Seasonal Variability of the South Equatorial Current Bifurcation in the Atlantic Ocean: A Numerical Study

Journal of Physical Oceanography - Tập 37 Số 1 - Trang 16-30 - 2007
Regina R. Rodrigues1, Lewis M. Rothstein1, Mark Wimbush1
1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island

Tóm tắt

Abstract In this study, a reduced-gravity, primitive equation OGCM is used to investigate the seasonal variability of the bifurcation of the South Equatorial Current (SEC) into the Brazil Current (BC) to the south and the North Brazil Undercurrent/Current (NBUC/NBC) system to the north. Annual mean meridional velocity averaged within a 2° longitude band off the South American coast shows that the SEC bifurcation occurs at about 10°–14°S near the surface, shifting poleward with increasing depth, reaching 27°S at 1000 m, in both observations and model. The bifurcation latitude reaches its southernmost position in July (∼17°S in the top 200 m) and its northernmost position in November (∼13°S in the top 200 m). The model results show that most of the seasonal variability of the bifurcation latitude in the upper thermocline is associated with changes in the local wind stress curl due to the annual north–south excursion of the marine ITCZ complex. As the SEC bifurcation latitude moves south (north) the NBUC transport increases (decreases) and the BC transport decreases (increases). The remote forcing (i.e., westward propagation of anomalies) appears to have a smaller impact on the seasonal variability of the bifurcation in the upper thermocline.

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Tài liệu tham khảo

Blanke, 1999, Warm water paths in the equatorial Atlantic as diagnosed with a general circulation model., J. Phys. Oceanogr., 29, 2753, 10.1175/1520-0485(1999)029<2753:WWPITE>2.0.CO;2

Boebel, 1999, The intermediate depth circulation of the western South Atlantic., Geophys. Res. Lett., 26, 3329, 10.1029/1999GL002355

Campos, 1995, Water mass characteristics and geostrophic circulation in the South Brazil Bight: Summer of 1991., J. Geophys. Res., 100, 18537, 10.1029/95JC01724

Chen, 1994, The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacific Ocean., J. Geophys. Res., 99, 20345, 10.1029/94JC01621

Chen, 1994, A hybrid vertical mixing scheme and its application to tropical ocean models., J. Phys. Oceanogr., 24, 2156, 10.1175/1520-0485(1994)024<2156:AHVMSA>2.0.CO;2

Conkright, M. E., R. A.Locarnini, H. E.Garcia, T. D.O’Brien, T. P.Boyer, C.Stephens, and J. I.Antonov, 2002: World Ocean Atlas 2001: Objective Analyses, Data Statistics, and Figures. CD-ROM Documentation. National Oceanographic Data Center, 17 pp.

Curry, R. G. , 1996: Hydrobase: A database of hydrographic stations and tools for climatological analysis. Woods Hole Oceanographic Institute Tech. Rep. 96-01, 50 pp.

da Silva, 1994, Algorithms and Procedures.

da Silva, M. P., and P.Chang, 2004: Seasonal variation of the subtropical/tropical pathways in the Atlantic Ocean from a Ocean Data Assimilation Experiment. Earth’s Climate: The Ocean–Atmosphere Interaction, Geophys. Monogr., Vol. 147, Amer. Geophys. Union, 305–318.

da Silveira, 1994, On the origins of the North Brazil Current., J. Geophys. Res., 99, 22501, 10.1029/94JC01776

Davis, 1976, Predictability of sea surface temperature and sea level pressure anomalies over the North Pacific Ocean., J. Phys. Oceanogr., 6, 249, 10.1175/1520-0485(1976)006<0249:POSSTA>2.0.CO;2

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

Garfield III, N. , 1990: The Brazil Current at subtropical latitudes. Ph.D. dissertation, University of Rhode Island, 132 pp.

