Modeling China Sea Circulation: Kuroshio-Seas

transport

J. Gan

Collaborators: A. Cheung, Z. Liu and L. Liang

1

Outline:

•General circulation and model-observation comparisons in CS

•Kuroshio-East China Sea Transport

•Discussion

3

HK

<1km

<10km

South China Sea Basin

ContinentalShelf of SCS

Pearl RiverEstuary

HK

HK

<3km

HKUST China Sea Multi‐Scale Modeling System

120 121 122 123 124 125

28

29

30

31

32

33

34

longitudela

titud

e

Δ=Δ

<3km <1km

ECS shelf

CJ Estuary

Shanghai

ShanHai

<10km

<7km

ROMS, Real-time nesting with external fluxes using an OBC (Gan and Allen, 2005), QuickSCAT wind and NCEP atmosphere fluxes

4

SCS

ECS

Climatology Run

Direct simulation for 2009-2009

East China Sea

South China Sea

5

Surface geostrophic velocityWinter (2007-2009)

W1

W2

W3

W1

W2

W3

Model Observation

6

S1 S1

S2 S2

Surface geostrophic velocity

Summer (2007-2009)

Model Observation

7

winter

Modeled Observation

summer

(2007-2009)

W1

W2

W3

W1

W2

W3

S1

S2

S1

S2?

8

Modeled total velocity sd

summerwinter

spring fall

W1

W2

W3

S1

S2

9

10

River inputRiver input

Atmosphere COAtmosphere CO22

sinkingsinking

Microbialrecycling

sedimentsCoupled physical-biogeochemical processes in estuary and coastal ocean play a significant role in global ocean carbon cycling.

zooplankton

phytoplankton

Boundary exchangeBoundary exchange

IntraIntra--system transfersystem transfer

Carbon poolCarbon pool

Biological pump compositionBiological pump composition

ReRe--suspensionsuspension

DICDIC

Euphonic layer

DOCDOC

POCPOC

POCPOC

Deep 

Ocean

Coastal upward motion

Exchange with ocean

Biological pump

Terrestrial inputHigh biomassShallow waterFast sinking

AB

C

cs10.r

120 121 122 123 124 125 126 127 128 129 130 131 13223

24

25

26

27

28

29

30

31

32

33

34

AVISO

120 121 122 123 124 125 126 127 128 129 130 131 13223

24

25

26

27

28

29

30

31

32

33

34

vorticity<0vorticity>0

A: Exchange with Open Ocean

Observation

Model

2007-2009average

S

T

KECS

Q

P

11

Taiw

an

Taiw

an

Yangtze

2007 2007.5 2008 2008.5 2009 2009.5 20105

6

7

8

9

10

11

12 x 104

years

alon

g-ax

is tr

ansp

ort (

×104 m

2 /s)

AVISO

2007 2007.5 2008 2008.5 2009 2009.5 20105

6

7

8

9

10

11

12 x 104

years

alon

g-ax

is tr

ansp

ort (

m2 /s

)

cs10.9r

Observed

Model

Kur

oshi

o Su

rfac

e Fl

ux

Kur

oshi

o S

hore

war

d In

trus

ion

(Sur

face

)

5

0

5

10

ores

ide

boun

dary

tran

spor

t(×

104 m

2 /s)

5

0

5

10

ores

ide

boun

dary

tran

spor

t(×

104 m

2 /s)

Observed

Model

2007 2007.5 2008 2008.5 2009 2009.5 2010-3

-2

-1

0

1

2

3

4

5

6

years

diffe

renc

e of

alo

ng-a

xis

trans

port

(×10

4 m2 /s

)

Total - Geo

2007 2007.5 2008 2008.5 2009 2009.5 2010-15

-10

-5

0

5

10

15

years

diffe

renc

e of

cro

ss s

hore

side

bou

ndar

ytra

nspo

rt (×

104 m

2 /s)

Total - Geo

V-Vg

Model

U-Ug

Model

Surface Ekman Surface Ekman

shoreside

seaside

wintersummer winter

summer12

13

Taiw

an

China

Korea

Japan

seaward

T1

T2

T1

T2

T1-T2

Net volume change in ECS

Intrusion of Kuroshio

14

Taiwan Strait

Tsushima Strait

Shoreward intrusion

Summer Winter

intrusion

15

122 124 126 128 130-0.2

-0.1

0

0.1

0.2

shor

ewar

d ve

loci

ty(m

/s)

122 124 126 128 130-0.2

-0.1

0

0.1

0.2

shor

ewar

d ve

loci

ty(m

/s)

Observation Model

Shoreward intrusion

Shoreward intrusion

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T1

T2

Along T1 line

Along T2 line

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18

Taiwan Strait Mainland Taiwan Island

Summer

Winter

Pdownstream>Pupstream, intrusion occurs where isobaths are concave and Kuroshio turns anticyclonically.

