Regional atmospheric response to the Benguela Niñas

Koseki, Shunya; Koungue, Rodrigue Anicet Imbol

doi:10.1002/joc.6782

Cited by 13 publications

(11 citation statements)

References 54 publications

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“…The region exhibits high sea surface temperature (SST) variability at a wide range of frequencies varying from sub-monthly to decadal timescales (Bachèlery et al, 2020;Imbol Koungue and Brandt, 2021;Roch et al, 2021). The interannual timescale is marked by the occurrence of extreme warm events, the socalled Benguela Niños (Shannon et al, 1986;Florenchie et al, 2004;Rouault et al, 2007Rouault et al, , 2018Lübbecke et al, 2010;Bachèlery et al, 2016aBachèlery et al, , 2020Imbol Koungue et al, 2017 and their cold counterparts, the Benguela Niñas (Florenchie et al, 2004;Koseki and Imbol Koungue, 2020). Those interannual warm and cold events usually peak in boreal spring between March and April (Rouault et al, 2007;Lübbecke et al, 2010;Imbol Koungue et al, 2019) when the SSTs are climatologically high and the intertropical convergence zone (ITCZ) reaches its southernmost position.…”

Section: Introductionmentioning

confidence: 99%

“…Those extreme events may impact the marine ecosystem, biological productivity and fisheries in the Angola Benguela upwelling system by modulating the upward supply of nutrients (Bachèlery et al, 2016b) as they affect the upwelling intensity and upperocean mixing (Gammelsrød et al, 1998;Boyer et al, 2001;Blamey et al, 2015). Benguela Niños are often associated with floods in Angola and Namibia and strongly enhanced rainfall in the arid Namib desert (Rouault et al, 2003;Hansingo and Reason, 2009), whereas Benguela Niñas often lead to droughts over the Angola Benguela region (Koseki and Imbol Koungue, 2020).…”

Section: Introductionmentioning

confidence: 99%

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The 2019 Benguela Niño

et al. 2021

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High interannual sea surface temperature anomalies of more than 2°C were recorded along the coasts of Angola and Namibia between October 2019 and January 2020. This extreme coastal warm event that has been classified as a Benguela Niño, reached its peak amplitude in November 2019 in the Angola Benguela front region. In contrast to classical Benguela Niños, the 2019 Benguela Niño was generated by a combination of local and remote forcing. In September 2019, a local warming was triggered by positive anomalies of near coastal wind-stress curl leading to downwelling anomalies through Ekman dynamics off Southern Angola and by anomalously weak winds reducing the latent heat loss by the ocean south of 15°S. In addition, downwelling coastal trapped waves were observed along the African coast between mid-October 2019 and early January 2020. Those coastal trapped waves might have partly emanated from the equatorial Atlantic as westerly wind anomalies were observed in the central and eastern equatorial Atlantic between end of September to early December 2019. Additional forcing for the downwelling coastal trapped waves likely resulted from an observed weakening of the prevailing coastal southerly winds along the Angolan coast north of 15°S between October 2019 and mid-February 2020. During the peak of the event, latent heat flux damped the sea surface temperature anomalies mostly in the Angola Benguela front region. In the eastern equatorial Atlantic, relaxation of cross-equatorial southerly winds might have contributed to the equatorial warming in November 2019 during the peak of the 2019 Benguela Niño. Moreover, for the first time, moored velocities off Angola (11°S) revealed a coherent poleward flow in the upper 100 m in October and November 2019 suggesting a contribution of meridional heat advection to the near-surface warming during the early stages of the Benguela Niño. During the Benguela Niño, a reduction of net primary production in the Southern Angola and Angola Benguela front regions was observed.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The 2019 Benguela Niño

et al. 2021

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“…The main features of interannual SST variability over the ABA (8°E to the coast; 10-20°S, blue box in Figure 1a) are warm and cold events, the so-called Benguela Niños and Benguela Niñas (Shannon et al, 1986), respectively. Anomalous surface temperatures along the coasts of Angola and Namibia, typically lasting for a few months and peaking in MAM, impact the regional climate (Hansingo & Reason, 2009;Koseki & Imbol Koungue, 2020;Lutz et al, 2013;Rouault et al, 2003Rouault et al, , 2007 as well as marine ecosystems and fisheries (Bachèlery et al, 2016(Bachèlery et al, , 2019Binet et al, 2001;Gammelsrød et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Origin of Weakened Interannual Sea Surface Temperature Variability in the Southeastern Tropical Atlantic Ocean

