Multidecadal Wind Variability Drives Temperature Shifts on the Agulhas Bank

Malan, Neil; Durgadoo, Jonathan V.; Biastoch, Arne; Reason, C. J. C.; Hermes, Juliet

doi:10.1029/2018jc014614

Cited by 14 publications

(9 citation statements)

References 44 publications

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“…Similar trends in local air-sea interactions are attributed to more frequent wind-driven coastal upwelling and easterly winds (see Fig. 3a) as in Malan et al (2019). Coupled ensemble projections from the Hadley and European models indicate that the shift toward drier weather, easterly winds, coastal upwelling, and a locally faster Agulhas Current may be sustained through the 21st century (see Fig.…”

Section: Discussion and Summarysupporting

confidence: 62%

“…4a-d) for 18-month filtered SST, zonal winds, currents, vertical motion, and rainfall. There is a multiyear alternation of warm and cool spells, modulated by local winds, the Pacific El Niño-La Niña (Jury, 2015(Jury, , 2019, and the Southern Annular Mode (Malan et al, 2019). There is a background trend of inshore cooling and offshore warming that intensifies the coastal gradient (Fig.…”

Section: Shelf Analysis and Gradientsmentioning

confidence: 99%

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Marine climate change over the eastern Agulhas Bank of South Africa

Jury

2020

Ocean Sci.

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Abstract. The rate of change in the marine environment over the eastern Agulhas Bank along the south coast of South Africa (32–37∘ S, 20–30∘ E) is studied using reanalysis observations for 1900–2015 and coupled ensemble model projections for 1980–2100. Outcomes are influenced by resolution and time span: ∼ 1∘ datasets covering the whole period capture large-scale changes, while ∼ 0.5∘ datasets in the satellite era better distinguish the cross-shelf gradients. Although sea surface temperatures offshore are warming rapidly (0.05 ∘C yr−1 since 1980), a trend toward easterly winds and a locally stronger Agulhas Current have intensified nearshore upwelling (−0.03 ∘C yr−1). The subtropical ridge is gradually moving poleward, leading to a drier climate.

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Section: Discussion and Summarysupporting

confidence: 62%

Section: Shelf Analysis and Gradientsmentioning

confidence: 99%

Marine climate change over the eastern Agulhas Bank of South Africa

Jury

2020

Ocean Sci.

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“…Consequently, the stronger AABW cell slightly lifts and, more importantly, dampens the upper overturning cell as suggested by Frajka-Williams et al (2011) from hydrographic observations at 24.5 • N as well as from modelling studies (e.g. Swingedouw et al, 2009;Martin et al, 2015).…”

Section: Atlantic Meridional Overturning Circulationmentioning

confidence: 65%

The INALT family – a set of high-resolution nests for the Agulhas Current system within global NEMO ocean/sea-ice configurations

et al. 2019

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Abstract. The Agulhas Current, the western boundary current of the South Indian Ocean, has been shown to play an important role in the connectivity between the Indian and Atlantic oceans. The greater Agulhas Current system is highly dominated by mesoscale dynamics. To investigate their influence on the regional and global circulations, a family of high-resolution ocean general circulation model configurations based on the NEMO code has been developed. Horizontal resolution refinement is achieved by embedding “nests” covering the South Atlantic and the western Indian oceans at 1/10∘ (INALT10) and 1/20∘ (INALT20) within global hosts with coarser resolutions. Nests and hosts are connected through two-way interaction, allowing the nests not only to receive boundary conditions from their respective host but also to feed back the impact of regional dynamics onto the global ocean. A double-nested configuration at 1/60∘ resolution (INALT60) has been developed to gain insights into submesoscale processes within the Agulhas Current system. Large-scale measures such as the Drake Passage transport and the strength of the Atlantic meridional overturning circulation are rather robust among the different configurations, indicating the important role of the hosts in providing a consistent embedment of the regionally refined grids into the global circulation. The dynamics of the Agulhas Current system strongly depend on the representation of mesoscale processes. Both the southward-flowing Agulhas Current and the northward-flowing Agulhas Undercurrent increase in strength with increasing resolution towards more realistic values, which suggests the importance of improving mesoscale dynamics as well as bathymetric slopes along this narrow western boundary current regime. The exploration of numerical choices such as lateral boundary conditions and details of the implementation of surface wind stress forcing demonstrates the range of solutions within any given configuration.

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“…Cooler near-shore sea temperatures contribute to atmospheric subsidence, drying trends (-.005 mm day -1 /yr) and vegetation warming (.1°C/yr). Similar trends in local air-sea interactions are attributed to more frequent wind-driven coastal upwelling in Malan et al (2019). Coupled ensemble projections from the Hadley and European models indicate that the shift toward drier weather, easterly winds, coastal upwelling and a faster Agulhas Current may be sustained through the 21 st century.…”

Section: Discussion and Summarymentioning

confidence: 62%

“…Hovmoller plots were constructed across the southern shelf (Fig 4a,b) for 18-month filtered surface temperature and zonal currents. Warm spells during westerly wind-driven downwelling contrast with cool spells during easterly wind-driven upwelling: a multi-year alternation modulated by Pacific El Nino / La Nina (Jury 2015 and the Southern Annular Mode (Malan et al 2019). Yet there is a background trend toward inshore cooling and offshore warming that intensifies the coastal gradient.…”

Section: Shelf Analysis and Gradientsmentioning

confidence: 99%

Marine climate change over the eastern Agulhas Bank of South Africa

Jury¹

2020

Preprint

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Abstract. The rate of change in the marine environment along the south coast of South Africa (32–37 S, 20–30 E) is studied using reanalysis observations 1900–2015 and coupled ensemble model projections 1980–2100. Outcomes are influenced by resolution and time-span: ~1 degree datasets covering the whole period capture large-scale changes, while ~0.5 degree datasets in the satellite era better distinguish the cross-shelf gradients. Although sea surface temperatures off-shore are warming rapidly (.05 °C/yr since 1980), a trend toward easterly winds and a stronger Agulhas Current have intensified near-shore upwelling (-.03 °C/yr). The sub-tropical ridge during summer is drawn poleward by global warming and high phase southern oscillation index. Cooler inshore sea temperatures suppress latent heat flux and contribute to coastal desiccation (-.005 mm day−1/yr) and vegetation warming (.1 °C/yr) since 1980. Coupled ensemble projections from the Hadley and European models indicate that the shift toward drier weather and easterly winds may be sustained through the 21st century.

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Multidecadal Wind Variability Drives Temperature Shifts on the Agulhas Bank

Cited by 14 publications

References 44 publications

Marine climate change over the eastern Agulhas Bank of South Africa

Marine climate change over the eastern Agulhas Bank of South Africa

The INALT family – a set of high-resolution nests for the Agulhas Current system within global NEMO ocean/sea-ice configurations

Marine climate change over the eastern Agulhas Bank of South Africa

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