Three‐Dimensional Numerical Simulations of Internal Tides in the Angolan Upwelling Region

Zhi, Zeng; Brandt, Peter; Lamb, Kevin G.; Greatbatch, Richard John; Dengler, Marcus; Claus, Martin; Chen, Xueen

doi:10.1029/2020jc016460

Cited by 19 publications

(36 citation statements)

References 55 publications

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“…Other factors such as the strength of stratification and mixing might play a role as well. A recent modeling study showed that the tidal energy available for mixing at the Angolan shelf is similar throughout the year, albeit the resulting mixing is more efficient during periods of shallow thermocline (Zeng et al, 2021…”

Section: Discussionmentioning

confidence: 99%

“…It strengthens the seasonal downwelling in February and October and weakens the upwelling in June/July. The main upwelling season of Angola is in July-September (Kopte et al, 2017;Ostrowski et al, 2009;Zeng et al, 2021). This upwelling signal is again strengthened in its later phase by the upwelling wave of the phase-locked 120-day oscillations peaking in August/September.…”

Section: Impacts On the Sst Variabilitymentioning

confidence: 96%

“…The identified 120-day oscillations contribute to the seasonal cycle of upwelling and downwelling waves along the Angolan coast. Seasonal variations of the SLA are dominated by a semiannual cycle with downwelling waves occurring in February/March and October/November; the SLA amplitude of the semiannual cycle is about 5 cm (Rouault, 2012;Zeng et al, 2021, their Figure 1c). The amplitude of the intraseasonal variability might reach more than 3 cm and substantially contribute to SLA variations during some years.…”

Section: Impacts On the Sst Variabilitymentioning

confidence: 99%

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Impact of Intraseasonal Waves on Angolan Warm and Cold Events

Koungue

Brandt

2021

JGR Oceans

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The Angolan upwelling system as part of the tropical eastern boundary upwelling system, is a highly productive ecosystem (Binet et al., 2001;Jarre et al., 2015). The warm Angola Current connects the equatorial Atlantic with the Angolan and Benguela upwelling systems by transporting warm tropical waters southward (Rouault, 2012;Tchipalanga et al., 2018) which can be linked to coastal extreme warm events the so-called

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Section: Discussionmentioning

confidence: 99%

Section: Impacts On the Sst Variabilitymentioning

confidence: 96%

Section: Impacts On the Sst Variabilitymentioning

confidence: 99%

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Impact of Intraseasonal Waves on Angolan Warm and Cold Events

Koungue

Brandt

2021

JGR Oceans

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“…Meteorologically, the SETA region is situated on the northeastern flank of the South Atlantic Subtropical High (SASH) and therefore, the wind pattern is influenced by the southeast trades (Peterson and Stramma, 1991). In the northern part of the SETA region the mainly southerly wind is considerably weak (Risien et al, 2004;Fennel et al, 2012;Lübbecke et al, 2019;Zeng et al, 2021). Besides, in austral winter when SSTs are lowest, the upwelling favorable winds are weakest and thus, the shallowing of the thermocline occurring during that part of the year is not wind-driven.…”

Section: Introductionmentioning

confidence: 99%

“…Instead, enhanced biological productivity off Angola in austral winter is mainly associated with the propagation of an upwelling CTW (e.g., Ostrowski et al, 2009;Rouault, 2012;Lübbecke et al, 2019). Mixing dominantly induced by internal tides (Zeng et al, 2021) transfers the CTW upwelling signal toward the surface to further modulate near coastal SST (Imbol Koungue and Brandt, 2021) and transport nutrients upward into the euphotic zone.…”

Section: Introductionmentioning

confidence: 99%

Southeastern Tropical Atlantic Changing From Subtropical to Tropical Conditions

et al. 2021

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A warming and freshening trend of the mixed layer in the upper southeastern tropical Atlantic Ocean (SETA) is observed by the Argo float array during the time period of 2006–2020. The associated ocean surface density reduction impacts upper-ocean stratification that intensified by more than 30% in the SETA region since 2006. The initial typical subtropical stratification with a surface salinity maximum is shifting to more tropical conditions characterized by warmer and fresher surface waters and a subsurface salinity maximum. During the same period isopycnal surfaces in the upper 200 m are shoaling continuously. Observed wind stress changes reveal that open ocean wind curl-driven upwelling increased, however, partly counteracted by reduced coastal upwelling due to weakened alongshore southerly winds. Weakening southerly winds might be a reason why tropical surface waters spread more southward reaching further into the SETA region. The mixed layer warming and freshening and associated stratification changes might impact the marine ecosystem and pelagic fisheries in the Angolan and northern Namibian upwelling region.

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Physical Drivers of Southwest African Coastal Upwelling and Its Response to Climate Variability and Change

Brandt,

Bordbar,

Coelho

et al. 2024

Ecological Studies

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The southeastern tropical Atlantic hosts a coastal upwelling system characterized by high biological productivity. Three subregions can be distinguished based on differences in the physical climate: the tropical Angolan and the northern and southern Benguela upwelling systems (tAUS, nBUS, sBUS). The tAUS, which is remotely forced via equatorial and coastal trapped waves, can be characterized as a mixing-driven system, where the wind forcing plays only a secondary role. The nBUS and sBUS are both forced by alongshore winds and offshore cyclonic wind stress curl. While the nBUS is a permanent upwelling system, the sBUS is impacted by the seasonal cycle of alongshore winds. Interannual variability in the region is dominated by Benguela Niños and Niñas that are warm and cold events observed every few years in the tAUS and nBUS. Decadal and multidecadal variations are reported for sea surface temperature and salinity, stratification and subsurface oxygen. Future climate warming is likely associated with a southward shift of the South Atlantic wind system. While the mixing-driven tAUS will most likely be affected by warming and increasing stratification, the nBUS and sBUS will be mostly affected by wind changes with increasing winds in the sBUS and weakening winds in the northern nBUS.

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Three‐Dimensional Numerical Simulations of Internal Tides in the Angolan Upwelling Region

Abstract: Tropical eastern boundary upwelling systems are characterized by rich marine ecosystems (Carr & Kearns, 2003). They undergo strong intraseasonal to interannual variability dominantly associated with equatorial forcing and are often subject to intense hypoxia (e.g.,

Cited by 19 publications

References 55 publications

Impact of Intraseasonal Waves on Angolan Warm and Cold Events

Impact of Intraseasonal Waves on Angolan Warm and Cold Events

Southeastern Tropical Atlantic Changing From Subtropical to Tropical Conditions

Physical Drivers of Southwest African Coastal Upwelling and Its Response to Climate Variability and Change

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