, https://doi.org/10.1175/JPO-D-20-0217.1.

    • Search Google Scholar
    • Export Citation
  • Deppenmeier, A.-L., F. O. Bryan, W. S. Kessler, and L. Thompson, 2022: Diabatic upwelling in the tropical Pacific: Seasonal and subseasonal variability. J. Phys. Oceanogr., 52, 26572668, https://doi.org/10.1175/JPO-D-21-0316.1.

    • Search Google Scholar
    • Export Citation
  • Fairall, C. W., E. F. Bradley, J. E. Hare, A. A. Grachev, and J. B. Edson, 2003: Bulk parameterization of air–sea fluxes: Updates and verification for the COARE algorithm. J. Climate, 16, 571591, https://doi.org/10.1175/1520-0442(2003)016<0571:BPOASF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Furuichi, N., and T. Hibiya, 2015: Assessment of the upper-ocean mixed layer parameterizations using a large eddy simulation model. J. Geophys. Res. Oceans, 120, 23502369, https://doi.org/10.1002/2014JC010665.

    • Search Google Scholar
    • Export Citation
  • Furuichi, N., T. Hibiya, and Y. Niwa, 2012: Assessment of turbulence closure models for resonant inertial response in the oceanic mixed layer using a large eddy simulation model. J. Oceanogr., 68, 285294, https://doi.org/10.1007/s10872-011-0095-3.

    • Search Google Scholar
    • Export Citation
  • Graham, F. S., J. N. Brown, C. Langlais, S. J. Marsland, A. T. Wittenberg, and N. J. Holbrook, 2014: Effectiveness of the Bjerknes stability index in representing ocean dynamics. Climate Dyn., 43, 23992414, https://doi.org/10.1007/s00382-014-2062-3.

    • Search Google Scholar
    • Export Citation
  • Gregg, M. C., H. Peters, J. C. Wesson, N. S. Oakey, and T. J. Shay, 1985: Intensive measurements of turbulence and shear in the equatorial undercurrent. Nature, 318, 140144, https://doi.org/10.1038/318140a0.

    • Search Google Scholar
    • Export Citation
  • Guilyardi, E., A. Wittenberg, A. Fedorov, M. Collins, C. Wang, A. Capotondi, G. J. van Oldenborgh, and T. Stockdale, 2009: Understanding El Niño in ocean–atmosphere general circulation models: Progress and challenges. Bull. Amer. Meteor. Soc., 90, 325340, https://doi.org/10.1175/2008BAMS2387.1.

    • Search Google Scholar
    • Export Citation
  • Han, W., and Coauthors, 2022: Sea level extremes and compounding marine heatwaves in coastal Indonesia. Nat. Commun., 13, 6410, https://doi.org/10.1038/s41467-022-34003-3.

    • Search Google Scholar
    • Export Citation
  • Holmes, R. M., J. D. Zika, and M. H. England, 2019: Diathermal heat transport in a global ocean model. J. Phys. Oceanogr., 49, 141161, https://doi.org/10.1175/JPO-D-18-0098.1.

    • Search Google Scholar
    • Export Citation
  • Horel, J. D., 1982: On the annual cycle of the tropical Pacific atmosphere and ocean. Mon. Wea. Rev., 110, 18631878, https://doi.org/10.1175/1520-0493(1982)110<1863:OTACOT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Huang, B., Y. Xue, D. Zhang, A. Kumar, and M. J. McPhaden, 2010: The NCEP GODAS ocean analysis of the tropical Pacific mixed layer heat budget on seasonal to interannual time scales. J. Climate, 23, 49014925, https://doi.org/10.1175/2010JCLI3373.1.

    • Search Google Scholar
    • Export Citation
  • Huang, B., Y. Xue, H. Wang, W. Wang, and A. Kumar, 2012: Mixed layer heat budget of the El Niño in NCEP climate forecast system. Climate Dyn., 39, 365381, https://doi.org/10.1007/s00382-011-1111-4.

    • Search Google Scholar
    • Export Citation
  • Huguenin, M. F., R. M. Holmes, and M. H. England, 2020: Key role of diabatic processes in regulating warm water volume variability over ENSO events. J. Climate, 33, 99459964, https://doi.org/10.1175/JCLI-D-20-0198.1.

    • Search Google Scholar
    • Export Citation
  • Jin, F.-F., 1997: An equatorial ocean recharge paradigm for ENSO. Part I: Conceptual model. J. Atmos. Sci., 54, 811829, https://doi.org/10.1175/1520-0469(1997)054<0811:AEORPF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Jin, F.-F., and S.-I. An, 1999: Thermocline and zonal advective feedbacks within the equatorial ocean recharge oscillator model for ENSO. Geophys. Res. Lett., 26, 29892992, https://doi.org/10.1029/1999GL002297.

    • 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.

    • Search Google Scholar
    • Export Citation
  • Kao, H.-Y., and J.-Y. Yu, 2009: Contrasting eastern-Pacific and central-Pacific types of ENSO. J. Climate, 22, 615632, https://doi.org/10.1175/2008JCLI2309.1.

