Julien Emile-GeayJulien Emile-Geay

withMark Cane, Richard Seager, Amy Clement, Naomi Naik

and Alexander van Geen

Warren revisited : atmospheric freshwater fluxes and Warren revisited : atmospheric freshwater fluxes and “Why is no deep water formed in the “Why is no deep water formed in the

North Pacific ?”North Pacific ?”

THC

“A notable and well-known asymmetry in the deep ocean circulationis that deep water forms in the North Atlantic, and not at all in the North Pacific” (adapted from Bruce Warren)

What keeps deep water from sinking in the nNP ?

Why is the nNP so fresh relative to its Atlantic counterpart?

VBS,SSss

VWB,SSWBWB

Vu,SSuu

VN,SSWBWB VS,SSss

F=P-E

V’S’Eddy salt fluxes

Interior flow :VN –VS ≈ Sverdrup transportSalt transport MS= SWBVN – SsVS

Runoff

Western Boundary

flow

SWB ~ 34 psuSu = 34.6

V’S’

H=200m

A box model for the nNPA box model for the nNP(based on Warren 1983)(based on Warren 1983)

?

Conservations equations :Conservations equations :

• Freshwater budget :

€

R + F + Vu + Vwb = VBS + (VN −VS )

Interior flow = VN - VS

VWB is computed as a residual

• Salt budget (southward VWB) :€

SuVu+SWBVN+V'S'+W'S'=Ss[VBS+VS−VWB]

Eddy salt fluxes Outflow V0

Interior salt flux MS = SWBVN - SsVS

Subtropical inflowUpwelling

Results and sensitivity analysis

€

Ss =Fs

V0

≈160

4.8×10−3 = 32.93psu

Seasonal freshwater budget

Solid line :nNP

Dash-dotted :nNA

Thin solid :nNP-nNA

Why is the nNP so rainy despite its low evaporation rate?

WINTER

Moisture is pickedfrom the Warm Pooland converged into the nNP

€

rM (x, y) =

1

g(uq,vq) dp

1000

300

∫

SUMMER

Most of the northwardmoisture transport is associated with the Asian Monsoon

€

rM (x, y) =

1

g(uq,vq) dp

1000

300

∫

Conclusions

•Warren was essentially right : small throughflow rate and large (P-E) make the nNP so fresh• But it’s P, not E : Large atmospheric moisture transports, especially the Asian Monsoon, seem to explain this excess (in NCEP at least).

Why this is not happening in the North Atlantic : • different land/sea configuration (weaker Monsoon)• skinnier basin

Ultimately, the asymmetries of the land-sea configuration can explain THC asymmetries

Mass balance at the Southern Boundary

Warren’s box model (1983) CONFUSINGWarren’s box model (1983) CONFUSING : :

Freshwater fluxes :•F=P-E•R

+ Eddy Transports ..

Julien Emile-Geay:

Julien Emile-Geay:Julien Emile-

Geay:

Julien Emile-Geay:

VBS,SSss

VWB,SSWBWB

Vu,SSuu

VN,SSWBWB VS,SSss

F=P-E

A box model for the nNPA box model for the nNP(based on Warren 1983)(based on Warren 1983)

V’S’Eddy salt fluxes

Interior flow :VN –VS ≈ Sverdrup transportSalt transport MS= SWBVN – SsVS

Runoff

Western Boundary

flow

SWB ~ 34 psuSu = 34.6

V’S’ D =200m