Contents

Agulhas Current Variability:

A challenge across industry sectors

Marjolaine Krug

Ecosystem Earth Observations (CSIR-NRE)

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• Intense ship traffic

• Strong currents

• Intense and frequent of storms

• Intense Wave / Current interactions

which results in crossing seas and

rogue waves (up to half of ship

accidents due to bad weather occur

in crossing seas)

Image provided in Ocean-Volvo race

Damage caused by rogue wave and Ship wrecks

location

Ship traffic from AIS on 10 Jan 2016 (image

by Rory Meyer - Meraka)

Background

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Background

• Strongest western boundary current of the southern hemisphere and maybe of the

world (Bryden 2005)

• Driven by the anticyclonic wind circulation of the South-Indian subtropical gyre

• Starts around Ponto de Ouro (27oS, Mozambique) - Ends at the retroflection (40oS)

• Variability in the Mozambique Channel and south of Madagascar transmitted into

the northern Agulhas Current in the form of deep sea eddies, which can lead to the

formation of large cyclonic Agulhas Current meanders

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Mesoscale variability

Trajectories of surface drifters

reaching the Natal Bight

between 1992 and 2002

(Braby et al., 2016)

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Mesoscale variability

Sea surface temperature and

currents derived from sea

surface height show presence of

large Agulhas meander

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EO monitoring

Deriving index of variability from altimetry (method in Krug et al., 2014).

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EO monitoring

Year 2000

The year of the great Agulhas

Current Early Retroflection

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EO monitoring

Altimetry challenged by lack of

temporal and spatial coverage

when monitoring smaller

scales and / or rapidly evolving

structures.

Potential to exploit other

remote sensing products such

as SST for EO monitoring.

(Rouault and Penven 2011)

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EO monitoring

Daily changes in the position

of the Agulhas Current

northern wall derived from

merged Odyssea SST.

(Krug et al., submitted)

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Sub-mesoscale variability

Sub-mesoscale

variability at the Agulhas

Current northern wall.

Observations collected

during the Shelf Agulhas

Glider Experiment

(SAGE).

(Krug et al., submitted)

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Sub-mesoscale variability

Max ζ/f = 1.02

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Future plans

Exploiting new EO datasets

Increasing our in-situ observations

Improving our models