Propagation and origin of warm anomalies in the Angola Benguela upwelling system in 2001

Rouault, Mathieu; Illig, Séréna; Bartholomae, C.; Reason, C. J. C.; Bentamy, Abderrahim

doi:10.1016/j.jmarsys.2006.11.010

Cited by 98 publications

(141 citation statements)

References 48 publications

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“…The variability of the Angola Current appears to be largely controlled by the passage of coastally trapped waves (CTWs; Ostrowski et al 2009;Rouault 2012;Bachèlery et al 2016;Kopte et al 2017). These waves communicate equatorial oceanic variability along the continental margin of Angola to the northern Benguela upwelling region.…”

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

“…In addition, altimetry and regional ocean simulations revealed equatorial forced CTWs having interannual time scales (13-20 months; Bachèlery et al 2016). Along the Angolan and Namibian continental margin, CTWs contribute to triggering sea surface temperature (SST) anomalies, which impact atmospheric circulation and rainfall (Shannon et al 1986;Rouault et al 2003;Imbol Koungue et al 2017;Rouault et al 2018). CTWs may also modulate biogeochemical conditions in the coastal upwelling ecosystems and directly impact fisheries by displacing fish eggs and larvae latitudinally along the continental margin (e.g., Ostrowski 2007).…”

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

“…The front fluctuates in position and strength on time scales from intraseasonal (Kostianoy and Lutjeharms 1999;Mohrholz et al 2001;Goubanova et al 2013;Diakhaté et al 2016) to annual (Meeuwis and Lutjeharms 1990) to interannual. Interannual variability in the frontal region is often associated with severe warm and cold events during austral summer termed Benguela Niños and Benguela Niñas, respectively (Shannon et al 1986;Florenchie et al 2004;Rouault et al 2018). Benguela Niños are marked by a poleward intrusion of warm equatorial water and reduced upwelling (Fig.…”

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

“…The ocean currents at the continental margin represent a typical tropical eastern boundary circulation system dominated by the poleward-f lowing Angola Current. Predominately during austral summer, the Angola Current is thought to tra nspor t warm a nd saline, low-oxygen South At la ntic Centra l Water (SACW) southward into the coastal upwelling region, possibly resulting in hypoxic to anoxic conditions on the shelf (Mohrholz et al 2008;Monteiro et al 2008;Rouault 2012). In turn, the Angola Current is thought to be supplied by the eastward currents in the equatorial region (Peterson and Stramma 1991;Wacongne and Piton 1992;Rouault et al 2007).…”

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confidence: 99%

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Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

Tchipalanga

Dengler

Brandt

et al. 2018

Bulletin of the American Meteorological Society

122

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The eastern boundary region off Angola encompasses a highly productive ecosystem important for the food security of the coastal population. The fish-stock distribution, however, undergoes large variability on intraseasonal, interannual, and longer time scales. These fluctuations are partly associated with large-scale warm anomalies that are often forced remotely from the equatorial Atlantic and propagate southward, reaching the Benguela upwelling off Namibia. Such warm events, named Benguela Niños, occurred in 1995 and in 2011. Here we present results from an underexplored extensive in situ dataset that was analyzed in the framework of a capacity-strengthening effort. The dataset was acquired within the Nansen Programme executed by the Food and Agriculture Organization of the United Nations and funded by the Norwegian government. It consists of hydrographic and velocity data from the Angolan continental margin acquired biannually during the main downwelling and upwelling seasons over more than 20 years. The mean seasonal changes of the Angola Current from 6° to 17°S are presented. During austral summer the southward Angola Current is concentrated in the upper 150 m. It strengthens from north to south, reaching a velocity maximum just north of the Angola Benguela Front. During austral winter the Angola Current is weaker, but deeper reaching. While the southward strengthening of the Angola Current can be related to the wind forcing, its seasonal variability is most likely explained by coastally trapped waves. On interannual time scales, the hydrographic data reveal remarkable variability in subsurface upper-ocean heat content. In particular, the 2011 Benguela Niño was preceded by a strong subsurface warming of about 2 years’ duration.

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Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

Tchipalanga

Dengler

Brandt

et al. 2018

Bulletin of the American Meteorological Society

122

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“…This intensification might be related to the northerly wind biases along the African coast, which peaks about 2-3 months before the maximum SST bias. Many studies have also suggested that wind stress along the equator exerts a crucial influence on the coastal region of southwestern Africa via Kelvin waves for both interannual (Florenchie et al 2004, Rouault et al 2007, Lubbecke et al 2010) and seasonal variability (Moore et al 1978;Yamagata and Iizuka 1996).…”

Section: Southeast Atlantic Biasesmentioning

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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Seasonal variability of alongshore winds and sea surface temperature fronts in Eastern Boundary Current Systems

2015

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Seven years of satellite observations (2003)(2004)(2005)(2006)(2007)(2008)(2009)) are used to describe variability in sea surface temperature (SST) fronts and in the alongshore component of ocean winds, and to investigate their relations in four Eastern Boundary Current Systems (EBCS). The general patterns of SST frontal activity are remarkably similar in all EBCS, with high frontal probabilities along the coast decreasing with distance from the coastline. Results from empirical orthogonal function decompositions reveal that the seasonal evolution of SST fronts and wind stress are significantly correlated, with intensified upwelling favorable winds associated with an increase in frontal probabilities. An offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in EBCS. In all regions, the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes. The width of the region of high frontal activity is relatively broader in the California and Benguela Current Systems, and narrower in the Canary and Humboldt Current Systems. The width of the band of high frontal activity may be influenced by multiple factors, including wind forcing, flow topography interactions, and mesoscale dynamics. While seasonal variability in frontal activity in the California Current System acts to reinforce or weaken the average pattern, they are substantially different in the Canary Current System, where there is little overlap in the areas characterized by persistent and seasonally varying front activity.

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Propagation and origin of warm anomalies in the Angola Benguela upwelling system in 2001

Cited by 98 publications

References 48 publications

Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

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

Seasonal variability of alongshore winds and sea surface temperature fronts in Eastern Boundary Current Systems

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