1. Ocean Sciences Meeting, Salt Lake City, Utah, February 20-24, 2012
Ocean striations as a crossroad of multiple physics
Nikolai Maximenko
International Pacific Research Center
School of Ocean and Earth Science Technology
University of Hawaii
Collaborators and contributors: Oleg Melnichenko, Ali Belmadani, Emanuele Di Lorenzo,
and Niklas Schneider

2. Striations
in long-time mean zonal geostrophic velocity at the ocean surface, high-pass filtered horizontally with two-dimensional 4° filter.
cm/s

3. Smearing of eddy signal by time averaging
Schlax and Chelton, (2008) – Figure 2
Maximenko et al. (2005)
Scott et al. (2008)

4. Many striations seem to dynamically correspond to beta-plumes, induced by local vorticity forcing at their eastern tips
cm/s

5. Mean zonal geostrophic velocity at the ocean surface, high-pass filtered horizontally with two-dimensional 4° filter.
Azores current
cm/s
Kida, PhD: Azores current is a beta-plume induced
by overflow of Mediterranean water into
Atlantic

6. Mean zonal geostrophic velocity at the ocean surface, high-pass filtered horizontally with two-dimensional 4° filter.
Jets off California coast
cm/s
Centurioni et al, 2008: beta-plume induced
by interaction between mean Ekman flow and
stationary meanders

7. Mean zonal geostrophic velocity at the ocean surface, high-pass filtered horizontally with two-dimensional 4° filter.
cm/s

8. Sverdrup Vorticity Equation
HLCC: curl-driven zonal jet (slide courtesy of Belmadani)
Ekman flow: w
Sverdrup flow: V
Chavanne et al. 2002, CJRS
Sverdrup Vorticity Equation
Vorticity produced by vertical stretching + fluid turbulent stress.
Vorticity increased by moving poleward.
Ekman pumping
Curl drives Ekman pumping / suction.
Thermocline is lifted / depressed.
Cyclonic / anticyclonic eddies (e.g., Calil et al. 2008, DSR).
Sverdrup Balance
Meridional transport driven by curl.
Rossby waves propagate anomalies (e.g., Sasaki et al. 2010, OD).
Volume conservation: U
Nondivergent barotropic flow.
Barotropic Continuity Equation
Zonal transport to the west.
Integration from eastern boundary

9. Spatial-filtered SST & wind
HLCC: wind-forced β-plume (slide courtesy of Belmadani)
HLCC
NEC
HLC
Qiu et al. 1997, JPO
Curl > 0
V > 0
← Rossby waves
Cyclonic eddies
Western boundary
Island
Anticyclonic eddies
Curl < 0
V < 0
Elongated double-gyre west of Hawaii.
HLCC: narrow eastward jet embedded in broad North Equatorial Current (NEC).
β-plume (Rhines 1994, Chaos) = Sverdrup gyre driven by compact vorticity source (momentum, heat, mass).
HLCC = wind-forced β-plume (Jia et al. 2011, JGR).
Xie et al. 2001, Science
Other mechanisms: air-sea coupling, island-induced modified large-scale flow (Qiu Durland 2002, JPO), mode water intrusions (Sasaki et al. 2012, JO), etc.
Spatial-filtered SST & wind
HLCC advects warm SST → far-field curl dipole (Xie et al. 2001, Science; Hafner Xie 2003, JAS; Sakamoto et al. 2004, GRL; Sasaki Nonaka 2006, GRL, etc.).

10. Linear β-plume: steady-state barotropic solution (slide courtesy of Belmadani)τ
∇xτ
Wind: steady mesoscale anticyclonic vortex
, R = 40 km
Meridional transport: Sverdrup balance
, ρ = 1025 kg.L-1
β ≈ s-1m-1
Zonal transport: continuity equation
, xe ≈ 2890 km
Uana
ULIN
Good agreement between analytical and numerical solution.
1 anticyclonic cell (2 jets) + 2 weak cyclonic cells ⇒ 2+2 x-independent zonal jets.

11. Nonlinear β-plume: eddies and mean flow (slide courtesy of Belmadani)
SLNL
178ºE
178ºW
174ºW
170ºW
166ºW
162ºW
158ºW
154ºW
150ºW
38ºN
22ºN
30ºN
34ºN
26ºN
Yr 21
Yr 21-30
With stronger forcing, nonlinearities and instabilities grow, mesoscale eddies are shed from the forcing region.
Mean circulation is modified and becomes a dipole with 3 jets and a broader y-scale.

12. Heterogeneity of eddy trajectories
Schlax and Chelton (2008) – Figure 1

13. Heterogeneity of eddy trajectories
Schlax and Chelton (2008) – Figure 1

14. Space correlation functions of U’ and ζ’ reveal long zonal correlations and indicate that
eddies may be exaggerated and striations may be suppressed during mapping
From AVISO data
From AVISO mapping function

15. Effect of background meridional flow : advection
Linear regime
Nonlinear regime
Forcing
Forcing
k=(k,l) V0
Induction of
eddies by
forcing
Eddies
induced by
instability of
large-scale flow
Eddies
Induced by
instability of
striations

16. Tilt of striations correlates
with the direction of
background glow

17. Effect of background meridional flow : instability
Spall (2000): Generation of strong mesoscale eddies by weak ocean gyres
Stage 1: Instability of meridional flow produces strong zonal jets
Stage 2: Instability of zonal jets produces heterogeneous, isotropic eddies.

18. Formation of new eddies is not completely random
All
eddies
New
eddies
Histogram of anticyclones
relative to crests in striations
Histogram of cyclones
relative to troughs in striations

19. Concluding remarks:
1. Eddies are important (and most energetic) players in visualizing striated patterns.
2. Striations reflect higher organization of eddies (preferred paths, eddy trains, etc.).
3. Understanding striations may be more feasible through dynamical rather than kinematic study.
4. “Anchoring” processes that still need to be understood:
anchoring of source regions to topographic features;
anchoring of new eddy formation to striations;
possible fixation of western tips of striations;
air-sea interaction.