Warm-core Agulhas Plateau Eddies

Warm-core Agulhas Plateau Eddies
Jeffrey W. Book1,, Ana E. Rice2, Warren T. Wood1 , Charlie Barron1,
Isabelle Ansorge3, and Raymond Roman3
1Naval
Research Laboratory, U.S.A.
2NRC Postdoctoral Research Associate, Naval Research Laboratory, U.S.A
3University of Cape Town, Cape Town , South Africa
Past Descriptions of Warm-core Agulhas Plateau Eddies
Lutjeharms and Valentine, 1988, Journal of Physical Oceanography
Standard deviation of 3 years of daily sea-surface steric height anomalies from
MODAS-2D absolute sea-surface steric height anomalies. The location of the 1.5 m
SSH isoline is also indicated (Boebel et al., 2003, Deep Sea Research II)
Update of Boebel et al. 2003 results
Standard deviation of 16 years of daily sea-surface
steric height anomalies from MODAS-2D absolute seasurface steric height anomalies.
MODAS movie Nov. 2010 – Mar. 2012
MODAS SSH map for beginning of ARC12 cruise
Agulhas Return Current / Eddy Collision
ARC12 Cruise: January 23 - February 8, 2012
CTD
Microstructure
Seismic & XBT
UCTD
Agulhas Plateau Eddy Structure
Eddy radial crossing survey performed on Feb. 2-3, 2012
• Radius of more than 120 km
• Upper 800 m transport exceeding 57 Sv
• Maximum velocity exceeding 1.4 m/s
• Core velocities centered at 60 km radius
• 90-100 km wide down to a depth of 350 m
• 50 km wide to a depth of 600 m.
Seismic Oceanography: how it works
hydrophone array
Sound source
(0.1oC/m)
T contrast
T contrast
Holbrook et al. (Science, 2003)
popularized and advanced the concept
of using marine seismic reflection
profiling to image oceanic thermohaline
structure.
Seismic reflections occur off impedance
contrasts in the water column and due
to typical thermal control of c, provide a
measure of dT/dz.
Seismic Measurement as a Convolution Sum
seismic
measurement
seismic
wavelet
water-column
profile of reflectivity
The seismic wavelet causes dT/dz peaks to extend downward in the resulting seismic
image by 20 m or more creating multiple peaks and troughs all associated with the
same thermal structure
Seismic Image of Agulhas Plateau Eddy
Seismic Image and Velocity of Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Anatomy of an Agulhas Plateau Eddy
Temperature/Salinity Structure of an Agulhas Plateau Eddy
Temperature/Salinity Structure of an Agulhas Plateau Eddy
Temperature/Salinity Structure of an Agulhas Plateau Eddy
Some Possible Questions for Discussion
These new observations provide a basis to begin to re-examine the role of such large
warm-core anticyclones inside the Agulhas Current System.
1. What role do they play in mixing of subtropical and subantarctic waters?
2. Do they have a recurrent role in the shedding of rings to the Atlantic through
indirect interactions with currents to the west of the Plateau?
3. How important is it for models to resolve these eddies and properly account for
their interactions with the main current?
THANKS!
In Memory