Gent, 1989, A reduced gravity, primitive equation model of upper equatorial ocean., J. Comput. Phys., 81, 444, 10.1016/0021-9991(89)90216-7

Giese, 1993, Surface heat flux parameterizations and tropical Pacific sea surface temperature simulations., J. Geophys. Res., 98, 6979, 10.1029/93JC00323

Ginis, 1998, Design of a multiply nested primitive equation ocean model., Mon. Wea. Rev., 126, 1054, 10.1175/1520-0493(1998)126<1054:DOAMNP>2.0.CO;2

Goes, 2005, Retroflections of the North Brazil Current during February 2002., Deep-Sea Res., 52, 647, 10.1016/j.dsr.2004.10.010

Harper, 2000, Thermocline ventilation and pathways of tropical-subtropical water mass exchange., Tellus, 52A, 330, 10.3402/tellusa.v52i3.12269

Hazeleger, 2003, Sources of the equatorial undercurrent in the Atlantic in a high-resolution ocean model., J. Phys. Oceanogr., 33, 677, 10.1175/1520-0485(2003)33<677:SOTEUI>2.0.CO;2

Inui, 2002, Wind stress effects on subsurface pathways from the subtropical to tropical Atlantic., J. Phys. Oceanogr., 32, 2257, 10.1175/1520-0485(2002)032<2257:WSEOSP>2.0.CO;2

Johns, 2003, Cross-gyre transport by North Brazil Current rings., 10.1016/S0422-9894(03)80156-3

Kara, 2000, Efficient and accurate bulk parameterizations of air–sea fluxes for use in general circulation models., J. Atmos. Oceanic Technol., 17, 1421, 10.1175/1520-0426(2000)017<1421:EAABPO>2.0.CO;2

Kim, 2004, Seasonal and interannual variations of the North Equatorial Current bifurcation in a high-resolution OGCM., J. Geophys. Res., 109, 10.1029/2003JC002013

Kleeman, 1999, A mechanism for generating ENSO decadal variability., Geophys. Res. Lett., 26, 1743, 10.1029/1999GL900352

Kochurov, A. G. , 2002: The ocean response to atmospheric intraseasonal variability in the tropical Pacific Ocean. Ph.D. dissertation, University of Rhode Island, 228 pp.

Kraus, 1967, A one-dimensional model of the seasonal thermocline., Tellus, 19, 98, 10.3402/tellusa.v19i1.9753

Lazar, 2001, A model study of temperature anomaly propagation from the subtropics to Tropics within the South Atlantic thermocline., Geophys. Res. Lett., 28, 1271, 10.1029/2000GL011418

Lazar, 2002, Seasonality of the ventilation of the tropical Atlantic thermocline in an ocean general circulation model., J. Geophys. Res., 107, 10.1029/2000JC000667

Lee, 2003, Interannual-to-decadal variations of tropical–subtropical exchange in the Pacific Ocean: Boundary versus interior pycnocline transports., J. Climate, 16, 4022, 10.1175/1520-0442(2003)016<4022:IVOTEI>2.0.CO;2

Liu, 1994, A GCM study of tropical–subtropical upper-ocean water exchange., J. Phys. Oceanogr., 24, 2606, 10.1175/1520-0485(1994)024<2606:AGSOTU>2.0.CO;2

Lu, 1995, Influence of the ITCZ on the flow of thermocline water from the subtropical to the equatorial Pacific Ocean., J. Phys. Oceanogr., 25, 3076, 10.1175/1520-0485(1995)025<3076:IOTIOT>2.0.CO;2

Lumpkin, 2003, Large-scale vertical and horizontal circulation in the North Atlantic Ocean., J. Phys. Oceanogr., 33, 1902, 10.1175/1520-0485(2003)033<1902:LVAHCI>2.0.CO;2

Malanotte-Rizzoli, 2000, Water mass pathways between the subtropical and tropical ocean in a climatological simulation of the North Atlantic Ocean circulation., Dyn. Atmos. Oceans, 32, 331, 10.1016/S0377-0265(00)00051-8

McCreary, 1994, Interaction between the subtropical and equatorial ocean circulations: The subtropical cell., J. Phys. Oceanogr., 24, 466, 10.1175/1520-0485(1994)024<0466:IBTSAE>2.0.CO;2

McPhaden, 2002, Slowdown of the meridional overturning circulation in the upper Pacific Ocean., Nature, 415, 603, 10.1038/415603a

McPhaden, 2004, Pacific Ocean circulation rebounds., Geophys. Res. Lett., 31, 10.1029/2004GL020727

Meehl, 2001, Factors that affect the amplitude of El Niño in global coupled climate models., Climate Dyn., 17, 515, 10.1007/PL00007929

Metcalf, 1967, Origins of the Atlantic Equatorial Undercurrent., J. Geophys. Res., 72, 4959, 10.1029/JZ072i020p04959

