greta leber rosenstiel school of marine and atmospheric science student seminar presentation:...
TRANSCRIPT
![Page 1: Greta Leber Rosenstiel School of Marine and Atmospheric Science Student Seminar Presentation: December 1, 2010 Advisor: Dr. Lisa Beal](https://reader033.vdocuments.mx/reader033/viewer/2022051618/56649f585503460f94c7d33e/html5/thumbnails/1.jpg)
HYDROGRAPHIC SURVEY OF A SOLITARY
MEANDER IN THE AGULHAS CURRENT
Greta Leber
Rosenstiel School of Marine and Atmospheric Science
Student Seminar Presentation: December 1, 2010
Advisor: Dr. Lisa Beal
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BACKGROUND: The Agulhas System
Image Courtesy Dr. Lisa Beal
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BACKGROUND: Description of the ACT Project
Average Vertical Spacing: 2mAverage Horizontal Spacing: 23km
Lowered Acoustic Doppler Current Profiler (LADCP) with Conductivity-
Temperature-Depth (CTD)
Line 1: LADCP + CTD During Deployment: Less
Synoptic: April 7-15
Steamed back for a continuous underway
shipboard ADCP section
Line 2: LADCP + CTD More Synoptic: April 17-
19
Image Courtesy Dr. Lisa Beal
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BACKGROUND: Non-meander Phase
Images Courtesy Dr. Lisa Beal
Agulhas Undercurrent Experiment East London line
February-March 2003
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BACKGROUND: Solitary Meander Phase
Solitary Meander Characteristics (de Ruijter et al, 1999):
• Downstream velocity ranges from 5 (North) to 20 (South) km day-1, • Diameter ranges from 30-200 km•Period between 50 and 150 days.
Marine Remote Sensing Unit; http://www.afro-sea.org.za/mrsu/flags.php
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BACKGROUND: Solitary Meander during ACT
April 7
April 12
April 15
April 17
April 18
April 19
Line 2
Line 1
Diameter: ~100km Velocity: ~15 km day-1 downstream
SSALTO/ Data Unification and Altimeter Combination System (DUACS) Real-Time AVISO MADT Product
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ANALYSIS: Direct Velocities (LADCP)Line 1 Line 2
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ANALYSIS: Cumulative Transport Across Lines
Line 1 Line 2
Northeastward (Undercurrent) 68.3 19.2
Southwestward (Agulhas) 128.2 129.1
Total (Southwestward) 59.9 109.8
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ANALYSIS: Calculating Geostrophic FlowNeed a ZVS… commonly:But, we know that the ZVS is V-shaped, so use ZVS from LADCP data:
Still no Northeastward
(Barotropic Feature)!
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ANALYSIS: Calculating Geostrophic Flow SOLUTION:
Demean the Geostrophic Velocity and add Geostrophic Barotropic component from LADCP.
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ANALYSIS: Ageostrophic FlowLine 1 Line 2
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SUMMARY AND FUTURE WORK
During the passage of a Solitary Meander, the northward flow strengthens and extends to the surface as a barotropic feature.
Geostrophic velocity is highly sensitive to the choice of a ZVS, with comparison to LADCP barotropic component giving the best results.
Ageostrophic flows in the Agulhas are concentrated in the surface layer.
Next Steps (with the hydrographic data): Investigate structure of ageostrophic flow (Cylostrophic?
Ekman? Data artifact?). Continue evaluating meander properties (vorticity, mixing,
etc.).
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ACKNOWLEDGEMENTS
My advisor, Dr. Lisa Beal. The crew of the R.V. Knorr Funded by NSF
THANK YOU!
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BACKGROUND: Description of the ACT Project
Images Courtesy Dr. Lisa Beal
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MOTIVATION: Why Study the Agulhas?
Largest WBC in the world (Bryden and Beal,
2005) Large heat and salt transports.
Important inter-ocean link in the Thermohaline Circulation as the so-called ‘warm-water
route’ first described by Gordon, 1986. Upstream dynamics have
been linked to frequency of ring-shedding events (Lutjeharms and van Ballegooyen, 1988; van Leeuwen et al, 2000).
Zahn, 2009
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SSALTO/ Data Unification and Altimeter Combination System (DUACS) Real-Time AVISO MADT Product