Date post: | 14-Dec-2015 |
Category: |
Documents |
Upload: | brice-thomas |
View: | 220 times |
Download: | 0 times |
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?