Prigent

Koungue

Lübbecke

et al. 2020

Geophysical Research Letters

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Observations and reanalysis products are used to investigate the substantial weakening in the southeastern tropical Atlantic sea surface temperature (SST) variability since 2000. Relative to 1982-1999, the March-April-May SST variability in the Angola-Benguela area (ABA) has decreased by more than 30%. Both equatorial remote forcing and local forcing are known to play an important role in driving SST variability in the ABA. Compared to 1982-1999, since 2000, equatorial remote forcing had less influence on ABA SSTs, whereas local forcing has become more important. In particular, the robust correlation that existed between the equatorial zonal wind stress and the ABA SSTs has substantially weakened, suggesting less influence of Kelvin waves on ABA SSTs. Moreover, the strong correlation linking the South Atlantic Anticyclone and the ABA SSTs has reduced. Finally, multidecadal surface warming of the ABA could also have played a role in the weakening of the interannual SST variability. Plain Language Summary Every few years, the southeastern tropical Atlantic Ocean experiences anomalous sea temperatures that affect fisheries and rainfall. Using observations and reanalysis data, we quantify the Angola-Benguela area (ABA) sea surface temperature (SST) variability during the last decades. Relative to 1982-1999, the March-April-May SST variability in the ABA has decreased by more than 30% since 2000. Remote equatorial forcing through equatorially and coastally trapped oceanic waves and variations in the local winds are the main drivers of ABA SST variability. Since 2000, we find that ABA SSTs are less connected to equatorial winds and exhibit a weaker link with the South Atlantic Anticyclone. Finally, the surface warming of the ABA observed during the post-2000 period also could have played a role in the weakening interannual SST variability.

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“…On interannual time scales, many facets of the earth system shape Southern Africa precipitation. Chief among them are coupled atmosphere–ocean phenomena, which include ENSO (e.g., Nicholson & Entekhabi, 1986; Ropelewski & Halpert, 1987), the subtropical Indian Ocean Dipole (SIOD, e.g., Behera & Yamagata, 2001; Reason, 2001; Washington & Preston, 2006), the Indian Ocean Dipole (IOD, e.g., Gaughan et al, 2015; Williams & Hanan, 2011), and Benguela Niño and Niña (e.g., Hansingo & Reason, 2009; Koseki & Imbol Koungue, 2021; Nicholson & Entekhabi, 1987; Rouault et al, 2003). Regarding ENSO, its opposite phases, El Niño and La Niña, are on average related to opposite effects on the atmospheric circulation and precipitation in the region during its predominantly Austral summer wet season (e.g., Dieppois et al, 2016; Jury et al, 1994; Lindesay, 1988; Manatsa et al, 2011; Misra, 2003; Nicholson & Entekhabi, 1986; Nicholson & Kim, 1997; Reason et al, 2000; Rocha & Simmonds, 1997; Ropelewski & Halpert, 1987).…”

Section: Introductionmentioning

confidence: 99%

“…It is important to note that all ENSO events are different (e.g., Capotondi et al, 2015; Wyrtki, 1975), and differences in terms of their SST patterns and magnitude have been found to affect Southern Africa precipitation differently (e.g., Gore et al, 2020; Hoell et al, 2015; Pomposi et al, 2018; Ratnam et al, 2014). Regarding Benguela Niño and Niña, which are defined by SST anomalies along the coast of Namibia (e.g., Rouault & Tomety, 2022; Shannon et al, 1986), they are related to precipitation in far western areas of Southern Africa, including Namibia and Angola (e.g., Hansingo & Reason, 2009; Koseki & Imbol Koungue, 2021; Nicholson & Entekhabi, 1987; Rouault et al, 2003).…”

Section: Introductionmentioning

confidence: 99%