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Agulhas Leakage depends on the Westerlies
Jonathan Durgadoo
Arne Biastoch
ICSHMO 2012
New Caledonia
23 Apr 2012
Summarised version of presentation More details: [email protected]
Agulhas Current System: An Apercu.
Agulhas Current
What does the Leakage depend on?
Strong year-to-year variability!
How does the magnitude of the Leakage vary?
Sources of Agulhas Current
Leakage Dependency
Agulhas Current Winds Patterns
Inertia at Separation
Zero-Curl Position
How does the wind field affect the Agulhas leakage?
INALT01
• Global (0.5 deg. horizontal resolution) • 45 km resolution over Agulhas domain.
• Global Base = ORCA05. • Coupled Nest (0.1 deg. horizontal resolution) • 8oN – 50oS; 70oW – 70oE. • 9 km resolution over Agulhas domain.
ORCA05 does not resolve mesoscale.
resolves the mesoscale. Grid Size (km)
• z-coordinate (46 levels), partial cells
• Tri-polar horizontal grid
– Mercator south of 20oN
• LIM2 sea-ice model
• ETOPO2 bathymetry (Nest)
Grid Size (km)
Experiment Strategy. How do the wind patterns affect the Agulhas Leakage?
Indian Ocean Zonally averaged Wind Stress τx (Nm-2)
± 2o
± 4o
± 20%
± 40%
± 2o
± 4o
± 20%
± 40%
Trad
es
We
ste
rlie
s Wind Stress (Nm-2)
Design considerations.
• (Intensities) Geometric. • (Shifts) Constant energy input. • No abrupt change in curl. • Anomalies only applied to τx. • No change over Agulhas Current latitudes
(32–35oS).
50 years SPIN-UP
Application of wind anomaly
Analyse 20 years Mean-State
Climatologically forced CORE dataset (Large & Yeager, 2009)
10 years adaptation
Leakage Dependency
Agulhas Current
Inertia at Separation
Leakage v/s Position
Leakage v/s Intensity
Resolution independent
Trades change ≡ Change in Inertia ≠ Leakage change
Equator Pole
Strong Weak
Anomalies to Trades
More details: [email protected]
Anomalies to Westerlies
Leakage v/s Position
Leakage v/s Intensity
Equator Pole
By construction, NO change in Agulhas Current Transport
Westerlies change ≡ Leakage change
Strong Weak
Leakage Dependency
More details: [email protected]
Change in Trades (position and intensity)
Change in Agulhas Transport
NO Change in Agulhas Leakage
1
3 Resolution has little effect Long term average
2 Change in Westerlies
(position and intensity) Pronounced Change in
Agulhas Leakage
Local Change Direct & Symmetric
Basin-wide Change
Weak Westerlies
Strong Westerlies
decrease Leakage
increase Leakage
decrease Leakage
increase Variability
More details: [email protected]
