The source of Benguela Niños in the South Atlantic Ocean

Florenchie, P.; Lütjeharms, J. R. E.; Reason, C. J. C.; Masson, Sébastien; Rouault, Mathieu

doi:10.1029/2003gl017172

Cited by 133 publications

(115 citation statements)

References 12 publications

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“…Additionally, shown in Fig. 3 are corresponding anomalies in the simulated depth of the 238C isotherm (z23), which is a measure of the thermocline depth (Florenchie et al 2003). The thermocline depth and SSH anomalies from the model simulation agree well with correlations of 0.84 and 0.63, respectively, as a consequence of the fact that the tropical Atlantic behaves much like a two-layer system.…”

Section: Model Validationsupporting

confidence: 65%

On the Inconsistent Relationship between Pacific and Atlantic Niños*

Lübbecke

McPhaden

2012

Journal of Climate

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The tropical Atlantic wind response to El Niñ o forcing is robust, with weakened northeast trade winds north of the equator and strengthened southeast trade winds along and south of the equator. However, the relationship between sea surface temperature (SST) anomalies in the eastern equatorial Pacific and Atlantic is inconsistent, with El Niñ o events followed sometimes by warm and other times by cold boreal summer anomalies in the Atlantic cold tongue region. Using observational data and a hindcast simulation of the Nucleus for European Modeling of the Ocean (NEMO) global model at 0.58 resolution (NEMO-ORCA05), this inconsistent SST relationship is shown to be at least partly attributable to a delayed negative feedback in the tropical Atlantic that is active in years with a warm or neutral response in the eastern equatorial Atlantic. In these years, the boreal spring warming in the northern tropical Atlantic that is a typical response to El Niñ o is pronounced, setting up a strong meridional SST gradient. This leads to a negative wind stress curl anomaly to the north of the equator that generates downwelling Rossby waves. When these waves reach the western boundary, they are reflected into downwelling equatorial Kelvin waves that reach the cold tongue region in late boreal summer to counteract the initial cooling that is due to the boreal winter wind stress response to El Niñ o. In contrast, this initial cooling persists or is amplified in years in which the boreal spring northern tropical Atlantic warming is weak or absent either because of a positive North Atlantic Oscillation (NAO) phase or an early termination of the Pacific El Niñ o event.

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Section: Model Validationsupporting

confidence: 65%

On the Inconsistent Relationship between Pacific and Atlantic Niños*

Lübbecke

McPhaden

2012

Journal of Climate

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“…12). The SST anomalies along the coast of Angola and Namibia are associated with Benguela Niño, which is closely related to precipitation anomalies in the western part of southern Africa (Rouault et al 2003;Florenchie et al 2003). Since it is predicted relatively well in the 1990s, it may partly explain the better prediction skills in this decade when the correlation between ENSO and the southern African summer precipitation is relatively weak (Fig.…”

Section: Large-scale Circulation Anomalies Related To the Above/belowmentioning

confidence: 99%

Dynamical seasonal prediction of Southern African summer precipitation

et al. 2013

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Prediction skills for southern African (16˚-33˚E, 22˚-35˚S) summer precipitation in the Scale Interaction Experiment-Frontier coupled model is assessed for the period of 1982-2008. Using three different observation datasets, deterministic forecasts are evaluated by anomaly correlation coefficients, whereas scores of relative operating characteristic and relative operating level are used to evaluate probabilistic forecasts. It is shown that these scores for forecasts of December-February precipitation initialized on October 1 st are significant at 95%confidence level. On a local scale, the prediction skills in the northwestern and central parts of southern Africa are higher than those in northeastern South Africa. El Niño/Southern Oscillation (ENSO) provides the major source of predictability, but the relationship with ENSO is over-confident in the model. Also, the Benguela Niño, the basin mode in the tropical Indian Ocean, the subtropical dipole modes in the South Atlantic and the southern IndianOceans and ENSO Modoki may provide additional sources of predictability. When prediction skills are evaluated for the whole wet season from October to the following April, it is found that precipitation anomalies in December-February are most predictable. The present study presents promising results for seasonal prediction of precipitation anomalies in the extratropics, where seasonal forecast are considered a difficult task.3

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“…This is indicative of coastal thermocline adjustments in response to the altered MAM equatorial wind stress. Such remote influences from the equator are believed to play a role in the development of interannual warm events in the Angola/Benguela region (also named Benguela Niños) and several studies suggest that this influence is mediated via Kelvin waves (Florenchie et al 2003;Polo et al 2008, Lubbecke et al 2010). This Kelvin wave mechanism might also be at work in the sensitivity experiment.…”

Section: The Influence Of Mam Wind Stressmentioning

confidence: 99%

Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation

et al. 2011

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Most coupled general circulation models (GCMs) perform poorly in the tropical Atlantic in terms of climatological seasonal cycle and interannual variability. The reasons for this poor performance are investigated in a suite of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory (GFDL) coupled GCM. The experiments show that a significant portion of the equatorial SST biases in the model is due to weaker than observed equatorial easterlies during boreal spring. Due to these weak easterlies, the tilt of the equatorial thermocline is reduced, with shoaling in the west and deepening in the east. The erroneously deep thermocline in the east prevents cold tongue formation in the following season despite vigorous upwelling. The Bjerknes feedback further amplifies the SST biases and prolongs their effect in boreal summer when equatorial winds are close to observations. It is further shown that the surface wind errors are due, in part, to deficient precipitation over equatorial South America and excessive precipitation over equatorial Africa, which already exist in the uncoupled atmospheric GCM. Additional tests indicate that the precipitation biases are highly sensitive to land surface conditions such as albedo and soil moisture. This suggests that improving the representation of land surface processes in GCMs offers a way of improving their performance in the tropical Atlantic.The weaker than observed equatorial easterlies also contribute remotely, via equatorial and coastal Kelvin waves, to the severe warm SST biases along the southwest African coast. However, the strength of the subtropical anticyclone and along-shore winds also play an important role.3

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The source of Benguela Niños in the South Atlantic Ocean

Cited by 133 publications

References 12 publications

On the Inconsistent Relationship between Pacific and Atlantic Niños*

On the Inconsistent Relationship between Pacific and Atlantic Niños*

Dynamical seasonal prediction of Southern African summer precipitation

Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation

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