1. Average circulation, seasonal cycle and mesoscale dynamics of the Peru Current System: A modeling approach Pierrick Penven (IRD), Vincent Echevin (IRD), Jose Pasapera (IMARPE), Jorge Tam (IMARPE) Chlorophyll 'a' - January 2002

2. 1. Introduction 2. Model configuration 3. Annual mean circulation 4. Seasonal cycle 5. Eddies

3. CALIFORNIA AND HUMBOLDTCANARY CURRENT 0.1% of the surface of the Oceans, BUT almost 30% of the world's fish catch California Current Humboldt Current Canary Current Benguela Current Surface chlorophyll concentration (source SeaWiFS & CZCS, NASA/Goddard Space Flight Center) 1.1 : The 4 principal upwelling systems

4. 1.2 : Upwelling in Peru Annual mean wind stress (10 -2 Pa) Sea Surface Temperature ( o C) April-June 2002 Chlorophyll 'a' - January 2002 The Humboldt Current System: - The most productive of the eastern boundary current systems - 18-20 % of the total worldwide marine fish catch - Permanent upwelling (max in winter) - Lack of narrow fronts and strong jets - Proximity and direct connection with the equatorial Ocean - Subjected to a dramatic interannual ENSO variability

5. 1.3 : The Peru Current System Peru Coastal Current (PCC) ● Cold and salty water ● Equatorial cold tongue Peru Chile Undercurrent (PCUC) ● Max velocity: 15 cm.s -1 ● 100-150 m ● Extends 600-700 m deep Peru Chile Counter Current (PCCC) ● Max velocities of 10 cm.s -1 ● 50 m Peru Oceanic Current (POC) ● From the surface to 700m Oceanic circulation scheme, adapted from Gunther [1936], Wyrtki [1963], Wyrtki [1967], Tsuchiya [1985], Lukas [1986], Huyer et al. [1991], and Strub et al. [1998].

6. 1. Introduction 2. Model configuration 3. Annual mean circulation 4. Seasonal cycle 5. Eddies

7. 2.1 : The model Physical model: ROMS (free surface, s-coordinate, high order schemes,...) Rectangular grid Horizontal resolution: 1/9° (~ 10 km) Number of points: 192 X 256 X 32 Bathymetry: ETOPO2 Surface forcing: COADS (monthly climatology), and QuickSCAT(October 1999 - March 2003) Boundary conditions: OCCAM (Global ocean model) Cyclic year (no el niños) Model bottom topography (m)

8. 2.2 : spin up Statistical equilibrium after 3 years - Strong increase in the SEC (from 50 to 80 cm/s) - In conjunction with the intrusion of tropical water (annual El-Nino current).

9. 2.3 : Summer sea surface temperature ( o C) and surface currents

10. 1. Introduction 2. Model configuration 3. Annual mean circulation 4. Seasonal cycle 5. Eddies

11. Equatorial Current (25-40 cm.s -1 ) South Equatorial Current (10-15 cm.s -1 ) Peru Coastal Current (15-25 cm.s -1 ) Peru Oceanic Current 3.1: Annual mean surface circulation , Streamfunction (10 -4 m 2.s -1 ) : representation of the nondivergent component of the flow

12. Equatorial Undercurrent (20-30 cm.s -1 ) South Equatorial Undercurrent (10-20 cm.s -1 ) Peru-Chile Undercurrent (5-15 cm.s -1 ) Peru Subsurface Countercurrent (~ 5 cm.s -1 ) Peru Oceanic Current 3.2 : Annual mean subsurface (50m) circulation

13. 3.3 : Alongshore averaged from 13 S to 7 S (Central Peruvian Upwelling System) a) Along shore currents Agreement between ROMS and WOA 2001 Strange Humboldt current in OCCAM

14. b) Temperature WOA : strong subsurface thermocline absent in OCCAM Local restratification in ROMS : tends to reduce the bias

15. c) Salinity Few salinity biases ( ~ 0.1 PSU)

16. 3.4 : Alongshore currents (cm/s) Humboldt current Peru-Chile subsurface Counter Current Peru-Chile Undercurrent Depth of an homogeneous subsurface layer such as f/H=10 -7 s -1.m -1

17. 1. Introduction 2. Model configuration 3. Annual mean circulation 4. Seasonal cycle 5. Eddies

18. 4.1: SST - COADS: dQ/dSST - Limited seasonal cycle - Large scale : agreement - ROMS too cold North of the Equator - Winter : not enough Upwelling in ROMS - Summer & Fall : cold tongue in ROMS - Not enough Upwelling off Paracas

19. 4.2 : SSH seasonal anomalies (cm) - North of the equator: Large scale seasonal oscillation high SSH in winter low SSH in summer - Upwelling system: low SSH at the coast in winter (maximum wind) propagates offshore in spring replaces by high SSH in summer propagates offshore in fall

20. 4.3 : Alongshore currents (cm/s) - Paita (5 o S): Stronger seasonal cycle Faster PCUC in fall (20 cm/s) Outropping of the PCUC Higher Equatorward flow in summer (15 cm/s) - Callao (12 o S): Weaker seasonal cycle Stronger Humboldt current in spring (30 cm/s)

21. 1. Introduction 2. Model configuration 3. Annual mean circulation 4. Seasonal cycle 5. Eddies

22. 5.1 : Non seasonal eddy kinetic energy (cm 2 /s 2 ) Missing large scale equatorial variability Correct representation of locally generated eddies Paracas upwelling cell ? Eddies coming from the south ?

23. Okubo-Weiss criterion at 20 m (10 -12 s -2 ) Vorticity at 20m (10 -5 s -1 ) Bigger eddies in the North ? 5.2 : Eddies

24. 5.3 : Eddy length scales First zero crossing Auto-correlation functions of surface velocities anomalies: Averaged in 2 o X2 o boxes and in time : Eddies are bigger in the North

25. Averaged in time in 2 o wide latitude stripes 5.4 : Energy spectra Geostrophic turbulence : Injection of Energy k -3 cascade towards the small scales k -5/3 inverse cascade towards the large scales log(k) log(E) Injection of energy length scale increases in the North

26. Rossby radius along 85 o W Eddy length scale Injection length scale Scale of energy injection follows Rossby radius/2: baroclinic instability Eddy scale from autocorrelation functions follow the trend Implication for biology ?

27. Future... Another large scale model (ORCA) Inter-annual simulations (El-Niños, inter-decadal variations,...) Couplage with ecosystem models Analysis of lagrangian transport (fish eggs & larvae transport) Nested models for small regions