Forcing mechanisms of intraseasonal SST variability off central Peru in 2000–2008

Illig, Séréna; Dewitte, Boris; Goubanova, Katerina; Cambon, Gildas; Boucharel, Julien; Monetti, Florian; Romero, Carlos; Purca, Sara; Flores, Roberto

doi:10.1002/2013jc009779

Cited by 32 publications

(59 citation statements)

References 82 publications

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“…Despite the fact that the northern OMZ is embedded in the equatorial wave guide, it can be ruled out that the seasonal cycle in DO eddy flux is strongly linked to the intraseasonal long equatorial waves since the intraseasonal Kelvin wave activity tends to peak in austral summer (Illig et al, 2014). The boundary forcing sensitivity model experiments of Echevin et al (2011) also suggest that the enhanced mesoscale activity observed off northern Peru during winter would be related to internal variability or local wind stress rather than being connected to the equatorial Kelvin wave activity.…”

Section: Discussionmentioning

confidence: 99%

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

et al. 2016

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Abstract. In addition to being one of the most productive upwelling systems, the oceanic region off Peru is embedded in one of the most extensive oxygen minimum zones (OMZs) of the world ocean. The dynamics of the OMZ off Peru remain uncertain, partly due to the scarcity of data and to the ubiquitous role of mesoscale activity on the circulation and biogeochemistry. Here we use a high-resolution coupled physical/biogeochemical model simulation to investigate the seasonal variability of the OMZ off Peru. The focus is on characterizing the seasonal cycle in dissolved O 2 (DO) eddy flux at the OMZ boundaries, including the coastal domain, viewed here as the eastern boundary of the OMZ, considering that the mean DO eddy flux in these zones has a significant contribution to the total DO flux. The results indicate that the seasonal variations of the OMZ can be interpreted as resulting from the seasonal modulation of the mesoscale activity. Along the coast, despite the increased seasonal low DO water upwelling, the DO peaks homogeneously over the water column and within the Peru Undercurrent (PUC) in austral winter, which results from mixing associated with the increase in both the intraseasonal wind variability and baroclinic instability of the PUC. The coastal ocean acts therefore as a source of DO in austral winter for the OMZ core, through eddy-induced offshore transport that is also shown to peak in austral winter. In the open ocean, the OMZ can be divided vertically into two zones: an upper zone above 400 m, where the mean DO eddy flux is larger on average than the mean seasonal DO flux and varies seasonally, and a lower part, where the mean seasonal DO flux exhibits verticalzonal propagating features that share similar characteristics than those of the energy flux associated with the annual extratropical Rossby waves. At the OMZ meridional boundaries where the mean DO eddy flux is large, the DO eddy flux has also a marked seasonal cycle that peaks in austral winter (spring) at the northern (southern) boundary. In the model, the amplitude of the seasonal cycle is 70 % larger at the southern boundary than at the northern boundary. Our results suggest the existence of distinct seasonal regimes for the ventilation of the OMZ by eddies at its boundaries. Implications for understanding the OMZ variability at longer timescales are discussed.

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Section: Discussionmentioning

confidence: 99%

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

et al. 2016

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“…Regarding intraseasonal variability (Figure b), the realism of the model is reduced compared to interannual timescales, with still a fair agreement with observations. Since the ISKw activity is modulated at seasonal [ Illig et al ., ] and interannual [ Dewitte et al ., ] timescales, the validation of intraseasonal variability over the relative long record used here is a rather stringent test. The dispersion of the annual correlation is indicated in Figure b that shows that the correlation can reach up to 0.7 in the western Pacific for some specific periods.…”

Section: Methodsmentioning

confidence: 99%

The Central Pacific El Niño intraseasonal Kelvin wave

2014

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In this study, we document and interpret the characteristics of the IntraSeasonal Kelvin wave (ISKw) in the Pacific over the 1989-2011 period, based on observations, a linear model, and the outputs of an Ocean General Circulation Model (OGCM). We focus on the wave activity during the Central Pacific (CP) El Niño events contrasting with the extraordinary El Niño of 1997/1998. We find that the ISKw activity is enhanced in Austral summer (spring) in the central Pacific (west of 120 W) during CP El Niño events. The linear model experiment indicates that the Austral summer peak is wind-forced, while the Austral spring peak is not and consequently results from nonlinear processes. In addition, a strong dissipation of the ISKws is observed east of 120 W which cannot be accounted for by a linear model using a Rayleigh friction. A vertical and horizontal mode decomposition of the OGCM simulation further confirms the sharp changes in characteristics of the ISKws as well as the reflection of the latter into first-meridional Rossby wave at the longitude where the maximum zonal gradient of the thermocline is found (120 W). Our analysis suggests that the confinement of CP El Niño warming in the central Pacific may result from the reinforcement of the zonal gradient in stratification associated with the La Niña-like conditions since the late of the 1990s, leading to scattering of the energy of the ISKws in the eastern Pacific.

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“…Off central Peru, Illig et al . [] show that the remote equatorial forcing only accounts for ∼20% of the intraseasonal SST variability.…”

Section: Model Setupmentioning

confidence: 99%

Interannual variability of the subsurface eddy field in the Southeast Pacific

Combes

Hormazábal

Lorenzo

2015

J. Geophys. Res. Oceans

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The Southeast Pacific, which encompasses the coasts of Peru and Chile, is one of the world's most productive regions resulting principally from the upwelling of subsurface nutrient-rich waters. Over the satellite altimetry era, there have been numerous evidence that surface mesoscale eddies play an important role in the offshore transport of rich coastal waters, but it has been only recently that few observational/numerical studies have highlighted the importance of the subsurface eddies. The eddy field variability is explored using the results of a high-resolution model experiment from 1979 to 2012. The model results indicate an asymmetry of the surface and subsurface eddy fields. While surface-intensified cyclones are slightly more frequent than anticyclones, the subsurface field is dominated by anticyclones (IntrathermoclineEddies; ITEs), triggered by the instability of the subsurface Peru Chile undercurrent (PCUC). Composite maps are consistent with in situ observations. ITEs are associated with maximum vorticity around 150-200 m depth, warmer and more saline core, characteristic of the equatorial subsurface water from the PCUC. We find that the variability of the ITEs is significantly correlated with the ENSO equatorial signal. During strong El Niño events (e.g., 1982; 1998), we find that while the PCUC transport increases, the volume of coastal waters transported by ITEs however decreases during those periods. We find that the relaxation of the isopycnals along the coast during El Niño events leads to weakened baroclinic instability and to a decrease of the ITEs transport.

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Forcing mechanisms of intraseasonal SST variability off central Peru in 2000–2008

Cited by 32 publications

References 82 publications

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

The Central Pacific El Niño intraseasonal Kelvin wave

Interannual variability of the subsurface eddy field in the Southeast Pacific

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