1. Variability of the Western Iberian Buoyant Plume to wind events Pablo Otero 1, Manuel Ruiz-Villarreal 1, Álvaro Peliz 2 and Jesús Dubert 2 1 Instituto Español de Oceanografía Muelle de las Ánimas s/n, 15002, A Coruña (Spain) 2 Departamento de Física, Universidade de Aveiro, 3810-194, Aveiro, (Portugal) pablo.otero@co.ieo.es 2006 ROMS/TOMS European Workshop Alcalá de Henares (Spain), November 6-8

2. How to? Hydrography of the area Analysis of freshwater discharge Design of the simulation Real forcing Isohaline coordinates Spatial variability Front detection Classification of the WIBP PREVIOUS KNOWLEDGE NUMERICAL MODEL ANALYSIS OF MODEL OUTPUTS

3. The downwelling season IPC Coastal Front River plume WIBP IPC Wind

4. Freshwater discharge Climatologic value and scale correction for Nov-Dec 2002. Inter-annual variability (and daily: reservoirs!) is a strong problem

5. ROMS (Regional Ocean Modelling System, Haidvogel et al., 2002) with nesting capability (Penven et al., 2004). Three grids with 15Km, 5Km, and 1.8Km 30 vertical s-layers. OSU tidal inverse model (Egbert and Erofeeva, 2002) Forcing (MM5: 30Km, 1h). 3 grids… …3 stages State-of-the-art

6. Circulation after the Prestige accident (Sea surface salinity from November 19th to 29th)

7. November-December 2002 Silleiro Buoy MM5 Case 1: Confinement (downwelling) Case 2: Expansion (relaxation) Case 3: Expansion (upwelling) REALISTIC SIMULATION DOWNWELLING UPWELLING

8. Case 1: Confinement (downwelling) SECTION Jet Smoothing River Douro River Miño Upwards Cape Fisterra 20Nov21Nov22Nov Enhanced slope current

9. Case 2: Expansion (relaxation) SECTION Jet 22Nov23Nov24Nov Weakness

10. Case 3: Expansion (upwelling) SECTION Meandering Northern limit Detachment Upwelling of slope current: Reported on the bottom of Rías Baixas Wind mixing Stratification

11. AVHRR 25Nov 3h ROMS 25Nov 3h Flooding event Climatologic discharge SW wind overestimated in earlier hours by MM5 Stronger surface signal of IPC Comparison to observations

12. SeaWiFS 5-7 Dec 2002 composite ROMS 6 Dec 2002

13. AUTOMATIC DETECTION OF RIVER PLUME FRONTS

14. Potential density Vertical gradient Maximum local value Map of Mixed layer depth Sobel Edge Filter Thresholding

15. Downwelling event

16. Relaxation of a downwelling event

17. ISOHALINE COORDINATES

18. Mixed layer depth River plume front Wind mixing Shear mixing Estuary Ocean Isohaline coordinates A coordinate method based in salinity Consider calculations between salinity classes (isohalines) Why? River plume as a system Temporal variability can be analysed neglecting spatial variability Problems? To delimit the plume, it is necessary to establish the ocean (‘ambient’) isohaline, and this is not obvious in a realistic study. Salinity classes S=0 0.10.2 0.30.4 35.535.6 River Ocean

19. Near field Far field Salinity classes Time DownwellingUpwelling Wind stress Total freshwater volume increases in time Downwelling winds -> accumulation of freshwater at lower salinity classes Confinement Upwelling winds -> displacement of freshwater at higher salinity classes Expansion and mixing Freshwater volume between isohalines

20. DownwellingUpwelling Near field Far field Salinity classes Time Wind stress Vertical salt flux responds immediately to wind changes -> key factor Vertical salt flux is higher at higher salinity classes

21. PHYSICAL CLASSIFICATION

22. Physical parameters Froude Kelvin Slenderness Plume depth Mean density Inertial radius Scaled Ekman transport Scaled basal friction Residence time […]

24. Conclusions Variability of the Western Iberian Buoyant Plume (WIBP) is described with high spatial and temporal resolution (scale of hours) WIBP responds asymmetrically to upwelling and downwelling wind events, with an along-shore circulation during downwelling or steady state and with across-shore circulation during upwelling wind events (south-westwards off the mouth of main rivers). The Iberian Poleward Current (IPC) and the WIBP prove to be a coupled system. Good agreement with the spatial variability shown by satellite imagery. Good response to upwelling events. Isohaline coordinates are a good (although complex) tool to avoid the spatial variability of the plume, helping to understand the involved processes. The plume is characterised: A large-scale river plume, semi-geostrophically balanced (K>>1) and surface-advected (Yankovsky and Chapman, 1987). When compared with other buoyant plume systems, WIBP shares many physical characteristics with the SAB system.

25. Pablo Otero 1, Manuel Ruiz-Villarreal 1, Alvaro Peliz 2 and Jesús Dubter 2 1 Instituto Español de Oceanografía Muelle de las Ánimas s/n, 15002, A Coruña (Spain) 2 Departamento de Física, Universidade de Aveiro, 3810-194, Aveiro, (Portugal) pablo.otero@co.ieo.es

26. DownwellingUpwelling Wind stress Near field Far field Salinity classes Time Area increases in time by increasing of river discharge Northerly winds -> area increases at high salinity classes Expansion

27. Cooling of the WIBP (1) Section 42N

28. Oil spill from Nov 19 06:00h Currents + Wind stress (3%)

29. Coastal circulation before stranding of 2nd spill

30. River plumes NorthWest Iberia is an important fishery and aquaculture area. Strong variability in HABs and fish larvae are been reported. An answer beyond biological behaviour is required. River plumes can play a role in enrichment, concentration and/or retention of biological material (factors pointed by Bakun, 1996) Dispersion is enhanced in the frontal area.