Instability in the STCC region
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Instability in the STCC region
20111014alu
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Background
Qiu and Chen 2010 JPO
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Res=0.1deg (~10km)Domain:130E~179.9W(180.1),3N~33.1NGrid size:502x302x71 Flat bottom: 2000m
135E 140E
WOA2001 monthly Temp & Saln
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Flow Relaxation Scheme and sponge zone
Flow Relaxation Scheme and sponge zone
33N ←
3N ←↓130E
↓180E
Periodic BC
Periodic BC
27N ←
9N ←
Zero transport(u, v=0) & free-slip BC
Zero transport(u, v=0) & free-slip BC
1st 360 days: strong relaxation for spinup2nd 360 days: no relaxation except northern and southern boundaries for instability growing
Set up monthly runs for the region 135E~140E
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0-relax Snapshots(t=0)Mar Sep
elevation
u & temp section@137E
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2'2' vuEKE
Eddy kinetic Energy (averaged from 18N~25N)
tEKEEKELEKE
eEKEEKE t
0
0
ln
1ln)(0
t
EKEEKEtLEKEDay foldinge
EKE0=eke at day 5
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RifGrowthRateEady 22
2
zv
zuNRi
Unit: 1/days
Mar May Sep
Nov
Averaged in upper 100m
Kobashi et al. fig3a
Averaged from 20N~25N
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Fig 3
JPO,2011
Fig 4
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Kobashi et al. fig6
Thermal wind relationKobashi et al. fig15
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Mar Aug
z
fyx
PV yxErtel
Initial state(t=0)
PV profile@137E
dPV/dy @137E
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Integrated from z0 to z200
dzyzyPVIIyIndexInstabilit ),()(
If II is close to 0, means it reaches the most necessary condition for instability.
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Color: u shear in unit cm/s (u=u_surf – u_300) Contours: u_surf (positive region indicates the STCC)
The pink region indicates the large u shear occurs in May, June, July. In these months, the strength of u shear is mainly contributed by upper layer STCC. However, the NEC starts retreating in these months, and the EKE analysis also shows the more stable conditions. So, the strengthening of STCC does not contribute to the instability
Qiu,1999
Solid: u shearDash: eke
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Qiu, 1999. fig10
Solid: u shearDash: eke
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1 2 3 4 5 6 7 8 9 10
10 regions x 12 months=120 cases
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u_shear (u0-u300)
Solid: u shearDash: eke
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STCC_135140
STCC_140145
STCC_145150
STCC_150155
STCC_155160
STCC_160165
STCC_165170
STCC_170175
STCC_175180
STCC_130135u_shear VS mean growth rate
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Instability analysis
2
12
12 0
LL
S
zS
zyQ
zS
zy
dtd
bcD
),,,(,,,, tzyxzytzyx
從準地轉位渦平衡方程式出發
zUf
ygM
zgNgb
dydzNMbv
yUvu
t
EKEdydz
refrefref
00202
2
20
,,
''''
令總流場=初始 (背景 ) 流場 +perturbed 流場 , 代入上式整理
zS
zy
y
yqJq
xU
t x
12
2
0
00 0,
得
zS
zyyq
yxqU
tq
x
12
2
2
2
00 0
假設 ||<<1, drop J(,q)項 , 考慮邊界條件 w*=w0+w1+O(^2) at surf and bott,整理得到:
000
dVyx
qUtq
x
BT BC
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Instability analysis
dydzyUvuBT 0''
dydzNMbvBC 2
2
''
BCBTdydzEKEt
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u_shear VS mean growth rate
Kobashi,2006,JGR
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BT VS BCY_integ: 18N:25NZ_integ:-400:0
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BT VS BCY_integ: 18N:25NZ_integ:-400:0
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Order analysis (in first 100 days)
dydzyUvuBT 0''
dydzNMbvBC 2
2
''
Order of BT=1*2*3= 1e-14
1. order of u’: 1e-3 2. v’: 1e-4 3. dU0dy:1e-7
Order of BC=1*2*3/4=1e-12
1. order of v’: 1e-4 2. b’: 1e-4 3. M2: 1e-8 Approach A:M2=f*dU0dz a.1 f: 1e-5 a.2 dU0/dz: 1e-3 Approach B:M2=g*d(rho0/rhoref)dy b.1 g: 1e1 b.2 d(rho0/rhoref)dy:1e-9 4. N2: 1e-4
