Editorial Type:
Article
Article Type:
Research Article

Mean Circulation and Variability of the Tropical Atlantic during 1952–2001 in the GECCO Assimilation Fields

Benjamin Rabe IFM-GEOMAR, Leibniz-Institut für Meereswissenschaften an der Universität Kiel, Kiel, Germany

Search for other papers by Benjamin Rabe in
Current site
Google Scholar
PubMed Close
,
Friedrich A. Schott IFM-GEOMAR, Leibniz-Institut für Meereswissenschaften an der Universität Kiel, Kiel, Germany

Search for other papers by Friedrich A. Schott in
Current site
Google Scholar
PubMed Close
, and
Armin Köhl Institut für Meereskunde, Zentrum für Meeres und Klimaforschung, Universität Hamburg, Hamburg, Germany

Search for other papers by Armin Köhl in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Jan 2008
DOI:
https://doi.org/10.1175/2007JPO3541.1
Page(s):
177–192
Restricted access

Abstract

The shallow subtropical–tropical cells (STC) of the Atlantic Ocean have been studied from the output fields of a 50-yr run of the German partner of the Estimating the Circulation and Climate of the Ocean (GECCO) consortium assimilation model. Comparison of GECCO with time-mean observational estimates of density and meridional currents at 10°S and 10°N, which represent the boundaries between the tropics and subtropics in GECCO, shows good agreement in transports of major currents. The variability of the GECCO wind stress in the interior at 10°S and 10°N remains consistent with the NCEP forcing, although temporary changes can be large. On pentadal and longer time scales, an STC loop response is found between the poleward Ekman divergence and STC-layer convergence at 10°S and 10°N via the Equatorial Undercurrent (EUC) at 23°W, where the divergence leads the EUC and the convergence, suggesting a “pulling” mechanism via equatorial upwelling. The divergence is also associated with changes in the eastern equatorial upper-ocean heat content. Within the STC layer, partial compensation of the western boundary current (WBC) and the interior occurs at 10°S and 10°N. For the meridional overturning circulation (MOC) at 10°S it is found that more than one-half of the variability in the upper limb can be explained by the WBC. The explained MOC variance can be increased to 85% by including the geostrophic (Sverdrup) part of the wind-driven transports.

Corresponding author address: Benjamin Rabe, Climate Sciences, Alfred-Wegener-Institute for Polar and Marine Research, Bussestr. 24, Postfach 120161, 27515 Bremerhaven, Germany. Email: benjamin.rabe@awi.de

Abstract

The shallow subtropical–tropical cells (STC) of the Atlantic Ocean have been studied from the output fields of a 50-yr run of the German partner of the Estimating the Circulation and Climate of the Ocean (GECCO) consortium assimilation model. Comparison of GECCO with time-mean observational estimates of density and meridional currents at 10°S and 10°N, which represent the boundaries between the tropics and subtropics in GECCO, shows good agreement in transports of major currents. The variability of the GECCO wind stress in the interior at 10°S and 10°N remains consistent with the NCEP forcing, although temporary changes can be large. On pentadal and longer time scales, an STC loop response is found between the poleward Ekman divergence and STC-layer convergence at 10°S and 10°N via the Equatorial Undercurrent (EUC) at 23°W, where the divergence leads the EUC and the convergence, suggesting a “pulling” mechanism via equatorial upwelling. The divergence is also associated with changes in the eastern equatorial upper-ocean heat content. Within the STC layer, partial compensation of the western boundary current (WBC) and the interior occurs at 10°S and 10°N. For the meridional overturning circulation (MOC) at 10°S it is found that more than one-half of the variability in the upper limb can be explained by the WBC. The explained MOC variance can be increased to 85% by including the geostrophic (Sverdrup) part of the wind-driven transports.

Corresponding author address: Benjamin Rabe, Climate Sciences, Alfred-Wegener-Institute for Polar and Marine Research, Bussestr. 24, Postfach 120161, 27515 Bremerhaven, Germany. Email: benjamin.rabe@awi.de

Save
Cover Journal of Physical Oceanography
Journal of Physical Oceanography

  • Brandt, P., F. A. Schott, C. Provost, A. Kartavtseff, V. Hormann, B. Bourles, and J. Fischer, 2006: Circulation in the central equatorial Atlantic: Mean and intraseasonal to seasonal variability. Geophys. Res. Lett., 33 .L07609, doi:10.1029/2005GL025498.

