Interannual variability in the Mediterranean Sea

1. Interannual variability in the Mediterranean Sea OBSERVATIONS and MODELLING of the variability in the Mediterranean at basin, sub-basin and local scale Joaquín Tintoré, Vicente Fernández and co-workers IMEDEA (CSIC-UIB) CLIVAR seminar Madrid, 14-15 Febrero

2. Interannual variability in the Mediterranean Index • IMEDEA modeling capabilities at different scales • IMEDEA observational capabilities at different scales • IMEDEA scientific examples of contributions on the ocean variability at different scales • Interannual variability of the Mediterranean circulation

3. IMEDEA modeling capabilities at different scales • Threecirculation modelsare now implemented at IMEDEA: at basin, sub-basin and local scale • DieCAST - DIEtrich Center for Air Sea Technology(Dietrich, 1997). DieCAST is a 3D, PE, control-volume-based, z-level and fourth order accuracy model. The main characteristic of this model is the robustness with a low general dissipation. • HOPS - Harvard Ocean Prediction System(Robinson, 1996, 1999). HOPS is a flexible, portable and generic system for ocean nowcasting and forecastin. The heart of HOPS is a primitive equation dynamical model, which can be coupled to biological models. Data assimilation. • WangCoastal Ocean 3D PE Model: long term collaboration with IMEDEA in coastal ocean modelling since 1989. • Work is also in progress on wave modeling, wave induced coastal currents, interaction with wind induced currents and sediment re-suspension and transport (since 2003).

4. IMEDEA observational capabilities at different scales • Oceanographic cruises at sub-basin scale using different types of research vessels. • Deployment and maintenance ofcurrentmeter mooringsin deep ocean. • XBT’slines using Ships of Opportunity • Argos tracked driftersrelease and monitoring at basin and sub-basin scale andGSM tracked driftersat local and beach scale • Gliders and AUV’s(MERSEA EU funded project)

5. Research examples at IMEDEA From basin to beach scale: Large scale (> 5 km), since 1995 (*): large scale circulation, air-sea interaction, transport in detailed sections, etc. Sub-Basin regional scale (51 km), since 1992: mesoscale/mean flow interactions, blocking basin scale circulation in specific sub-basins, circulation Alboran and Balearic Seas, etc. Local (1 km500m), since 1993: sub-basin-local interaction through canyons, shelf/slope exchanges, circulation in bays, residence times, etc. Towards… beach (50010m), since 2004: fine sediment resuspension by waves and recirculation and sediment transport by wind induced coastal currents in bays and beaches, (only still with PE non hydrostatic models and towards integration with wave models). (*) indicates year of the first paper published in the subject in peer reviewed journals

6. Evaporation Energy (heating) Precipitatio Energy (cooling) Total Flux F/2 Total flux F/2 Q/2 r1(S1,T1) r2(S2,T2) Q/2 Equator Pole Research examples at IMEDEA Large scale variability – thermohaline circulation Box model’s study (Stommel) This transitions can be due to Estochastic resonance: Periodic perturbation plus ambient noise (Velez, Alvarez, Colet, Tintoré, Geophys. Res. Lett., 2001)

7. Research examples at IMEDEA The Palamós Canyon Local scale variability - Canyons • Study of canyon induced shelf/slope exchange. Canyons play an important role enhancing the coastal-open ocean transport Main result: characteristic time scale for shelf-slope exchange 2 months (Jordi et al, Prog. In Oceanog., 2004)

8. Interannual variability in the Mediterranean Observations • WIW (T < 13 C) are present • Blocking of the Ibiza channel No presence of WIW and no blocking

9. MW (WIW) AW Interannual variability in the Mediterranean Mediterranean Sea complexity • Evidences of variability at different scales • Coupling between sub-basin and basin scale circulation through mesoscale interactions. • Coupling between mesoscale, sub-basin and basin scale circulation. Nonlinear effects and interannual variability.

10. Interannual variability in the Mediterranean Sources of ocean variability • Atmospheric (external) forcing: • Seasonal cycle; synoptic episodes; changes in wind stress… • Internal forcing (independent of the atmopheric state): • Non-linear chaotic nature of the ocean: free evolution of instabilities and mesoscale eddies at the scales of the internalRossby radius of deformation: • Ro=NH/f ~ 10 -100 Km in the ocean We have to use numerical ocean models

11. Interannual variability in the Mediterranean Main objectives • Simulation and understanding of the observed variability of the Mediterranean Sea circulation at different time scales (seasonal, intraseasonal and interannual) • Study how many (observed) variability in the real ocean can be due to internal (non-forced) dynamics? Method:model simulations driven by a seasonal atmospheric forcing

12. Interannual variability in the Mediterranean .30 years simulation - no surface temperature or salinity drift – correct parameterization of air-sea thermohaline fluxes Fernández, V., D. E. Dietrich, R. L. Haney y J. Tintoré. Progress in Oceanography. 2004

13. Interannual variability of the Mediterranean The same day two consecutive years Complex circulation with mesoscale structures. Seasonal, perpetual year forcing + interannual response! Fernandez, Dietrich, Haney, Tintoré, Prog. Oceanogr., 2003

14. Interannual variability in the Mediterranean Volume transports Observations: Nortward intrusion of 0.2 to 0.7 Sv in the summer Southward transport of 1 to 1.5 in winter (Pinot et al., 2002) Northward Seasonal and interannual variability Southward Fernandez, Dietrich, Haney, Tintoré, Prog. Oceanogr., 2003

15. Interannual variability in the Mediterranean Volume transports Southward Observations ~ 1-1.5 Sv (geostrophic transport) ( Font et al. 1995) February Fernandez, Dietrich, Haney, Tintoré, Prog. Oceanogr., 2003

16. Interannual variability in the Mediterranean Surface variability Variance of surface pressure at interannual scales (cm2) Algerian sub-basin cm2 The interannual variability occurs at mesoscale

17. Interannual variability in the Mediterranean Conclussions • It has been reproduced, in a a long run simulation, the general circulation of the Mediterranean Sea and its seasonal variability. • It has been found a signal of interannual variability (observed) being non-forced (eddy) associated with the ocean internal dynamics. Study the importance of anomalous heat fluxes (deep water formation in the Gulf of Lions, etc.) in the north-south water transport in the western Mediterranean.  Implication for global thermohaline circulation