Z=0-400mY=18-25N
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Jan Feb Mar APR
May Jun Jul Aug
Sep Oct Nov Dec
dLEKE/dt (color), LEKE(black contours), EKE(red contours)case: stcc_135140, new def., upper 100m
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EKE(average Upper 100m, 18N~25N, zonally)
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LEKE=log(EKE/EKE0), EKE0=eke at day 5
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dudy_uprof(11pt-smooth), stcc_135140
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Literatures• Qiu, 1999 JPO: Seasonal Eddy Field Modulation of the North Pacific
Subtropical Countercurrent: TOPEX/Poseidon Observations and Theory. • Kobashi et al, 2006 JGR: Three subtropical fronts in the North Pacific:
Observational evidence for mode water-induced subsurface frontogenesis
• Yamanaka et al, 2008 JGR: Decadal variability of the Subtropical Front of the western North Pacific in an eddy-resolving ocean general circulation model
• Qiu and Chen, 2010 JPO: Interannual Variability of the North Pacific Subtropical Countercurrent and Its Associated Mesoscale Eddy Field
• Xie et al,2011 JC: Dynamical Role of Mode Water Ventilation in Decadal Variability in the Central Subtropical Gyre of the North Pacific.
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2
12
12 0
LL
S
zS
zyQ
zS
zy
dtd
bcD
),,,(,,,, tzyxzytzyx
從準地轉位渦平衡方程式出發
zUf
ygM
zgNgb
dydzNMbv
yUvu
t
EKEdydz
refrefref
00202
2
20
,,
''''
令總流場= (背景 )初始流場 +perturbed 流場 , 代入上式整理
zS
zy
y
yqJq
xU
t x
12
2
0
00 0,
得
zS
zyyq
yxqU
tq
x
12
2
2
2
00 0
假設 ||<<1, drop J(,q)項 , 考慮邊界條件 w*=w0+w1+O(^2) at surf and bott,整理得到:
000
dVyx
qUtq
x
zUf
ygM
zgNgb
dydzNMbv
yUvu
t
EKEdydz
zS
zyyq
yxqU
tq
yq
xU
t
zS
zy
y
yqJq
xU
t
tzyxzytzyx
LL
S
zS
zyQ
zS
zy
dtd
refrefref
x
x
x
Dbc
00202
2
20
12
2
2
2
00
00
12
2
0
00
2
12
12
,,
''''
0
0
0,
),,,(,,,,
0
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Color: map of the max growth rate in the first year (1/days)Contours: when the max growth rate occur (days), thick contour indicates 100
The NEC tail extends to the northmost in Jan and retreat to the southmost in Sep
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Quantification of the movement of NEC (tail)
Color: zonal averaged u at 200m (t=0), in unit cm/s. Contours: u = -5.5cm/sRed dot line: the exact position in latitude of the movement of the NEC(tail) in each month
The NEC tail extends to the northmost in Jan and retreat to the southmost in Sep
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Color: u shear in unit cm/s (u=u_surf – u_300) Contours: u_surf (positive region indicates the STCC)
The pink region indicates the large u shear occurs in May, June, July. In these months, the strength of u shear is mainly contributed by upper layer STCC. However, the NEC starts retreating in these months, and the EKE analysis also shows the more stable conditions. So, the strengthening of STCC does not contribute to the instability
Bo Qiu,1999
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Jan Feb Mar APR
May Jun Jul Aug
Sep Oct Nov Dec
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d/dy(PV) , u, and temp
Jan Feb Mar APR
May Jun Jul Aug
Sep Oct Nov Dec
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d(LEKE)/dt yt-plots
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Jan Feb Mar APR
May Jun Jul Aug
Sep Oct Nov Dec
RifGrowthRateEady
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u shear VS u surface(130E~180E 10 cases)
Color:u shear [u0-u300] (cm/s)Contour:u surface (cm/s)
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u shear VS max_growth_rate(130E~180E 10 cases)
Color: u shear[u0-u300] (cm/s)Conotur: max_growth_rate (z=0-100avg)(0.05,0.1,0.15,0.2 [1/days])
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BT VS BCY_integ: 18N:25NZ_integ:-400:0
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BT VS BCY_integ: 18N:25NZ_integ:-400:0