    • Search Google Scholar
    • Export Citation

  • Bretherton, C. S., M. Widmann, V. P. Dymnikov, J. M. Wallace, and I. Bladé, 1999: The effective number of spatial degrees of freedom of a time-varying field. J. Climate, 12 , 1990–2009.

    • Search Google Scholar
    • Export Citation

  • Capotondi, A., M. A. Alexander, C. Deser, and M. J. McPhaden, 2005: Anatomy and decadal evolution of the Pacific subtropical–tropical cells (STCs). J. Climate, 18 , 3739–3758.

    • Search Google Scholar
    • Export Citation

  • Cheng, W., M. J. McPhaden, D. Zhang, and E. J. Metzger, 2007: Recent changes in the Pacific subtropical cells inferred from an eddy-resolving ocean circulation model. J. Phys. Oceanogr., 37 , 1340–1356.

    • Search Google Scholar
    • Export Citation

  • Chereskin, T. K., and D. Roemmich, 1991: A comparison of measured and wind-derived Ekman transport at 11°N in the Atlantic Ocean. J. Phys. Oceanogr., 21 , 869–878.

    • Search Google Scholar
    • Export Citation

  • Foltz, G. R., S. A. Grodsky, J. A. Carton, and M. J. McPhaden, 2003: Seasonal mixed layer heat budget of the tropical Atlantic Ocean. J. Geophys. Res., 108 .3146, doi:10.1029/2002JC001584.

    • Search Google Scholar
    • Export Citation

  • Fratantoni, D. M., W. E. Johns, T. L. Townsend, and H. E. Hurlburt, 2000: Low-latitude circulation and mass transport pathways in a model of the tropical Atlantic Ocean. J. Phys. Oceanogr., 30 , 1944–1966.

    • Search Google Scholar
    • Export Citation

  • Ganachaud, A., 2003: Large-scale mass transports, water mass formation, and diffusivities estimated from World Ocean Circulation Experiment (WOCE) hydrographic data. J. Geophys. Res., 108 .3213, doi:10.1029/2002JC001565.

    • Search Google Scholar
    • Export Citation

  • Giarolla, E., P. Nobre, M. Malagutti, and L. P. Pezzi, 2005: The Atlantic Equatorial Undercurrent: PIRATA observations and simulations with GFDL Modular Ocean Model at CPTEC. Geophys. Res. Lett., 32 .L10617, doi:10.1029/2004GL022206.

    • Search Google Scholar
    • Export Citation

  • Gill, A. E., 1982: Atmosphere–Ocean Dynamics. Academic Press, 662 pp.

  • Grodsky, S. A., and J. A. Carton, 2002: Surface drifter pathways originating in the equatorial Atlantic cold tongue. Geophys. Res. Lett., 29 , 62–65.

    • Search Google Scholar
    • Export Citation

  • Hazeleger, W., and S. Drijfhout, 2006: Subtropical cells and meridional overturning circulation pathways in the tropical Atlantic. J. Geophys. Res., 111 .C03013, doi:10.1029/2005JC002942.

    • Search Google Scholar
    • Export Citation

  • Hüttl, S., and C. W. Böning, 2006: Mechanisms of decadal variability in the shallow subtropical-tropical circulation of the Atlantic Ocean: A model study. J. Geophys. Res., 111 .C07011, doi:10.1029/2005JC003414.

    • Search Google Scholar
    • Export Citation

  • Inui, T., A. Lazar, P. Malanotte-Rizzoli, and A. Busalacchi, 2002: Wind stress effects on subsurface pathways from the subtropical to tropical Atlantic. J. Phys. Oceanogr., 32 , 2257–2276.

    • Search Google Scholar
    • Export Citation

  • Jochum, M., and P. Malanotte-Rizzoli, 2001: Influence of the meridional overturning circulation on tropical–subtropical pathways. J. Phys. Oceanogr., 31 , 1313–1323.

