Reflection of equatorial Kelvin waves at eastern ocean boundaries Part II: Pacific and Atlantic Oceans

Soares, Jacyra Ramos; Wainer, Ilana; Wells, N. C.

doi:10.1007/s00585-999-0827-5

Cited by 5 publications

(4 citation statements)

References 34 publications

(23 reference statements)

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“…The R k < 1 values in the CP and >1 values in the EP are also noticeable. Mechanisms controlling sea level variabilities of the central-eastern Pacific are different from those of the WTP (e.g., Bigg & Gill, 1986;Boutle et al, 2007;Qiu & Lukas, 1996;Soares et al, 1999), and therefore the asymmetric SLA responses there are out of the scope of the present study.…”

Section: S2mentioning

confidence: 95%

Asymmetry of Interannual Sea Level Variability in the Western Tropical Pacific: Responses to El Niño and La Niña

Ren

Zheng

et al. 2020

JGR Oceans

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The western tropical Pacific (WTP) exhibits pronounced large-scale sea level anomalies (SLAs) during El Niño-Southern Oscillation (ENSO) events with amplitudes of~0.1 m, exerting potential threats to many low-lying islands. It is found that the sea level falling in El Niño condition is evidently stronger than the rising in La Niña condition. This SLA asymmetry in the WTP associated with ENSO is investigated in this study, and the underlying dynamic processes are explored. Such asymmetry is most prominent at around 160°E with the SLA response to El Niño being three times stronger than to La Niña, but it is much inconspicuous near the western boundary. Sensitivity experiments of a simplified ocean model suggest that the different structures of surface wind anomalies between El Niño and La Niña conditions are critical in generating asymmetric SLA responses of the WTP. The El Niño's westerly wind anomaly patch locates more to the east than the La Niña's easterly wind patch during the mature stage, and its upwelling effects are accumulated over a wider longitude range and cause stronger negative SLAs in the WTP. Near the western boundary, however, upwelling effects are attenuated by easterly wind anomalies during the mature stage of El Niño. Further analysis reveals that eastern Pacific-type El Niño events are more favorable for generating asymmetric SLAs in the WTP than the central Pacific-type events. Plain Language Summary El Niño-Southern Oscillation (ENSO) is the most important climate variability phenomenon in the tropical Pacific and causes strong interannual sea level anomalies (SLAs) in the western tropical Pacific (WTP). The El Niño's sea level falling is evidently stronger than the La Niña's sea level rising. This difference is most prominent near 160°E with stronger El Niño's sea level falling but becomes much less evident near the western boundary of the Pacific Basin. The different surface wind anomaly structures between El Niño and La Niña are the primary cause. El Niño's westerly wind anomaly center locates more east than La Niña's easterly wind anomaly center in their mature phase, leading to stronger sea level falling in the WTP through westerly wind anomalies over the wide longitude range. The sea level falling is weakened by easterly wind anomalies generated near the western boundary. By contrast, effect of La Niña's easterly wind anomaly strengthens monotonically from east to west, and the produced sea level rising signatures are mainly confined to the WTP. The wind forcing structure of eastern Pacific-type El Niño is more favorable for generating asymmetric SLAs in the WTP than central Pacific-type events.

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Section: S2mentioning

confidence: 95%

Asymmetry of Interannual Sea Level Variability in the Western Tropical Pacific: Responses to El Niño and La Niña

Ren

Zheng

et al. 2020

JGR Oceans

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“…A similar decay is found in the linear model where it is due to viscous processes. Using a shallow water model, Soares et al (1999) found that a realistic shape of the coastline was more important than nonlinear effects for an accurate representation of the poleward energy flux at intraseasonal frequencies. In our fully three dimensional model (Fig.…”

Section: Horizontal Structure Of the Intraseasonal Signalmentioning

confidence: 99%

Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves

2009

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Abstract. In the Gulf of Guinea, intraseasonal variability is large at the equator and along the coast. Current data on the continental slope near 7.5 • S show very energetic biweekly oscillations at 1300 m depth. A high resolution primitive equation numerical model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastally-trapped waves upon reaching the coast of Africa. Intraseasonal variability is intensified along the coast of the Gulf of Guinea, especially in the 10-20 day period range and at depths between 500 and 1500 m. The kinetic energy distribution is well explained at first order by linear theory. Along the equator, eastward intensification of energy and bottom intensification are in qualitative agreement with vertically propagating Yanai waves, although the signal is influenced by the details of the bathymetry. Along the coast, baroclinic modes 3 to 5 are important close to the equator, and the signal is dominated by lower vertical modes farther south. Additional current meter data on the continental slope near 3 • N display an energy profile in the 10-20 day period band that is strikingly different from the one at 7.5 • S, with surface intensification rather than bottom intensification and a secondary maximum near 800 m. The model reproduces these features and explains them: the surface intensification in the north is due to the regional wind forcing, and the north-south asymmetry of the deep signal is due to the presence of the zonal African coast near 5 • N. A 4 years time series of current measurements at 7.5 • S shows that the biweekly oscillations are intermittent and vary from year to year. This intermittency is not well correlated with fluctuations of the equatorial winds and does not seem to be a simple linear response to the wind forcing.

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“…Note that the eastern boundary will also contribute a delay term to the DAO, however equatorial Kelvin wave reflection from eastern boundaries is weak as the bulk of the wave propagates along the coast [16]. For this reason we may ignore these effects.…”

Section: B Dao Wave Propagationmentioning

confidence: 99%

“…FIG.11: Numerical solutions to the coupled DAO(16), with α1 = 0.5 in region 1, α2 = 0.75 in region 2, δ = 4 in both regions and γ = 0.1.…”

mentioning

confidence: 99%

El Niño and the delayed action oscillator

Boutle¹,

Taylor²,

Röemer³

2007

American Journal of Physics

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We study the dynamics of the El Niño phenomenon using the mathematical model of delayedaction oscillator (DAO). Topics such as the influence of the annual cycle, global warming, stochastic influences due to weather conditions and even off-equatorial heat-sinks can all be discussed using only modest analytical and numerical resources. Thus the DAO allows for a pedagogical introduction to the science of El Niño and La Niña while at the same time avoiding the need for large-scale computing resources normally associated with much more sophisticated coupled atmosphere-ocean general circulation models. It is an approach which is ideally suited for student projects both at high school and undergraduate level.

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Reflection of equatorial Kelvin waves at eastern ocean boundaries Part II: Pacific and Atlantic Oceans

Cited by 5 publications

References 34 publications

Asymmetry of Interannual Sea Level Variability in the Western Tropical Pacific: Responses to El Niño and La Niña

Asymmetry of Interannual Sea Level Variability in the Western Tropical Pacific: Responses to El Niño and La Niña

Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves

El Niño and the delayed action oscillator

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