P2

P1

isobath

P2>P119

Depth integrated velocity averaged from Dec. 2009 to Feb. 2009

temperature

salinity

PN

20

118o 119o 120o 121o 122o 123o 124o 125o 126o 127o 128o 129o 22o

23o

24o

25o

26o

27o

28o

29o

30o

31o

32o

33o

DH01DH02

DH03DH04

DH05

DH11

DH12

DH13DH21

DH21a

DH22

DH23

DH24

DH25

DH26

DH27

DH27b

DH31a

DH31bDH32

DH33

DH34

DH35

DH36

DH37DH51DH51a

DH51b

DH51c

DH52a

DH53

DH54

KP00KP01KP01a

KP07aKP04

KP13KP13aKP13b

PN03

PN03bPN04PN05PN06PN07PN08PN0PN10

YZ09

YZ-12a

YZ-02YZE YZEa

KP10a

F16

TW03

E

N

Temperature

Front formed between coastal waters and Kuroshio

~300km

Observation

Model Observation

Model21

DH01DH02

DH03DH04

DH05

DH11

DH12

DH13DH21

DH21a

DH22

DH234

DH31a

DH31bDH32

DH33

DH34

DH35

DH3651

PN03

PN03bPN04PN05PN06PN07PN08PN0PN10

YZ09

YZ-12a

YZ-02YZE YZEa

Current structure dominated by sub‐tidal current

Edge of Kuroshio

Model Observation

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front front

Modeled MVP PN07 – PN04

density

Summer 2009

temperature

salinity

118o 119o 120o 121o 122o 123o 124o 125o 126o 127o 128o 129o 22o

23o

24o

25o

26o

27o

28o

29o

30o

31o

32o

33o

DH01DH02

DH03DH04

DH05

DH11

DH12

DH13DH21

DH21a

DH22

DH23

DH24

DH25

DH26

DH27

DH27b

DH31a

DH31bDH32

DH33

DH34

DH35

DH36

DH37DH51DH51a

DH51b

DH51c

DH52a

DH53

DH54

KP00KP01KP01a

KP07aKP04

KP13KP13aKP13b

PN03

PN03bPN04PN05PN06PN07PN08PN0PN10

YZ09

YZ-12a

YZ-02YZE YZEa

KP10a

F16

TW03

E

N

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NO3 at 200 m

Winter

Luzon StraitInter-annual variation of Luzon transport

Enhancing intrusion

El Nino?

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AGE.

NL.

DIFF.

n

Intrusive current at Luzon Strait Mean net normal PGF (>0, westward)

Kuroshio

Ageostrophicterm

Nonlinear advection term

Dynamics of Intrusion

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SSHA along 20 N as function of time

C: 0.35-0.47 m/s

SSHA>0, KU geostrophically weakened

Surface elevation along 20 N as function of time

and intrusion is enhanced.

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2007 2008 20092007 2008 2009

2007 2008 20092007 2008 2009 27

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Kuroshio transport in ECS

Transport doesn’t drop in ECS!X

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Summary

Validated China Sea circulation model shows highly time- and space-coeherent transport in the directions along and cross Kuroshio at the edge of China Sea.

accel:prsgrd:Coriolis: hadv:sstr: bstr:hvisc:

2007 2008 2009

90days filter

Relax of wind stress leads to decrease of meridional pressure gradient

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Winter Spring Summer  Fall Annul

Taiwan Strait

0.61 2.24 3.03 0.56 1.6

TsushimaStrait

‐0.08 ‐1.38 ‐1.32 ‐0.64 ‐0.86

Shoreside 3.70 1.59 ‐0.07 0.39 1.4

NET 4.23 2.45 1.64 0.31 2.14

Seasonal and annual averages transport

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