Global Ocean Circulation (2) 1.Wind-driven gyre-scale circulation of the surface ocean and upper thermocline 2.Global heat and freshwater water transport,

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

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/

+ =

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

Everywhere between the maximum of the westerlies, and the maximum of the Trades, there is convergence of Ekman transport

wind

westerlies

easterlies

max. of westerlies

max. easterlies

zone of Ekman convergence

http://ferret.pmel.noaa.gov/nvods

wind

Positive implies ocean warming Warming everywhere – of course

Positive implies ocean warmingNegative implies ocean cooling

Net longwave is less in WPWP than in east yet water is warmer?

Positive implies ocean cooling Western boundary currents have greatest air-sea temperature difference

COADS monthly climatology http://ferret.pmel.noaa.gov/NVODS/servlets/dataset?catitem=18098

Positive implies ocean cooling Distribution largely follows SST

Shaded is net cooling

Shaded is net cooling Western boundary currents are all coolingEquator is warming – especially in the east

Shaded is net cooling

Shaded is net cooling

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)

http://ferret.pmel.noaa.gov/NVODS/servlets/dataset?catitem=5707

Bars show direct estimates from oceanographic cross-sections

Heat transport from ocean observations constrained by conservation principles

Atlantic has

northward heat

transport everywher

e

Atlantic heat transport is so different because there is a

vertical over-turning circulation that shows up clearly in patterns

of salinity

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

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?

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?

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.