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Instability in the STCC region

Instability in the STCC region. 20111014 alu. Background. Qiu and Chen 2010 JPO. 135E 140E. Res=0.1deg (~10km) Domain:130E~179.9W(180.1),3N~33.1N Grid size:502x302x71 Flat bottom: 2000m. WOA2001 monthly Temp & Saln. Zero transport(u, v=0) & free-slip BC. 27N ←. 33N ←.

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Instability in the STCC region

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  1. Instability in the STCC region 20111014 alu

  2. Background Qiu and Chen 2010 JPO

  3. 135E 140E Res=0.1deg (~10km) Domain:130E~179.9W(180.1),3N~33.1N Grid size:502x302x71 Flat bottom: 2000m WOA2001 monthly Temp & Saln

  4. Zero transport(u, v=0) & free-slip BC 27N ← 33N ← Flow Relaxation Scheme and sponge zone Periodic BC Periodic BC 9N ← Zero transport(u, v=0) & free-slip BC Flow Relaxation Scheme and sponge zone 3N ← 1st 360 days: strong relaxation for spinup 2nd 360 days: no relaxation except northern and southern boundaries for instability growing ↓ 130E ↓ 180E Set up monthly runs for the region 135E~140E

  5. 0-relax Snapshots(t=0) Mar Sep elevation u & temp section@137E

  6. Eddy kinetic Energy (averaged from 18N~25N) EKE0=eke at day 5

  7. Averaged in upper 100m Unit: 1/days Mar May Nov Sep Kobashi et al. fig3a Averaged from 20N~25N

  8. JPO,2011 Fig 3 Fig 4

  9. Kobashi et al. fig6 Thermal wind relation Kobashi et al. fig15

  10. Initial state(t=0) Aug Mar PV profile@137E dPV/dy @137E

  11. If II is close to 0, means it reaches the most necessary condition for instability. Integrated from z0 to z200

  12. Solid: u shear Dash: eke Qiu,1999 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 Color: u shear in unit cm/s (u=u_surf – u_300) Contours: u_surf (positive region indicates the STCC)

  13. Solid: u shear Dash: eke Qiu, 1999. fig10

  14. 10 regions x 12 months=120 cases

  15. Solid: u shear Dash: eke u_shear (u0-u300)

  16. u_shear VS mean growth rate STCC_130135 STCC_135140 STCC_140145 STCC_145150 STCC_150155 STCC_155160 STCC_160165 STCC_165170 STCC_170175 STCC_175180

  17. Instability analysis 從準地轉位渦平衡方程式出發 令總流場＝初始(背景) 流場+perturbed 流場, 代入上式整理 BT BC 得 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：

  18. Instability analysis

  19. u_shear VS mean growth rate Kobashi,2006,JGR

  20. BT VS BC • Y_integ: 18N:25N • Z_integ:-400:0

  21. BT VS BC • Y_integ: 18N:25N • Z_integ:-400:0

  22. Order analysis (in first 100 days) 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=0-400m Y=18-25N

  23. dLEKE/dt (color), LEKE(black contours), EKE(red contours) case: stcc_135140, new def., upper 100m Jan May Sep Feb Jun Oct Mar Jul Nov APR Aug Dec

  24. EKE(average Upper 100m, 18N~25N, zonally)

  25. LEKE=log(EKE/EKE0), EKE0=eke at day 5

  26. dudy_uprof(11pt-smooth), stcc_135140

  27. 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.

  28. 從準地轉位渦平衡方程式出發 令總流場＝(背景)初始流場+perturbed 流場, 代入上式整理 得 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：

  29. 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

  30. Quantification of the movement of NEC (tail) The NEC tail extends to the northmost in Jan and retreat to the southmost in Sep Color: zonal averaged u at 200m (t=0), in unit cm/s. Contours: u = -5.5cm/s Red dot line: the exact position in latitude of the movement of the NEC(tail) in each month

  31. Bo Qiu,1999 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 Color: u shear in unit cm/s (u=u_surf – u_300) Contours: u_surf (positive region indicates the STCC)

  32. Jan May Sep Feb Jun Oct Mar Jul Nov APR Aug Dec

  33. d/dy(PV) , u, and temp Jan May Sep Feb Jun Oct Mar Jul Nov APR Aug Dec

  34. d(LEKE)/dtyt-plots

  35. Jan May Sep Feb Jun Oct Mar Jul Nov APR Aug Dec

  36. u shear VS u surface(130E~180E 10 cases) Color:u shear [u0-u300] (cm/s) Contour:u surface (cm/s)

  37. 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])

  38. BT VS BC • Y_integ: 18N:25N • Z_integ:-400:0

  39. BT VS BC • Y_integ: 18N:25N • Z_integ:-400:0

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