Agulhas Leakage in the CCSM4 - CESM · Operated by Los Alamos National Security, LLC for NNSA Slide...
Transcript of Agulhas Leakage in the CCSM4 - CESM · Operated by Los Alamos National Security, LLC for NNSA Slide...
![Page 1: Agulhas Leakage in the CCSM4 - CESM · Operated by Los Alamos National Security, LLC for NNSA Slide 1 Agulhas Leakage in the CCSM4 Wilbert Weijer (LANL) Erik van Sebille (UNSW, Sydney)](https://reader031.fdocuments.in/reader031/viewer/2022022716/5c160fef09d3f2946a8be30f/html5/thumbnails/1.jpg)
Operated by Los Alamos National Security, LLC for NNSA
Operated by Los Alamos National Security, LLC for NNSA Slide 1
Agulhas Leakage in the CCSM4
Wilbert Weijer (LANL)
Erik van Sebille (UNSW, Sydney)
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Operated by Los Alamos National Security, LLC for NNSA Slide 2
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Current Classical Western Boundary Current (like Gulf Stream, Kuroshio, etc.)
Closes subtropical wind-driven gyre of South Indian Ocean
Stramma & Lutjeharms (1997)
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Operated by Los Alamos National Security, LLC for NNSA Slide 3
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Current Classical Western Boundary Current (like Gulf Stream, Kuroshio, etc.)
Closes subtropical wind-driven gyre of South Indian Ocean
Stramma & Lutjeharms (1997)
Continental termination
Zero wind stress curl
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Operated by Los Alamos National Security, LLC for NNSA Slide 4
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Current: Retroflection Agulhas Current undergoes Retroflection
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Operated by Los Alamos National Security, LLC for NNSA Slide 5
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Current: Retroflection Agulhas Current undergoes Retroflection
Retroflection is unstable • Periodic shedding of Agulhas Rings (~ 6 rings per year)
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Operated by Los Alamos National Security, LLC for NNSA Slide 6
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Ring Shedding Agulhas Rings filled with warm and salty water
• Drift into South Atlantic: Agulhas Leakage
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Operated by Los Alamos National Security, LLC for NNSA Slide 7
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Super Gyre
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Operated by Los Alamos National Security, LLC for NNSA Slide 8
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Global Impact Gordon (1985)
• “Such a warm water link between the Atlantic and Indian oceans would strongly influence global climate patterns”
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Operated by Los Alamos National Security, LLC for NNSA Slide 9
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Global Impact Gordon (1985)
• “Such a warm water link between the Atlantic and Indian oceans would strongly influence global climate patterns”
Weijer et al. (1999, 2001, 2002) • Heat and salt injection through Agulhas Leakage
— Strengthens MOC — Stabilizes MOC
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Operated by Los Alamos National Security, LLC for NNSA Slide 10
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Global Impact Biastoch et al. (2008)
• High-resolution model of Agulhas region, nested in global model • “Dynamical signals from Agulhas region contribute MOC signal of same order of
magnitude as those arising in the north”
Biastoch et al. (2008)
With Agulhas variability
Without Agulhas variability
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Operated by Los Alamos National Security, LLC for NNSA Slide 11
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Implications How will Agulhas Leakage change in warmer climate?
• Poleward shift of wind belts
How will this affect the MOC?
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Operated by Los Alamos National Security, LLC for NNSA Slide 12
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage: Implications How will Agulhas Leakage change in warmer climate?
• Poleward shift of wind belts
How will this affect the MOC?
How is Agulhas Leakage represented in state-of-the-art Climate Model?
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Operated by Los Alamos National Security, LLC for NNSA Slide 13
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
Lagrangian analysis • CCSM4 20th century runs • Monthly 3D velocity fields, 1980-2005 • Release 110,000 numerical floats in Agulhas Current
— How many make it into South Atlantic? — How many make it across 21°S?