    • Search Google Scholar
    • Export Citation
  • Kataoka, T., T. Tozuka, and T. Yamagata, 2017: Generation and decay mechanisms of Ningaloo Niño/Niña. J. Geophys. Res. Oceans, 122, 89138932, https://doi.org/10.1002/2017JC012966.

    • Search Google Scholar
    • Export Citation
  • Kido, S., T. Tozuka, and W. Han, 2019a: Anatomy of salinity anomalies associated with the positive Indian Ocean Dipole. J. Geophys. Res. Oceans, 124, 81168139, https://doi.org/10.1029/2019JC015163.

    • Search Google Scholar
    • Export Citation
  • Kido, S., T. Tozuka, and W. Han, 2019b: Experimental assessments on impacts of salinity anomalies on the positive Indian Ocean Dipole. J. Geophys. Res. Oceans, 124, 94629486, https://doi.org/10.1029/2019JC015479.

    • Search Google Scholar
    • Export Citation
  • Kim, S.-B., I. Fukuomori, and T. Lee, 2006: The closure of the ocean mixed layer temperature budget using level-coordinate model fields. J. Atmos. Oceanic Technol., 23, 840853, https://doi.org/10.1175/JTECH1883.1.

    • Search Google Scholar
    • Export Citation
  • Kug, J.-S., J. Choi, S.-I. An, F.-F. Jin, and A. T. Wittenberg, 2010: Warm pool and cold tongue El Niño events as simulated by the GFDL 2.1 coupled GCM. J. Climate, 23, 12261239, https://doi.org/10.1175/2009JCLI3293.1.

    • Search Google Scholar
    • Export Citation
  • Kusunoki, H., S. Kido, and T. Tozuka, 2021: Air-sea interaction in the western tropical Pacific and its impact on asymmetry of the Ningaloo Niño/Niña. Geophys. Res. Lett., 48, e2021GL093370, https://doi.org/10.1029/2021GL093370.

    • Search Google Scholar
    • Export Citation
  • Lengaigne, M., U. Hausmann, G. Madec, C. Menkes, J. Vialard, and J. M. Molines, 2012: Mechanisms controlling warm water volume interannual variations in the equatorial Pacific: Diabatic versus adiabatic processes. Climate Dyn., 38, 10311046, https://doi.org/10.1007/s00382-011-1051-z.

    • Search Google Scholar
    • Export Citation
  • Meinen, C. S., and M. J. McPhaden, 2000: Observations of warm water volume changes in the equatorial Pacific and their relationship to El Niño and La Niña. J. Climate, 13, 35513559, https://doi.org/10.1175/1520-0442(2000)013<3551:OOWWVC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Moisan, J. R., and P. P. Niiler, 1998: The seasonal heat budget of the North Pacific: Net heat flux and heat storage rates (1950–1990). J. Phys. Oceanogr., 28, 401421, https://doi.org/10.1175/1520-0485(1998)028<0401:TSHBOT>2.0.CO;2.

    • 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
  • Moum, J. N., A. Perlin, J. D. Nash, and M. J. McPhaden, 2013: Seasonal sea surface cooling in the equatorial Pacific cold tongue controlled by ocean mixing. Nature, 500, 6467, https://doi.org/10.1038/nature12363.

    • Search Google Scholar
    • Export Citation
  • Moum, J. N., and Coauthors, 2022: Deep cycle turbulence in Atlantic and Pacific cold tongues. Geophys. Res. Lett., 49, e2021GL097345, https://doi.org/10.1029/2021GL097345.

    • Search Google Scholar
    • Export Citation
  • Moum, J. N., W. D. Smyth, K. G. Hughes, D. Cherian, S. J. Warner, B. Bourlès, P. Brandt, and M. Dengler, 2023: Wind dependencies of deep cycle turbulence in the equatorial cold tongues. J. Phys. Oceanogr., 53, 19791995, https://doi.org/10.1175/JPO-D-22-0203.1.

    • Search Google Scholar
    • Export Citation
  • Nakazato, M., S. Kido, and T. Tozuka, 2021: Mechanisms of asymmetry in sea surface temperature anomalies associated with the Indian Ocean Dipole revealed by closed heat budget. Sci. Rep., 11, 22546, https://doi.org/10.1038/s41598-021-01619-2.

    • Search Google Scholar
    • Export Citation
  • Pacanowski, R. C., 1987: Effect of equatorial currents on surface stress. J. Phys. Oceanogr., 17, 833838, https://doi.org/10.1175/1520-0485(1987)017<0833:EOECOS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Racault, M.-F., S. Sathyendranath, R. J. W. Brewin, D. E. Raitsos, T. Jackson, and T. Platt, 2017: Impact of El Niño variability on oceanic phytoplankton. Front. Mar. Sci., 4, 133, https://doi.org/10.3389/fmars.2017.00133.

    • Search Google Scholar
    • Export Citation
  • Ray, S., A. T. Wittenberg, S. M. Griffies, and F. Zeng, 2018: Understanding the equatorial Pacific cold tongue time-mean heat budget. Part I: Diagnostic framework. J. Climate, 31, 99659985, https://doi.org/10.1175/JCLI-D-18-0152.1.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., D. E. Parker, E. B. Horton, C. K. Folland, L. V. Alexander, D. P. Rowell, E. C. Kent, and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108, 4407, https://doi.org/10.1029/2002JD002670.

