Dynamics of the Pacific Subsurface Countercurrents*

McCreary, Julian P.; Lu, Pingping; Yu, Zuojun

doi:10.1175/1520-0485(2002)032<2379:dotpsc>2.0.co;2

Cited by 57 publications

(58 citation statements)

References 35 publications

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“…They are weaker, or nonexistent, in all the model solutions, most likely because of an overly viscous ocean model. This could be a serious deficiency, because these "Tsuchiya" jets are thought to be linked to the upwelling zones along the coast of South America (McCreary et al 2002).…”

Section: Discussionsupporting

confidence: 76%

Attribution and Impacts of Upper-Ocean Biases in CCSM3

2006

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The largest and potentially most important ocean near-surface biases are examined in the Community Climate System Model coupled simulation of present-day conditions. They are attributed to problems in the component models of the ocean or atmosphere, or both. Tropical biases in sea surface salinity (SSS) are associated with precipitation errors, with the most striking being a band of excess rainfall across the South Pacific at about 8°S. Cooler-than-observed equatorial Pacific sea surface temperature (SST) is necessary to control a potentially catastrophic positive feedback, involving precipitation along the equator. The strength of the wind-driven gyres and interbasin exchange is in reasonable agreement with observations, despite the generally too strong near-surface winds. However, the winds drive far too much transport through Drake Passage [Ͼ190 Sv (1 Sv ϵ 10 6 m 3 s Ϫ1)], but with little effect on SST and SSS. Problems with the width, separation, and location of western boundary currents and their extensions create large correlated SST and SSS biases in midlatitudes. Ocean model deficiencies are suspected because similar signals are seen in uncoupled ocean solutions, but there is no evidence of serious remote impacts. The seasonal cycles of SST and winds in the equatorial Pacific are not well represented, and numerical experiments suggest that these problems are initiated by the coupling of either or both wind components. The largest mean SST biases develop along the eastern boundaries of subtropical gyres, and the overall coupled model response is found to be linear. In the South Atlantic, surface currents advect these biases across much of the tropical basin. Significant precipitation responses are found both in the northwest Indian Ocean, and locally where the net result is the loss of an identifiable Atlantic intertropical convergence zone, which can be regained by controlling the coastal temperatures and salinities. Biases off South America and Baja California are shown to significantly degrade precipitation across the Pacific, subsurface ocean properties on both sides of the equator, and the seasonal cycle of equatorial SST in the eastern Pacific. These signals extend beyond the reach of surface currents, so connections via the atmosphere and subsurface ocean are implicated. Other experimental results indicate that the local atmospheric forcing is only part of the problem along eastern boundaries, with the representation of ocean upwelling another likely contributor.

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Section: Discussionsupporting

confidence: 76%

Attribution and Impacts of Upper-Ocean Biases in CCSM3

2006

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“…Intra-seasonal variability is stronger during ENSO periods. Another equatorial connection is between the subsurface Equatorial Countercurrents and the PCUC in the PCS (McCreary et al 2002;Kessler 2006;Montes et al 2010). 5 The PCUC carries equatorial waters along the slope as far south as Chile and feeds the nearshore upwelled waters, as well as the subsurface coherent vortices generated by instability (Sect.…”

Section: Depth [M]supporting

confidence: 67%

Heat balance and eddies in the Peru-Chile current system

et al. 2011

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International audienceThe Peru-Chile current System (PCS) is a region of persistent biases in global climate models. It has strong coastal upwelling, alongshore boundary currents, and mesoscale eddies. These oceanic phenomena provide essential heat transport to maintain a cool oceanic surface underneath the prevalent atmospheric stratus cloud deck, through a combination of mean circulation and eddy flux. We demonstrate these behaviors in a regional, quasi-equilibrium oceanic model that adequately resolves the mesoscale eddies with climatological forcing. The key result is that the atmospheric heating is large (>50 W m^-2) over a substantial strip >500 km wide off the coast of Peru, and the balancing lateral oceanic flux is much larger than provided by the offshore Ekman flux alone. The atmospheric heating is weaker and the coastally influenced strip is narrower off Chile, but again the Ekman flux is not sufficient for heat balance. The eddy contribution to the oceanic flux is substantial. Analysis of eddy properties shows strong surface temperature fronts and associated large vorticity, especially off Peru. Cyclonic eddies moderately dominate the surface layer, and anticyclonic eddies, originating from the nearshore poleward Peru-Chile Undercurrent (PCUC), dominate the subsurface, especially off Chile. The sensitivity of the PCS heat balance to equatorial intra-seasonal oscillations is found to be small. We demonstrate that forcing the regional model with a representative, coarse-resolution global reanalysis wind product has dramatic and deleterious consequences for the oceanic circulation and climate heat balance, the eddy heat flux in particular

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“…It is unknown how three dimensional currents affect the coastal upwelling in the SWA coastal region. McCreary et al (2002) propose that the SEUC feeds the coastal upwelling, but the role of EUC, and SEUC in affecting the coastal upwelling is unclear. Additionally, the eddy activities are suppressed by model configurations including the steady wind, high viscosities and straight coastlines, but these features are ubiquitous along real eastern oceanic boundaries and play important roles in the surface heat budget (Capet et al 2008).…”

Section: Discussionmentioning

confidence: 99%

On the warm bias along the South-West African Coast in coupled models : an oceanic perspective

Wang¹

2008

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Coupled ocean/atmosphere simulations exhibit systematic warm biases over the South West African (SWA) coastal region. Recent investigations indicate that coastal ocean dynamics may play an important role in determining the SST patterns, but none of them provide a detailed analysis. In this study, I analyze simulations produced both by coupled models and by idealized models. Then results are interpreted on the basis of a theoretical framework.Finally the conclusion is reached that the insufficient resolution of the ocean component in the coupled model is responsible for the warm biases over the SWA coastal region. The coarse resolution used in the ocean model has an artificially stretched coastal side-wall boundary layer, which induces a smaller upwelling velocity in the boundary layer. The vertical heat transport decreases even when the volume transport is unchanged because of its nonlinear relationship with the magnitude of the upwelling velocity. Based on the scaling of the idealized model simulations, a simplified calculation shows that the vertical heat transport is inversely proportional to the zonal resolution over the coastal region. Therefore, increasing the horizontal resolution can considerably improve the coastal SST simulation, and better resolve the coastal dynamics.

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Dynamics of the Pacific Subsurface Countercurrents*

Cited by 57 publications

References 35 publications

Attribution and Impacts of Upper-Ocean Biases in CCSM3

Attribution and Impacts of Upper-Ocean Biases in CCSM3

Heat balance and eddies in the Peru-Chile current system

On the warm bias along the South-West African Coast in coupled models : an oceanic perspective

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