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Operated by Los Alamos National Security, LLC for NNSA Slide 14
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
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Operated by Los Alamos National Security, LLC for NNSA Slide 15
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
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Operated by Los Alamos National Security, LLC for NNSA Slide 16
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
Agulhas Current transport
69 Sv
70 Sv (Bryden et al. 2005)
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Operated by Los Alamos National Security, LLC for NNSA Slide 17
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
Good Hope line transport
43 Sv
14-17 Sv (Doglioli et al. 2006; van Sebille et al. 2009; Richardson 2007)
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Operated by Los Alamos National Security, LLC for NNSA Slide 18
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
21ºS transport
10 ± 1 Sv
10 Sv (Donners and Drijfhout 2004)
4 Sv (Biastoch et al. 2009)
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Operated by Los Alamos National Security, LLC for NNSA Slide 19
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4
3.6 ± 1.3 Sv/decade
-0.1 ± 0.6 Sv/decade
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Operated by Los Alamos National Security, LLC for NNSA Slide 20
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4 Agulhas Current okay
Agulhas Leakage overestimated by factor 3
Recirculates in super-gyre
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Operated by Los Alamos National Security, LLC for NNSA Slide 21
Operated by Los Alamos National Security, LLC for NNSA
Agulhas Leakage in CCSM4 Agulhas Retroflection inertial process
Not captured by low-resolution 1° models
Instead, leakage takes place in viscous boundary layer
De Ruijter (1982)
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Operated by Los Alamos National Security, LLC for NNSA Slide 22
Operated by Los Alamos National Security, LLC for NNSA
Does Agulhas Leakage influence MOC in CCSM4?
Leakage influences MOC through salinity anomalies • Actual volume flux irrelevant
Reference time series: S34S • Salinity averaged over upper 1000 m • In southeastern South Atlantic
Look for • Coherence between S34S and MOC • Correlations between S34S and anywhere else
X
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Operated by Los Alamos National Security, LLC for NNSA Slide 23
Operated by Los Alamos National Security, LLC for NNSA
Coherence of the AMOC with S(34S)
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Operated by Los Alamos National Security, LLC for NNSA Slide 24
Operated by Los Alamos National Security, LLC for NNSA
Coherence of the AMOC with S(34S)
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Operated by Los Alamos National Security, LLC for NNSA Slide 25
Operated by Los Alamos National Security, LLC for NNSA
Joint response to ENSO: AMOC
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Operated by Los Alamos National Security, LLC for NNSA Slide 26
Operated by Los Alamos National Security, LLC for NNSA
Signal propagation: lagged correlation
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Operated by Los Alamos National Security, LLC for NNSA Slide 27
Operated by Los Alamos National Security, LLC for NNSA
Signal propagation: lagged correlation
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Operated by Los Alamos National Security, LLC for NNSA Slide 28
Operated by Los Alamos National Security, LLC for NNSA
Signal propagation: lagged correlation
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Operated by Los Alamos National Security, LLC for NNSA Slide 29
Operated by Los Alamos National Security, LLC for NNSA
Signal propagation: lagged correlation
∆S = 0.24 psu
σ(S34S) = 0.11 psu
∆S = -0.04 psu
σ(S34S) = 0.02 psu
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Operated by Los Alamos National Security, LLC for NNSA Slide 30
Operated by Los Alamos National Security, LLC for NNSA
Conclusions
Agulhas Leakage too strong in CCSM4 • Factor of 3 • Too strong coupling between South Atlantic and Indian Oceans (“super gyre”) • Salinity too homogeneous
No discernible impact of Agulhas Leakage variability on MOC • Salinity variability too weak • Study is inconclusive
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Operated by Los Alamos National Security, LLC for NNSA Slide 31
Operated by Los Alamos National Security, LLC for NNSA
Meridional Coherence of the AMOC
T > 50 yr
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Operated by Los Alamos National Security, LLC for NNSA Slide 32
Operated by Los Alamos National Security, LLC for NNSA
Good Metric of Agulhas Leakage Impact?
X