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Global Ocean Circulation (2)1. Wind-driven gyre-scale circulation of the
surface ocean and upper thermocline
2. Global heat and freshwater water transport, conservation properties
3. Water mass properties, polar convection and mixing, tracers, global thermohaline circulation
Focus on conservation principles:Balancing heat, salt, etc. into and out of boxes
© D
ong
lai G
ong
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Sea surface topography variationsPhenomenon Typical
Surface Expression
Period of Variability
Comments
Western boundary currents (Gulf Stream, Kuroshio)
130 cm/100 km Days to years Variability in position, and 25% variability in transport
Large gyres 50 cm/ 3000 km One to many years
25% variability expected
Eastern boundary currents
30 cm/100 km Days to years 100% variability expected, possible direction reversals
Mesoscale eddies
25 cm/100 km 100 days 100% variability
Rings 100 cm/100 km Weeks to years 100% variability, growth and decayEquatorial
currents30 cm/5000 km Months to
years100% variability
Tides 100cm/5000 km Hours to years Aliased to low frequency
http://jeffreyearly.com/science/qg-eddies-paper/
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+ =
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http://ferret.pmel.noaa.gov/nvods/UI.vm#panelHeaderHidden=false;differences=false;autoContour=false;globalMin=2.566;globalMax=29.03;xCATID=WOA_05_CAT;xDSID=woa05_monthly;varid=t0112an1;imageSize=auto;over=xy;compute=Nonetoken;tlo=16-Jan-0001;thi=16-Jan-0001;catid=WOA_05_CAT;dsid=woa05_monthly;varid=t0112an1;avarcount=0;ylo=21;yhi=21;xlo=110;xhi=260;ylo=21;yhi=21;zlo=0;zhi=1500;operation_id=Plot_2D_zoom;view=xz
http://ferret.pmel.noaa.gov/nvods/UI.vm#panelHeaderHidden=false;differences=false;autoContour=false;globalMin=2.566;globalMax=29.03;xCATID=WOA_05_CAT;xDSID=woa05_monthly;varid=t0112an1;imageSize=auto;over=xy;compute=Nonetoken;tlo=16-Jan-0001;thi=16-Jan-0001;catid=WOA_05_CAT;dsid=woa05_monthly;varid=t0112an1;avarcount=0;ylo=21;yhi=21;xlo=110;xhi=260;ylo=21;yhi=21;zlo=0;zhi=1500;operation_id=Plot_2D_zoom;view=xz
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Everywhere between the maximum of the westerlies, and the maximum of the Trades, there is convergence of Ekman transport
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wind
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westerlies
easterlies
max. of westerlies
max. easterlies
zone of Ekman convergence
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http://ferret.pmel.noaa.gov/nvods
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wind
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Positive implies ocean warming Warming everywhere – of course
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Positive implies ocean warmingNegative implies ocean cooling
Net longwave is less in WPWP than in east yet water is warmer?
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Positive implies ocean cooling Western boundary currents have greatest air-sea temperature difference
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COADS monthly climatology http://ferret.pmel.noaa.gov/NVODS/servlets/dataset?catitem=18098
Positive implies ocean cooling Distribution largely follows SST
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Shaded is net cooling
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Shaded is net cooling Western boundary currents are all coolingEquator is warming – especially in the east
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Shaded is net cooling
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Shaded is net cooling
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RT = Radiation total at the top of the atmosphere from Earth Radiation Budget ExperimentOT = ocean transport from net air-sea heat fluxAT = atmospheric transport (calculated from RT – OT)
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http://ferret.pmel.noaa.gov/NVODS/servlets/dataset?catitem=5707
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Bars show direct estimates from oceanographic cross-sections
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Heat transport from ocean observations constrained by conservation principles
Atlantic has
northward heat
transport everywher
e
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Atlantic heat transport is so different because there is a
vertical over-turning circulation that shows up clearly in patterns
of salinity
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South North
Low salinity in north but no large negative E-P. What other freshwater sources are there?
Where evaporation is strong we tend to
have high salinity
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Precipitation minus evaporation (m year-1)
Shaded implies net precipitation Earth’s water budget is dominated by P-E over the ocean (80% occurs
there) Max P-E in East Pacific is not exactly over the
equator – why?
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Surface Atlantic is saltier than the Pacific
Many large rivers drain into the Atlantic and the Arctic Sea, so why is the Atlantic saltier than the Pacific?
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Broecker (1997) showed that 0.32 Sv of the water evaporated from the Atlantic does not fall as rain on land. It is carried by winds into the Pacific.
The quantity is small, equivalent to little more than the flow in the Amazon River.
But were this flux not compensated by an exchange of more salty Atlantic waters for less salty Pacific waters, the salinity of the
Atlantic would rise about 1 gram per liter per millennium.