Download - Young-oh Kwon et al
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Role of the Gulf Stream and Kuroshio-Oyashio Systems in Large-
Scale Atmosphere-Ocean Interaction: A Review
Young-oh Kwon et al.
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Outline
• Intorduction• Processes affecting the SST variability in the
WBCs• WBCs and the basin-scale climate variability• Performance of climate models on simulation
of WBC variability• Outstanding issue
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Introduction
• There are “exceptionally” strong atmosphere-ocean interaction over West Boundary Current region.– Mean and Variances(SSTA)– Interannual and longer time scale– Heat transport
• Atmosphere response to WBC STTAs with several issues
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Processes affecting the SST in WBC region
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Interesting issues
• The Connection between frontal-scale boundary layer ocean-atmosphere interaction and the basin-scale variability.
• Potential changes in WBC ocean duce to global warming.
• The relationship between the Meridional overturning circulation and Gulf Stream in North Atlantic.
• Interbasin connection between the KOE and GS variability.
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Processes affecting the SST variability in the WBCs
• Shift of oceanic fronts• Oceanic advection• Surface heat fluxes• Ekman transport• Reemergence mechanism• Remote wind stress curl forcing
communicated via oceanic Rossby wave• Tropical atmosphere teleconnections
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Shift of oceanic front
• Decadal SST variability is particularly strong along the SubArctic Frontal Zones.
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Oceanic advection
• In the WBCs on interannual and longer time scales is determined mainly by anomalous geostrophic advection, which tends to dominate over Ekman advection and Qnet.
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Surface heat flux
• Qnet in the WBC
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Ekman Transport
• Ekman transport responds quickly to changes in surface wind and can generate SSTA.
• To reinforce the Qnet in mid-latitudes because stronger westerlies cool the ocean by the sensible and latent heat fluxes and by southward Ekman transport.
• The cross-frontal cold Ekman advection lowers the near-surface stratification on the warmer side of the front and enhance vertical mixing.
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Reemergence mechanism
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Remote wind stress curl forcing communicated via oceanic Rossby
wave
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Tropical Teleconnection
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WBCs and the basin-scale climate variability
• Decadal SST variability in the WBCs• Oceanic dynamics and decadal variability• Surface heat flux damping and implications• Decadal variability in atmosphere-ocean
coupled general circulation models
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Decadal SST variability in the WBCs
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Oceanic dynamics and decadal variability
• As the Rossby waves propagate westward, they integrate the stochastic forcing to increase the variance and dominant period of dynamic ocean properties until reaching a maximum near the WBC.
• The spatial resonance mechanisms could generate a decadal peak in the ocean by stochastic atmosphere.
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Surface heat flux damping and implications
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Decadal variability in atmosphere-ocean coupled general circulation
models• Coupled climate models generally indicate
that ocean-atmosphere interaction in WBC regions is a key factor in generating extropical decadal variability.
• Although earlier studies suggested that North Atlantic decadal variability in SST was primarily reflecting a passive response to the atmospheric forcing.
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Performance of climate models on simulation of WBC variability
• High-resolution ocean simulations• Simulation of the Kuroshio and Gulf Stream at
non-eddy-permitting resolution• Atmospheric simulations
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High-resolution ocean simulations
• For KOE:– KE’s path variability can be tied largely to wind
forcing.
• For GS:– Interaction between DWBC.
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Simulation of the Kuroshio and Gulf Stream at non-eddy-permitting
resolution
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Outstanding issues
• How are the frontal-scale and basin-scale atmosphere-ocean interactions related?
• What is the large scale atmospheric circulation/wind stress curl response to the WBC SSTA
• Global warming and the WBCs• Relation between the Gulf Stream and the
MOC• Connection between GS and KOE variability