    • Search Google Scholar
    • Export Citation

  • Johns, W. E., T. N. Lee, R. C. Beardsley, J. Candela, R. Limeburger, and B. Castro, 1998: Annual cycle and variability of the North Brazil Current. J. Phys. Oceanogr., 28 , 103–128.

    • Search Google Scholar
    • Export Citation

  • Köhl, A., D. Dommenget, K. Ueyoshi, and D. Stammer, 2006: The Global ECCO 1952 to 2001 ocean synthesis. The ECCO Report Series, Tech. Rep. 40, 44 pp. [Available online at http://www.ecco-group.org/pdfs/reports/report_40.pdf.].

  • Köhl, A., D. Stammer, and B. Cornuelle, 2007: Interannual to decadal changes in the ECCO global synthesis. J. Phys. Oceanogr., 37 , 313–337.

    • Search Google Scholar
    • Export Citation

  • Kröger, J., A. J. Busalacchi, J. Ballabrera-Poy, and P. Malanotte-Rizzoli, 2005: Decadal variability of shallow cells and equatorial sea surface temperature in a numerical model of the Atlantic. J. Geophys. Res., 110 .C12003, doi:10.1029/2004JC002703.

    • Search Google Scholar
    • Export Citation

  • Lazar, A., T. Inui, P. Malanotte-Rizzoli, A. J. Busalacchi, L. Wang, and R. Murtugudde, 2002: Seasonality of the ventilation of the tropical Atlantic thermocline in an ocean general circulation model. J. Geophys. Res., 107 .3104, doi:10.1029/2000JC000667.

    • Search Google Scholar
    • Export Citation

  • Lee, T., and J. Marotzke, 1998: Seasonal cycles of meridional overturning and heat transport of the Indian Ocean. J. Phys. Oceanogr., 28 , 962–983.

    • Search Google Scholar
    • Export Citation

  • Lee, T., and I. Fukumori, 2003: Interannual-to-decadal variations of tropical-subtropical exchange in the Pacific Ocean: Boundary versus interior pycnocline transports. J. Climate, 16 , 4022–4041.

    • Search Google Scholar
    • Export Citation

  • Lee, T. N., W. E. Johns, R. J. Zantopp, and E. R. Fillenbaum, 1996: Moored observations of western boundary current variability and thermohaline circulation at 26.5°N in the subtropical North Atlantic. J. Phys. Oceanogr., 26 , 962–983.

    • Search Google Scholar
    • Export Citation

  • Liu, Z., S. G. H. Philander, and R. C. Pacanowski, 1994: A GCM study of tropical–subtropical upper-ocean water exchange. J. Phys. Oceanogr., 24 , 2606–2623.

    • Search Google Scholar
    • Export Citation

  • Lumpkin, R., and K. Speer, 2003: Large-scale vertical and horizontal circulation in the North Atlantic Ocean. Deep-Sea Res. I, 33 , 1902–1920.

    • Search Google Scholar
    • Export Citation

  • Lumpkin, R., and S. L. Garzoli, 2005: Near-surface circulation in the tropical Atlantic Ocean. Deep-Sea Res. I, 52 , 495–518.

  • Malanotte-Rizzoli, P., P. K. Hedstrom, H. Arango, and D. B. Haidvogel, 2000: Water mass path-ways between the subtropical and tropical ocean in a climatological simulation of the North Atlantic ocean circulation. Dyn. Atmos. Oceans, 32 , 331–371.

    • Search Google Scholar
    • Export Citation

  • Marshall, J., A. Adcroft, C. Hill, L. Perelman, and C. Heisey, 1997: A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers. J. Geophys. Res., 102 , 5753–5766.

    • Search Google Scholar
    • Export Citation

  • McCreary, J. P., and P. Lu, 1994: Interaction between the subtropical and equatorial ocean circulations: The subtropical cell. J. Phys. Oceanogr., 24 , 466–497.

    • Search Google Scholar
    • Export Citation

  • McPhaden, M. J., and D. X. Zhang, 2002: Slowdown of the meridional overturning circulation in the upper Pacific Ocean. Nature, 415 , 603–608.

