Eddies and Tropical Instability Waves in the eastern tropical Pacific: A review

Willett, Cynthia S.; Leben, R. R.; Lavín, Miguel F.

doi:10.1016/j.pocean.2006.03.010

Cited by 187 publications

(155 citation statements)

References 79 publications

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“…Tropical instability waves (TIWs) are a phenomenon in which the interface between areas of warm and cold Sea Surface Temperatures (SST) near the equator forms a regular pattern of westward propagating waves [Legeckis and Reverdin, 1987;Chelton et al, 2000]. They are caused by barotropic and baroclinic instability associated with the meridional and vertical shear between the westward-flowing South Equatorial Current and the eastward flowing Equatorial Undercurrent and Equatorial Countercurrent Grodsky et al, 2005;Willett et al, 2006]. The shear at the northern edge of the cold tongues is stronger than at the southern edge [Jochum and Murtugudde, 2006], resulting in stronger TIWs in the north.…”

Section: Introductionmentioning

confidence: 99%

SMOSSea Surface Salinity signals of tropical instability waves

Yin

Boutin

Reverdin

et al. 2014

J. Geophys. Res. Oceans

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Section: Introductionmentioning

confidence: 99%

SMOSSea Surface Salinity signals of tropical instability waves

Yin

Boutin

Reverdin

et al. 2014

J. Geophys. Res. Oceans

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“…While the explanation for the detailed structure of the oceans' response to ENSO in the NETP is not resolved, especially the large thermocline anomalies in the vicinity of Papagayo, it may well involve ocean eddies, which are prominent west of Central America (see review by Willett et al 2006). Palacios and Bograd (2005) found considerable interannual variability in eddy activity, with more eddies of greater intensity and longevity during El Niñ o relative to La Niñ a years over the period 1992-2004.…”

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confidence: 99%

ENSO’s Impact on the Gap Wind Regions of the Eastern Tropical Pacific Ocean*

et al. 2012

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The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979-2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niñ o (La Niñ a) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niñ o in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niñ o events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not.

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“…A novel result of this study is that the ageostrophic Ekman currents depend, not only upon the wind, but also upon the strength and orientation of the front relative to the wind. Observations during the passage of tropical instability waves (Willett et al 2006) offer an opportunity to test this idea since the orientation of the front varies over the course of a wave, while the orientation of the wind is relatively steady.…”

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confidence: 99%

Near-Surface Shear Flow in the Tropical Pacific Cold Tongue Front*

Cronin

Kessler

2009

Journal of Physical Oceanography

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Near-surface shear in the Pacific cold tongue front at 28N, 1408W was measured using a set of five moored current meters between 5 and 25 m for nine months during 2004-05. Mean near-surface currents were strongly westward and only weakly northward (;3 cm s 21). Mean near-surface shear was primarily westward and, thus, oriented to the left of the southeasterly trades. When the southwestward geostrophic shear was subtracted from the observed shear, the residual ageostrophic currents relative to 25 m were northward and had an Ekman-like spiral, in qualitative agreement with an Ekman model modified for regions with a vertically uniform front. According to this ''frontal Ekman'' model, the ageostrophic Ekman spiral is forced by the portion of the wind stress that is not balanced by the surface geostrophic shear. Analysis of a composite tropical instability wave (TIW) confirms that ageostrophic shear is minimized when winds blow along the front, and strengthens when winds blow oblique to the front. Furthermore, the magnitude of the near-surface shear, both in the TIW and diurnal composites, was sensitive to near-surface stratification and mixing. A diurnal jet was observed that was on average 12 cm s 21 stronger at 5 m than at 25 m, even though daytime stratification was weak. The resulting Richardson number indicates that turbulent viscosity is larger at night than daytime and decreases with depth. A ''generalized Ekman'' model is also developed that assumes that viscosity becomes zero below a defined frictional layer. The generalized model reproduces many of the features of the observed mean shear and is valid both in frontal regions and at the equator.

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Eddies and Tropical Instability Waves in the eastern tropical Pacific: A review

Cited by 187 publications

References 79 publications

SMOSSea Surface Salinity signals of tropical instability waves

SMOSSea Surface Salinity signals of tropical instability waves

ENSO’s Impact on the Gap Wind Regions of the Eastern Tropical Pacific Ocean*

Near-Surface Shear Flow in the Tropical Pacific Cold Tongue Front*

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