Submesoscale coherent eddy in Greenland Sea

NoClim II, module D (ProClim) WP1

’A mode of deep ventilation’

Discovered in GS during ESOP II (Gascard et al. 2002)

• A homogeneous water column, cold core• Vertical extension, 2000 m • The horizontal scale of 10 km• Stationary? Long-lived ?

Kasajima et al. (2006)

SCV observations

1997 May

2001 Oct.

2003 April

2003 May

2003 Sep.

Second eddy 2003 May

2001 March

2002 Aug.

References

Gascard et al. 2002Wadhams et al. 2002Wadhams et al. 2004 (the second one)Budeus et al.2004

Active migration in 2003

SCV Vertical ventilation? ? ?

Formation where does the core water come from?

(Migration where is it transported?)

Dissolution where is the core water finaly released?

(How about the life time ?)Measurements of the chemical tracers in the core in 2003

SF6, CFCs, nutrients, (carbon)Direct velocity measurements

with LADCP

SF6 profiles

outside of the eddy

Inside of the Eddy

SF6 measurements

2003 Sep.

1999 May

SF6 fmol/l

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.5

3

4

5

7.5

10

20

30

40

50

100

66 68 70 72 74 76 78 80

0

500

1000

1500

2000

2500

3000

3500

Latitude

Pre

ssur

e (d

b)

SECTION knorr : SF6 / Sigma 500 isolines overlayed / June 2002 - Section 1

0

0

0

0

0

0

0.25

0.250.5

0.5

0.75

0.75

1

1

1.25

1.5

1.75

22

2.5

2.5

2.5

3

3

1.75

4

1 23 4 5 6 7 8 9 10 1112 13 1415 16 17 18 19 20 21 22 23 24 25 2627 28 29 30 31 32 33

30.25 30.2530.3 30.3 30.3

30.35 30.3530.35

30.37

30.37

30.39

30.39

30.4

30.4

30.4130.42

30.43

30.44

30.44

30.44

30.45

SF6 fmol/l

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.5

3

4

5

7.5

10

20

30

40

50

100

71 72 73 74 75 76 77

0

500

1000

1500

2000

2500

3000

3500

Latitude

Pre

ssur

e (d

b)

SECTION jcr44 : SF6 / Sigma 500 isolines overlayed / Arcice section 1

0 0

0

0

0

000

0.25

0.25

0.25

0.250.25

0.50.5

0.50.50.5

0.750.75

0.750.75

1

1

1

1

111

1.25

1.25

1.25

1.5

1.5

1.75

1.75

2

2

22.5

3

3

3

3

4

4

457.5

10

0.25

0.25

1.25

1.25

7.5

1.25

1.5

1.51.5

20

1

26 27 28 29 30 31 32 34 3536 37 38 39 40 41 43 424445 464748 49 50 5152 53 54

30.25

30.2530.2530.330.35 30.37 30.39

30.39

30.4

30.41

30.41

30.42

30.42

30.43

30.44

30.44

30.44

30.45

30.45

1999 2002

Time evolution of SF6 diffusion

(From Mandags kollokvium by Truls)

75 N 75 N

Possible core water end-membersSurface water high CFCs, oxygen concentrations

core water is cold, water in winterSF6 water relatively high SF6 concentration

- 1.30 34.878 342 7.4 3.8 2.3

-1.0634.865 347 7.3 3.8 2.3

-0.8634.883 317 5.1 2.63.1

-0.9034.879 323 5.5 2.8 2.9

Mixture 1(20% SW + 80% GSAIW)

-0.9534.882 322 5.6 2.8 2.9

Mixture 2(20% SW* + 80% GSAIW)

-0.96 34.882 322 5.4 3.0 2.9

θ (°C) Salinity Oxygen (µmol kg-

1) CFC-11 (pmol kg-

1) CFC-12 (pmol kg-

1) SF6(fmol kg-1)

Eddy(Sep. 2003)

SW (NoClim cruiseApril 2001)

GSAIW (Sep. 2003) Possible SW*

(assumed)

SCV in 1999 Cold surface water in winter (cold core water, high CFCs, oxygen)Returned Atlantic Water (Little SF6)

SCV 2003Cold surface water in winter (cold core water, high CFCs, oxygen)Greenland Sea Arctic Intermediate Water

Not in the central GS

The parents waters are found in the central GS

High SF6 water is lifted up toward the surface and cooled

20 % cold surface + 80 % GSAIW

1999 SCV and 2003 SCV are not the same one

Life time is not several years

Unit : m/s

Black

Green

Red

BlueN-S section in SCV

SNN S

176 177 178 179

Direct velocity measurements by LADCP

(a) EW-comp.(b) NS-comp.

Geostrophic flow(EW-comp.)

(a) (b)

0.2m/s

-0.2m/s

0.3m/s

-0.2m/s

Budeus et al. 2004

Max. Speed 0.2m/s at the radius 9km

Angular velocity = vorticity x 1/2

Radial velocity

Azimuthal velocity

-f/2 = vorticity observed earlier

Vorticity is overestimated by including background flow

Vel. obsevation = -f/2 + back ground flow

SCV vorticity is assumed to be -f/2

Trajectory of SCV

Southward migration ?!?

x(t)= xo + Ut + R exp(iωt)

Mean flow radius

Vel. obsevation – (-f/2)

Average = mean flow

- mean flow = vertical shear flow

N S

176 177 178 179

The rotation axis is tilted

From the study of tropical cyclones ;

The effects of the background vertical shear on the cyclones

1. Tilts the rotation axis downshear.

2. Turns the moving direction (to the left from the shear vector)

x(t)= (xo+Ut+R exp(iωt)) ∙C ∙ A

The background shear turns the migration direction northward.

Shear effect

Shear vector

Mean flow θΦ

Vertical shear vector

C |Vshear|

A = cosΦ sinΦ -sinΦ cosΦ

SCV is formed in the Greenland Sea by the mixture of 20 % of cold surface water and 80 % of intermediate water.

The source of the core water isprincipally from the upper intermediate layer in the central GS.

Conclusion

The direct velocity measurements reveal high shear in the SCV, which plays an important role in the migration direction.

The background flow/shear has changedsince 2003?