Metzger, 1996, Coupled dynamics of the South China Sea, the Sulu Sea, and the Pacific Ocean., J. Geophys. Res., 101, 12331, 10.1029/95JC03861

Nonaka, 2002, Decadal variations in the subtropical cells and equatorial Pacific SST., Geophys. Res. Lett., 29, 10.1029/2001GL013717

Price, 1986, Diurnal cycling: Observations and models of the upper ocean response to diurnal heating, cooling, and wind mixing., J. Geophys. Res., 91, 8411, 10.1029/JC091iC07p08411

Qiu, 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, 12315, 10.1029/95JC03204

Qu, 2003, The bifurcation of the North Equatorial Current in the Pacific., J. Phys. Oceanogr., 33, 5, 10.1175/1520-0485(2003)033<0005:TBOTNE>2.0.CO;2

Qu, 2000, Intrusion of the North Pacific waters into the South China Sea., J. Geophys. Res., 105, 6415, 10.1029/1999JC900323

Rodrigues, R. R. , 2004: An observational and numerical study of the South Atlantic circulation. Ph.D. dissertation, University of Rhode Island, 175 pp.

Rothstein, 1998, A numerical simulation of the mean water pathways in the subtropical and tropical Pacific Ocean., J. Phys. Oceanogr., 28, 322, 10.1175/1520-0485(1998)028<0322:ANSOTM>2.0.CO;2

Schmid, 2000, Dynamics of intermediate water circulation in the subtropical South Atlantic., J. Phys. Oceanogr., 30, 3191, 10.1175/1520-0485(2000)030<3191:DOIWCI>2.0.CO;2

Schmitz, 1995, On the interbasin-scale thermohaline circulation., Rev. Geophys., 33, 151, 10.1029/95RG00879

Schott, 1995, The warm water inflow into the western tropical Atlantic boundary regime, spring 1994., J. Geophys. Res., 100, 24745, 10.1029/95JC02803

Schott, 1998, Transports and pathways of the upper-layer circulation in the western tropical Atlantic., J. Phys. Oceanogr., 28, 1904, 10.1175/1520-0485(1998)028<1904:TAPOTU>2.0.CO;2

Schott, 2002, On the boundary flow off Brazil at 5°–10°S and its connection to the interior tropical Atlantic., Geophys. Res. Lett., 29, 10.1029/2002GL014786

Stramma, 1991, Geostrophic transport of the South Equatorial Current in the Atlantic., J. Mar. Res., 49, 281, 10.1357/002224091784995864

Stramma, 1990, The South Atlantic Current., J. Phys. Oceanogr., 20, 846, 10.1175/1520-0485(1990)020<0846:TSAC>2.0.CO;2

Stramma, 1999, On the water masses and mean circulation of the South Atlantic Ocean., J. Geophys. Res., 104, 20863, 10.1029/1999JC900139

Stramma, 1999, The mean flow field of the tropical Atlantic Ocean., Deep-Sea Res., 46, 279

Stramma, 2003, Circulation, variability and near-equatorial meridional flow in the central tropical Atlantic., 10.1016/S0422-9894(03)80141-1

Talley, 2003, Shallow, intermediate, and deep overturning components of the global heat budget., J. Phys. Oceanogr., 33, 530, 10.1175/1520-0485(2003)033<0530:SIADOC>2.0.CO;2

Tsuchiya, 1994, Water-mass distributions in the western South Atlantic: A section from South Georgia Island (54°S) northward across the equator., J. Mar. Res., 52, 55, 10.1357/0022240943076759

Vivier, 1999, Direct velocity measurements in the Malvinas Current., J. Geophys. Res., 104, 21083, 10.1029/1999JC900163

Watts, 2001, Mapping abyssal current and pressure fields under the meandering Gulf Stream., J. Atmos. Oceanic Technol., 18, 1052, 10.1175/1520-0426(2001)018<1052:MACAPF>2.0.CO;2

Wienders, 2000, Circulation at the western boundary of the South and Equatorial Atlantic: Exchanges with the ocean interior., J. Mar. Res., 58, 1007, 10.1357/002224000763485782

Wilson, 1994, Upper layer circulation in the western tropical North Atlantic Ocean during August 1989., J. Geophys. Res., 99, 22513, 10.1029/94JC02066

Zhang, 2003, Observational evidence for flow between the subtropical and tropical Atlantic: The Atlantic subtropical cells., J. Phys. Oceanogr., 33, 1783, 10.1175/2408.1