17.5

17.5

17.517.518.5

18.5

18.5

18.5

SST from Feb 12, 2007

-70 -65 -60 -55 -5035

36

37

38

39

40

41

42

43

44

45

5

10

15

20

25

Upstream section(11-13/Feb)

Downstream section (18-23/Feb)

ASIS recover (23/Feb)

ASIS launch(13/Feb)

Test (10/Feb)

ASIS (17-Feb)

All observation points

speed (u2+v2)1/2

with from AMP; velocities from 75kHz ADCP (vertical resolution 20m). Black dashed line is depth of mixed layer defined by =0.1°C.Mixed layer is shallower toward the GS.

Richardson number

Upstream section

21196 21184 21196 21184

26 28 30 32 34 36 38

1

2

3

4

5

6

/ kg m-3 (off set +1.0 kg m-3)

dep

th[M

Pa]

-10 0 10 20 30 40 50

1

2

3

4

5

6

log10

/ W kg-1 (off set +log10

(5) W kg-1)

dep

th[M

Pa]

North SouthGSDeepest mixed layer

turbulent patchevery 50-80m

Deep enhanced mixing (K~10-2m2/s)

Estimate entrainment flux

Heat and buoyancy flux across the base of mixed layer

J be

nt /

W k

g-1qe

nt /

W m

-2

entbJ

zKCq w

ent

Cw: specific heat

: mixing efficiency (0.2)

26 28 30 32 34 36 38

1

2

3

4

5

6

/ kg m-3 (off set +1.0 kg m-3)

dep

th[M

Pa]

-10 0 10 20 30 40 50

1

2

3

4

5

6

log10

/ W kg-1 (off set +log10

(5) W kg-1)

dep

th[M

Pa]

050100150200250300-200

-100

0

cumulative distance from south[km]

05010015020025030010

-9

10-8

10-7

cumulative distance from south[km]

log10(K) / m2 s-1log10()/ W kg-1

Average , p >1.3MPa Average K, p >1.3MPa

Averaged values increase around the GS

21196 211842119621184

05010015020025030010

-5

10-4

10-3

Mixing is weak in vertical shear by the GS.

Mixing patches in south of the GS could be important for mode water formation.

05010015020025030010

-9

10-8

10-7

Comparison of K below mixed layer with KPP parameterization (estimated from observed Ri)

KPP parameterization tends to overestimate K in high shear due to the GS and underestimate Kin enhanced mixing patches due to internal waves.

observation KPP

17.5

17.5

18.5 18.5

18.5

18.5

SST from Feb 17, 2007

-61 -60.5 -60 -59.5 -59 -58.5 -5836

36.5

37

37.5

38

38.5

39

39.5

40

5

10

15

20

25

AMP21198 AMP21200

AMP21199

AMP21201

AMP21202-21203

AMP21204

ASIS (AMP 21198-21204)

ASIS section (Mixed layer formation)

47.26 47.46 47.79 47.90 47.91 47.99

47.18 47.26 47.46 47.79 47.90 47.91 47.99

26.2 26.3 26.4 26.5 26.6 26.7 26.8 26.9 27

0

1

2

3

/ kg m-3 (off set +0.1 kg m-3)

dept

h[M

Pa]

-10 -5 0 5 10 15 20 25

0

1

2

3

log10

/ W kg-1 (off set +log10

(5) W kg-1)

dept

h[M

Pa]

yday=47.18

ASIS section (Time series: Mixed layer formation)

Simple density budget(assuming time-series and 1D balance)

Simple one-dimension density budget

dttJgtD

t b

t

t

0

11

1

0

1

Density change due to surface buoyancy flux

It account for density change 0.013 kg m-3

against 0.06 kg m-3.

26.2 26.25 26.3 26.35 26.4 26.45 26.5 26.55 26.6 26.65

0

1

2

3

4

5

6

/ kg m -3

dept

h[M

Pa]

first profile last profile

density profileestimated above

D(t1)

A detail on mixed layer formation (AMP21203)

18.5 18.55 18.6 18.65 18.7 18.75 18.8 18.85 18.9

0

0.5

1

1.5

2

2.5

3

/ °C

p /

MP

a

36.6 36.605 36.61 36.615 36.62 36.625 36.631000*s

26.25 26.3 26.35 26.4 / kg m-3

-10 -9 -8 -7 -6 -5

log10( / W kg -1

inversion

Jb0

Clockwise rotation is observed in the base of mixed layer. Vertical shear is large around the density inversion.

-0.6 -0.3 0 0.3 0.6velocity[m/s]

u:blue line, v:red line

convection

convection?

entrainment(by convection or shear?)

increasing in mixed layer

17.5

17.5

17.5

17.5

17.5

18.5

SST from Feb 20, 2007

-57 -56 -55 -54 -53 -5236

36.5

37

37.5

38

38.5

39

39.5

40

40.5

41

5

10

15

20

25

downstream section (AMP21205-21209, 21211)

ASIS recover (AMP21210)

AMP21205

AMP21206

AMP21207

AMP21208

AMP21209

AMP21211

Downstream section

Downstream section

26.6 26.8 27 27.2 27.4 27.6 27.8 28 28.2 28.4 28.6

0

2

4

6

8

/ kg m-3 (off set +0.4 kg m-3)

dept

h[M

Pa]

-10 -5 0 5 10 15 20

0

2

4

6

8

log10

/ W kg-1 (off set +log10

(5) W kg-1)

dept

h[M

Pa]

North SouthGS51.02 51.12

yday=50.79 53.95 49.27 48.99

Deepmixed layer

Deep enhanced mixing

Deep mixed layer in the Gulf Stream (AMP21209)

14 16

0

1

2

3

4

5

6

p /

MP

a

36 36.5

26.6 26.8

-0.3 0 0.3 0.6 0.9

Velocity / m sec -1-8 -6 -4

N2,Shear2 / s -2-10 -9 -8 -7 -6 -5

/ W kg -1-5 -4 -3 -2 -1 0

K / m2 s-1

Convection and shear-driven entrainment could be mixed-layer deepening processes.

/ °C

1000*s

/ kg m-3

Jb0

u

v

N2

shear2

log10

u-shear v-shear

shear squared