Turbulence and Mixing in Shelf Seas John Simpson, Tom Rippeth, Neil Fisher,Mattias Green
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Transcript of Turbulence and Mixing in Shelf Seas John Simpson, Tom Rippeth, Neil Fisher,Mattias Green
Turbulence and Mixing in Shelf Seas
John Simpson, Tom Rippeth, Neil Fisher,Mattias Green Eirwen Williams, Phil Wiles, Matthew Palmer
Funded by the NERC, EU (OAERRE, MABENE, C2C) and Dstl
With technical support from Ray Wilton, Ben Powell& the officers and crew of the Prince Madog
.School of Ocean Sciences,
University of Wales Bangor, Menai Bridge,LL59 5EY, UK
Ysgol Gwyddorau Eigion,Prifysgol Cymru Bangor,
Porthaethwy
Visit our web site at:www.sos.bangor.ac.uk/research/tmiss/index.html
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• Motivation• Measurement capabilities
• Mapping ε in shelf regimes with FLY• ADCP variance method for Production
• Mixing in the pycnocline of the shelf seas
Turbulent processes in shelf seas
Motivation ?
• Key environmental control of:
Fluxes of nutrients/ particles etc. (Mixing) Particle aggregation/disaggregation
Predator-prey encounter rates
• Tests of Turbulence Closure schemes for models
zK
z
v
z
u
z
EK
zt
Ezxq y
Which Properties ? Diffusion TKE production Buoyancy Dissipation
ADCP Variance method
FLYDissipationProfiler
S1 M1
Mixed station M1 observed ε
ε Model MY2.2(with diffusion)
Model MY2.0(no diffusion)
Time(days)
Stratified station S1
T°C
ε (Wm-3)
ε Model MY2.2
ε observed
Model – Observation Inter-comparison
BIG discrepancy between the predicted (using MY2.2 closure scheme) and observed levels of (Simpson et al., 1996).
• ie. The model fails to reproduce the critical dissipation and thus mixing within the thermocline.Bottom
Boundary Layer
Log10 [0 (Wm-3)]
Model
Obs.
Missing physical processes within the model?
S1
z
z
Nzte
A
z
u
2);4/cos(2
))2/22cos(1(22
22
2
zteAN
z
uNP
zz
z
The velocity shear in a boundary layer forced by an oscillating pressure gradient X=A cos ωt
is given by (Lamb p.622):
The corresponding TKE production will be:
2/2
2/24 zN
zz
which increase with height above bed at a rate
zN
2
So that the production (and hence ε ) will exhibit an M4 phase lag of :
The phase of TKE production ?
Phase lag (hours)
Mixed Nz=0.4m2s-1
StratifiedNz=0.025m2s-1
PHASE AMPLITUDE
MixedNz=0.13m2s-1
Liverpool Bay ROFI
186.7 186.8 186.9 187 187.1 187.2 187.3 187.4 187.5 187.6 187.7
T em p era tu re (d eg ree s C )
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
1 4 .61 4 .71 4 .81 4 .91 5 .01 5 .11 5 .21 5 .31 5 .41 5 .51 5 .61 5 .71 5 .81 5 .91 6 .0
186.7 186.8 186.9 187 187.1 187.2 187.3 187.4 187.5 187.6 187.7
D ec im a l D ay
S a lin ity (P S U )
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
3 2 .4 5
3 2 .5 5
3 2 .6 5
3 2 .7 5
3 2 .8 5
3 2 .9 5
3 3 .0 5
3 3 .1 5
3 3 .2 5
3 3 .3 5
LB2
Temperature
Salinity
Cycle of epsilon with density
186.7 186.8 186.9 187 187.1 187.2 187.3 187.4 187.5 187.6 187.7
D ecim al D ays
0
5
10
15
20
25
30
35H
eigh
t abo
ve B
ed (
m)
-5.50
-5.00
-4.50
-4.00
-3.50
-3.00
-2.50
-2.00
-1.50
JPO 31,2458-2471 (2001)
Log W/m3
E p silo n (L o g1 0
W m - 3 )
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
-5 .5 0
-5 .0 0
-4 .5 0
-4 .0 0
-3 .5 0
-3 .0 0
-2 .5 0
-2 .0 0
-1 .5 0
186.7 186.8 186.9 187 187.1 187.2 187.3 187.4 187.5 187.6 187.7
D ec im a l D ay s
U /z (s - 1 )
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
-0 .0 4
-0 .0 3
-0 .0 2
-0 .0 1
0
0 .0 1
0 .0 2
O b se rv a tio n s - E p s ilo n (L o g1 0
W m - 3 ) w ith D en s ity co n to u rs (k g m - 3 )
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
-5 .5 0
-5 .0 0
-4 .5 0
-4 .0 0
-3 .5 0
-3 .0 0
-2 .5 0
-2 .0 0
-1 .5 0
186.7 186.8 186.9 187 187.1 187.2 187.3 187.4 187.5 187.6 187.7
D ecim al D ays
C A N U T O w ith N u d g in g -E p s ilo n (L o g1 0
W m - 3 ) w ith D en s ity co n to u rs (k g m - 3 )
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
-5 .5 0
-5 .0 0
-4 .5 0
-4 .0 0
-3 .5 0
-3 .0 0
-2 .5 0
-2 .0 0
-1 .5 0
GOT Model
k-epsilon +Canuto
Hans Burchard
Karsten Bolding
R a tio o f S h ea r P ro d u c tio n to D iss ip a tio n ra te .
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
186.7 186.8 186.9 187 187.1 187.2 187.3 187.4 187.5 187.6 187.7
D ec im a l D ay s
R a tio o f B u o y an cy P ro d u c tio n to D iss ip a tio n ra te .
0
5
10
15
20
25
30
35
Hei
ght a
bove
Bed
(m
)
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
-0 .50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
C A w ith N udging
P/ε
B/ε
ADCP Variance Method
z
v
z
uP yx
bbb coswsinvb 444
z
w4
v4
b4
4 3
y
2sin2
bb'w'v
23
24
y