Meridional Circulation Cells and the Source Waters of the Pacific Equatorial Undercurrent

Lu, Pingping; McCreary, Julian P.; Klinger, Barry A.

doi:10.1175/1520-0485(1998)028<0062:mccats>2.0.co;2

Cited by 125 publications

(111 citation statements)

References 47 publications

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“…In addition to model geometry, potential biases in model physics could affect the comparison with observations as well. For example, McCreary and Lu (1994) and Lu et al (1998) found that the PV ridge in a layer model tends to be too strong and causes an interior ocean equatorward flow that is too weak. In addition, differences can arise because of the sensitivity of models to the specification of mixing parameterizations.…”

Section: Model Limitationsmentioning

confidence: 99%

Recent Changes in the Pacific Subtropical Cells Inferred from an Eddy-Resolving Ocean Circulation Model*

Cheng

McPhaden

Zhang

et al. 2007

Journal of Physical Oceanography

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In this study the subtropical cells (STC) in the Pacific Ocean are analyzed using an eddy-resolving ocean general circulation model driven by atmospheric forcing for the years 1992-2003. In particular, the authors seek to identify decadal changes in the STCs in the model and to compare them with observations in order to understand the consequences of such changes for the equatorial ocean heat and mass budgets. The simulation shows a trend toward increasing pycnocline volume transport at 9°N and 9°S across the basin from 1992 to 2003. This increase [4.9 Ϯ 1.0 Sv (Sv ϵ 10 6 m 3 s Ϫ1)] is in qualitative agreement with observations and is attributed primarily to changes in the interior ocean transport, which are partially compensated by opposing western boundary transports. The subtropical meridional volume transport convergence anomalies in the model pycnocline are found to be consistent with anomalous volume transports in both the observed and modeled Equatorial Undercurrent, as well as with the magnitude of simulated anomalous upwelling transport at the base of the mixed layer in the eastern Pacific. As a result of the increased circulation intensity, heat transport divergence through the lateral boundaries of the tropical control volume (defined as the region between 9°N and 9°S, and from the surface to ϭ 25.3 isopycnal) increases, leading to a cooling of the tropical upper ocean despite the fact that net surface heat flux into the control volume has increased in the same time. As such, these results suggest that wind-driven changes in ocean transports associated with the subtropical cells play a central role in regulating tropical Pacific climate variability on decadal time scales.

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Section: Model Limitationsmentioning

confidence: 99%

Recent Changes in the Pacific Subtropical Cells Inferred from an Eddy-Resolving Ocean Circulation Model*

Cheng

McPhaden

Zhang

et al. 2007

Journal of Physical Oceanography

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“…Our picture of these tropical cells (TCs) is derived primarily from models (Lu et al 1998;Hazeleger et al 2001;Brown et al 2007a,b), which are poorly constrained by observations. These shallow cells are characterized by strong equatorial upwelling, near-surface wind-driven poleward divergence, downwelling near the northern and southern boundaries of the cold tongue, and equatorial convergence of geostrophic flow below the surface mixed layer.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Structure of Tropical Cells in the Central Equatorial Pacific Ocean*

Perez

Kessler

2009

Journal of Physical Oceanography

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The shallow tropical cells (TCs) in the central equatorial Pacific Ocean are characterized by strong equatorial upwelling, near-surface wind-driven poleward flow, downwelling near the cold tongue boundaries, and equatorward flow below the surface mixed layer. Meridional and vertical velocity fluctuations associated with tropical instability waves (TIWs) in the central equatorial Pacific are much larger than those associated with the TCs and can modify the background circulation. OGCM experiments are used to simulate the spinup of the cells along 1408W in response to perturbed trade winds during various phases of the annual cycle. Equatorially modified versions of geostrophy and Ekman theory, and zonal filtering, are used to isolate the large-zonal-scale wind-driven response. Weakening of the trade winds in any season rapidly weakens the TCs, decreases the zonal current shear, and reduces the amplitude and propagation speed of the TIWs. In boreal fall and winter, when the background TCs and TIWs are seasonally strong, the ocean response is equatorially asymmetric (stronger flows north of the equator) and there is evidence of rectification by the modified TIWs onto the TCs. The linear equatorially modified Ekman solutions largely explain the meridional structure and temporal evolution of the anomalous ageostrophic response in the TCs. In fall and winter, however, deviations from the modified Ekman solutions were attributed to interactions with the background TCs and TIWs. An observing system able to quantify the relative contributions of these two processes to the seasonally varying equatorial asymmetry of background circulation would require fine meridional and temporal sampling.

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“…The so-called subtropical cells (STCs) are shallow meridional overturning cells with an upwelling at the equator, a poleward Ekman transport at the surface, subduction in the subtropics and an equatorward return flow within the thermocline (McCreary and Lu 1994;Liu 1994). The equatorial upwelling is partly balanced by downwelling within the Tropics (at about 5°S and 5°N), forming relatively narrow recirculation cells that are referred to as tropical cells (TCs; Lu et al 1998). In the Atlantic, an STC mainly exists in the Southern Hemisphere.…”

Section: Introductionmentioning

confidence: 99%

Influence of El Niño on the Upper-Ocean Circulation in the Tropical Atlantic Ocean

Lohmann

Latif²

2007

Journal of Climate

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This study investigates the influence of El Niño on the upper-ocean circulation in the tropical Atlantic Ocean (via changes in the Atlantic trade winds) by analyzing observed sea surface temperature (SST) together with an ocean general circulation model integration forced by the NCEP-NCAR reanalysis. During periods with anomalously warm (cold) eastern equatorial Pacific SST, the southern Atlantic tropical cell is strengthened (weakened). The difference of the cell strength between El Niño and La Niña years is about 20% of the mean cell strength. However, the variability of the cell is not dominated by the remote forcing from the eastern equatorial Pacific but seems to be caused by intrinsic tropical Atlantic variability. A strengthening (weakening) for periods with anomalously warm (cold) eastern equatorial Pacific SST is also found for the zonal surface and subsurface currents. TOPEX/Poseidon altimetry data are used to validate the results based on the OGCM integration.

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Meridional Circulation Cells and the Source Waters of the Pacific Equatorial Undercurrent

Cited by 125 publications

References 47 publications

Recent Changes in the Pacific Subtropical Cells Inferred from an Eddy-Resolving Ocean Circulation Model*

Recent Changes in the Pacific Subtropical Cells Inferred from an Eddy-Resolving Ocean Circulation Model*

Three-Dimensional Structure of Tropical Cells in the Central Equatorial Pacific Ocean*

Influence of El Niño on the Upper-Ocean Circulation in the Tropical Atlantic Ocean

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