    • Search Google Scholar
    • Export Citation
  • Shchepetkin, A. F., and J. C. McWilliams, 2005: The Regional Oceanic Modeling System (ROMS): A split-explicit, free-surface, topography-following-coordinate oceanic model. Ocean Modell., 9, 347404, https://doi.org/10.1016/j.ocemod.2004.08.002.

    • Search Google Scholar
    • Export Citation
  • Stockdale, T. N., A. J. Busalacchi, D. E. Harrison, and R. Seager, 1998: Ocean modeling for ENSO. J. Geophys. Res., 103, 14 32514 355, https://doi.org/10.1029/97JC02440.

    • Search Google Scholar
    • Export Citation
  • Suzuki, T., D. Yamazaki, H. Tsujino, Y. Komuro, H. Nakano, and S. Urakawa, 2018: A dataset of continental river discharge based on JRA-55 for use in a global ocean circulation model. J. Oceanogr., 74, 421429, https://doi.org/10.1007/s10872-017-0458-5.

    • Search Google Scholar
    • Export Citation
  • Tatebe, H., and H. Hasumi, 2010: Formation mechanism of the Pacific equatorial thermocline revealed by a general circulation model with a high accuracy tracer advection scheme. Ocean Modell., 35, 245252, https://doi.org/10.1016/j.ocemod.2010.07.011.

    • Search Google Scholar
    • Export Citation
  • Timmermann, A., and Coauthors, 2018: El Niño–Southern Oscillation complexity. Nature, 559, 535545, https://doi.org/10.1038/s41586-018-0252-6.

    • Search Google Scholar
    • Export Citation
  • Tozuka, T., and T. Yamagata, 2003: Annual ENSO. J. Phys. Oceanogr., 33, 15641578, https://doi.org/10.1175/2414.1.

  • Tozuka, T., S. Ohishi, and M. F. Cronin, 2018: A metric for surface heat flux effect on horizontal sea surface temperature gradients. Climate Dyn., 51, 547561, https://doi.org/10.1007/s00382-017-3940-2.

    • Search Google Scholar
    • Export Citation
  • Tozuka, T., T. Toyoda, and M. F. Cronin, 2023: Role of mixed layer depth in Kuroshio Extension decadal variability. Geophys. Res. Lett., 50, e2022GL101846, https://doi.org/10.1029/2022GL101846.

    • Search Google Scholar
    • Export Citation
  • Tsujino, H., and Coauthors, 2018: JRA-55 based surface dataset for driving ocean–sea-ice models (JRA55-do). Ocean Modell., 130, 79139, https://doi.org/10.1016/j.ocemod.2018.07.002.

    • Search Google Scholar
    • Export Citation
  • Walin, G., 1982: On the relation between sea-surface heat flow and thermal circulation in the ocean. Tellus, 34A, 187195, https://doi.org/10.3402/tellusa.v34i2.10801.

    • Search Google Scholar
    • Export Citation
  • Wang, C., 2018: A review of ENSO theories. Natl. Sci. Rev., 5, 813825, https://doi.org/10.1093/nsr/nwy104.

  • Wang, W., and M. J. McPhaden, 2001: Surface layer temperature balance in the equatorial Pacific during the 1997–98 El Niño and 1998–99 La Niña. J. Climate, 14, 33933407, https://doi.org/10.1175/1520-0442(2001)014<3393:SLTBIT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Warner, S. J., and J. N. Moum, 2019: Feedback of mixing to ENSO phase change. Geophys. Res. Lett., 46, 13 92013 927, https://doi.org/10.1029/2019GL085415.

    • Search Google Scholar
    • Export Citation
  • Wyrtki, K., 1985: Water displacements in the Pacific and the genesis of El Niño cycles. J. Geophys. Res., 90, 71297132, https://doi.org/10.1029/JC090iC04p07129.

    • Search Google Scholar
    • Export Citation
  • Yeh, S.-W., and Coauthors, 2018: ENSO atmospheric teleconnections and their response to greenhouse gas forcing. Rev. Geophys., 56, 185206, https://doi.org/10.1002/2017RG000568.

    • Search Google Scholar
    • Export Citation
  • Yung, C. K., and R. M. Holmes, 2023: On the contribution of transient diabatic processes to ocean heat transport and temperature variability. J. Phys. Oceanogr., 53, 29332951, https://doi.org/10.1175/JPO-D-23-0046.1.

    • Search Google Scholar
    • Export Citation
  • Zhang, R.-H., F. Tian, and X. Wang, 2018: Ocean chlorophyll-induced heating feedbacks on ENSO in a coupled ocean physics–biology model forced by prescribed wind anomalies. J. Climate, 31, 18111832, https://doi.org/10.1175/JCLI-D-17-0505.1.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 604 604 142
Full Text Views 195 195 64
PDF Downloads 243 243 85