    • Search Google Scholar
    • Export Citation

  • McPhaden, M. J., and D. Zhang, 2004: Pacific Ocean circulation rebounds. Geophys. Res. Lett., 31 .L18301, doi:10.1029/2004GL020727.

  • Molinari, R. L., S. Bauer, D. Snowden, G. C. Johnson, B. Bourles, Y. Gouriou, and H. Mercier, 2003: A comparison of kinematic evidence for tropical cells in the Atlantic and Pacific Oceans. Interhemispheric Water Exchange in the Atlantic Ocean, G. J. Goni, and P. Malanotte-Rizzoli, Eds., Elsevier Oceanographic Series, Vol. 68, Elsevier, 269–286.

    • Search Google Scholar
    • Export Citation

  • Schott, F. A., J. P. McCreary, and G. C. Johnson, 2004: Earth climate: The ocean–atmosphere interaction. Shallow Overturning Circulations of the Tropical-Subtropical Oceans, Geophys. Monogr., Vol. 147, Amer. Geophys. Union, 231–304.

    • Search Google Scholar
    • Export Citation

  • Schott, F. A., M. Dengler, R. Zantopp, L. Stramma, J. Fischer, and P. Brandt, 2005: The shallow and deep western boundary circulation of the South Atlantic at 5°–11°S. J. Phys. Oceanogr., 35 , 2031–2053.

    • Search Google Scholar
    • Export Citation

  • Schott, F. A., W. Wang, and D. Stammer, 2007: Variability of the Pacific subtropical cells in the 50-year ECCO assimilation. Geophys. Res. Lett., 34 .L05604, doi:10.1029/2006GL028478.

    • Search Google Scholar
    • Export Citation

  • Schouten, M. W., R. P. Matano, and T. P. Strub, 2005: A description of the seasonal cycle of the equatorial Atlantic from altimeter data. Deep-Sea Res. I, 52 , 477–493.

    • Search Google Scholar
    • Export Citation

  • Sime, L. C., D. P. Stevens, K. J. Heywood, and K. I. C. Oliver, 2006: A decomposition of the Atlantic meridional overturning. J. Phys. Oceanogr., 36 , 2253–2270.

    • Search Google Scholar
    • Export Citation

  • Snowden, D. P., and R. L. Molinari, 2003: Subtropical cells in the Atlantic Ocean: An observational summary. Interhemispheric Water Exchange in the Atlantic Ocean, G. J. Goni, and P. Malanotte-Rizzoli, Eds., Elsevier Oceanographic Series, Vol. 68, Elsevier, 287–312.

    • Search Google Scholar
    • Export Citation

  • Stammer, D., K. Ueyoshi, A. Köhl, W. G. Large, S. A. Josey, and C. Wunsch, 2004: Estimating air-sea fluxes of heat, freshwater, and momentum through global ocean data assimilation. J. Geophys. Res., 109 .C05023, doi:10.1029/2003JC002082.

    • Search Google Scholar
    • Export Citation

  • Stramma, L., and M. England, 1999: On the water masses and mean circulation of the South Atlantic Ocean. J. Geophys. Res., 104 , 20863–20883.

    • Search Google Scholar
    • Export Citation

  • Stramma, L., and F. Schott, 1999: The mean flow field of the tropical Atlantic Ocean. Deep-Sea Res. II, 46 , 279–303.

  • Talley, L. D., J. L. Reid, and P. E. Robbins, 2003: Data-based meridional overturning streamfunctions for the global oceans. J. Climate, 16 , 3213–3226.

    • Search Google Scholar
    • Export Citation

  • Wilson, W. D., E. Johns, and R. L. Molinari, 1994: Upper layer circulation in the western tropical North Atlantic Ocean during August 1989. J. Geophys. Res., 99 , 22513–22523.

    • Search Google Scholar
    • Export Citation

  • Wunsch, C., 1996: The Ocean Circulation Inverse Problem. Cambridge University Press, 437 pp.

  • Zhang, D., M. J. McPhaden, and W. E. Johns, 2003: Observational evidence for flow between the subtropical and tropical Atlantic: The Atlantic tropical cells. J. Phys. Oceanogr., 33 , 1783–1797.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 613 90 6
PDF Downloads 116 30 4